A cross-platform tool for recording and plotting digital multimeter data, supporting many popular multimeters from UNI-T, OWON, ANENG, ZOTEK, BSIDE, FNIRSI USB testers, INA226/228 current and voltage monitors, as well as MCP3421 and ADS1115 ADC boards.
This repository provides simple alternative to vendor data collection programs. It works uniformly on Windows, Linux and MacOS. One can use it either from command line or GUI. Since the code is written in python it may be easily incorporated onto your complex measuring or automation system.
The project was started as robust and simple tool for reading data from UNI-T UT61E+ multimeters. Since then the number of other multimeter and USB tester models were supported and the project was extended with the following goals in mind:
- keep code as small and simple as possible
- support for USB and Bluetooth communication channels
- support for dual channel reading and plotting (DC+AC mode of UT61E+ for ex.)
- seamless working on Windows, Linux and MacOS
- convenient working with several devices simultaneously
- single CLI tool (ut61xp-get) for data collection and visualization
- simple GUI frontend application (ut61xp-start) with the same capabilities as CLI tool
- ease of adding new multimeter models
- ease of reuse in other projects
- The UNI-T UT61E+ is high precision low cost digital multimeter with optically isolated USB interface. Despite its popularity it has some disadvantages in current measurement modes, see Examples of DMM models that are not quite suitable for measuring current. The tool works via USB HID adapter D-09A commonly supplied with UT61X+ multimeter. Alternatively one can use UT-D07B Bluetooth adapter which provides the wireless communication channel. However its relatively expensive and very slow. The minimum achievable data readout interval is around 180 msec for USB adapter and around 800 msec for Bluetooth adapter. The latter works especially bad in dual AC+DC mode when timely reading is important.
- The UT61B/D+ models are lower cost 6000 count versions sharing the same DC voltage measuring accuracy of 10µV and having some additional features like thermocouple measuring (UT61D+). They also have smaller shunt resistance for current measurement (100 Ohm vs 500 Ohm for the UT61E+ in µA mode, 1 Ohm vs 5 Ohm in mA mode) at the expense of the worse resolution (0.1 µA vs 0.01 µA, 0.01 mA vs 0.001 mA).
- The UT60BT is inexpensive consumer grade 10000 counts multimeter with built-in BT adapter using the same protocol as UT61X+ devices. It has even better resolution than UT61X+ of 1pF in capacitance mode and 1µV in millivolt mode. Unfortunately, this latter advantage is offset by an annoying hack. To hide fluctuations in readings, the device uses a dead band from -10 µV to +10 µV, where the voltage is always read as zero. Similar dead band exists in A mode between -5mA and +5mA in both UT60BT and UT61E+ while UT61D+ does not have it. Besides it has only two ranges for current measurement. In µA range it has quite high resistance of 3.3 kOhm due to using PTC resettable fuse. Interestingly, the actual shunt resistance is 45 Ohm. So almost all its input resistance comes from the fuse.
The tool supports the number of Bluetooth multimeters using the same 'BDM' protocol. In particular its tested with the following devices:
- The B41T+ is a multimeter with 22000 counts and built-in Bluetooth. However, it is relatively expensive and has a number of disadvantages, including poor display quality and high power consumption when Bluetooth is enabled.
- The OW18E is the most recent 20000 counts model with 1µV resolution. Its better than B41T+ in every respect. It has better display, very low power consumption (1.5mA with BT turned on) and has nice protective rubber sleeve. But at the same time it has one very unpleasant 'feature' - dead band from -5µV to +5µV where input voltage always reads as zero.
- The OW18B is a cheap, low resolution model in OW18 family with built in Bluetooth. It also has better display and lower power consumption than B41T+.
- The CM2100B clamp meter is inexpensive and quite versatile device with 20000 counts capable of measuring AC or DC current without any electrical contact. Note though that while measuring by the clamp it delivers 2000 counts only.
Other compatible OWON multimeters like B35T+ should work with this tool as well.
OWON produces a line of desktop multimeters that use the SCPI communication protocol via USB connection. The tool is tested with XDM1241 model. This is a 55000 count multimeter with 1µV resolution. Its fast on paper but may be painfully slow in practice especially in capacitance mode. It has built in accumulators but does not bother switching itself off draining batteries with 1.2mA current in off state. Other similar models like XDM1041 should work with this tool as well.
OWON produces a line of programmable laboratory power supplies that use the SCPI communication protocol via USB connection. The tool provides the way to read output current value and optionally output voltage in alternative measuring channel. The tool is tested with SPE3051 device. It should be noted that the accuracy of the current values reported by such a device is quite low. It has dead band below 10mA where the current is always reported as zero. Higher current values are reported inaccurately with constant offset of +5mA.
OWON produces a line of programmable electronic loads that use the SCPI communication protocol via USB or RS232 connection. The OEL1515 for example can sink current of up to 15A at the voltage of up to 150V. They provide much better resolution in measuring current and voltage than programmable power sources. These device are not directly supported by ut61xp-get and ut61xp-start tools, but you can interact with them using your own code. See Working with OWON programmable electronic load.
This tool supports Aneng AN9002 model also sold as ZOTEK/BSIDE ZT-300AB. It has 6000 counts display with 10µV voltage measuring resolution, 0.1µA current measuring resolution with 100 Ohm shunt resistance and 1pF capacity resolution. The stand is terrible, the quality of the probes is questionable, but other than that its quite usable with good display and small power consumption (3.5mA with Bluetooth active). Despite such low power consumption it has the best Bluetooth communication range among all tested multimeters. The only thing noticed that may be considered as a drawback is relatively low input impedance in voltage measuring mode. Its around 1 MOhm while other DMM typically have an input impedance of around 10 MOhm.
The Zotek/Aneng multimeters use display segment based encoding for BT communications. So there are as many protocol variants as there are displays in use. Therefore, this tool will not work with other 'Bluetooth DMM' devices like ZT-5B, ZT-5BQ, ZT-5566. Yet the AN9002 is the most interesting model considering the ergonomics and price / performance. The price of this device is smaller than the cost of the single UNI-T Bluetooth adapter.
FNIRSI produces a line of USB testers capable of measuring USB bus voltage, load current and some other parameters. The tool supports reading USB bus current and optionally voltage in alternative measuring channel. Currently supported devices are FNAC28, FNB48P, FNB58 and FNB-C2. The data can be read either via USB or Bluetooth connection (if supported by device). While Bluetooth is convenient the USB connection provides significantly better resolution and reliability.
The INA226 and INA228 are high precision digital current and voltage monitor integrated circuits manufactured by Texas Instruments. They are sold by many vendors in a convenient form, soldered to small printed circuit boards with all necessary connectors. The tool is able to collect readings from such boards by means of additional USB to HID adapter. There are two such adapter boards supported. The first one is based on FTDI FT260 chip. Another one is based on Silicon Labs CP2112 chip. These are inexpensive boars sold by many manufacturers. You only have to connect INA board with USB HID adapter board by 4 wires (GND, VCC, SDA, SCL). After that you will have the precision device for measuring current and voltage at the same time. The INA226 is able to deliver 64k counts while INA228 have 1M counts. Both can be read at the rate of around 10 samples per second. The INA228 module provides current measuring resolution outperforming by an order of magnitude the capabilities of any other multimeter at the fraction of their price. Besides at has precision on-chip temperature sensor. By connecting K-type termocouple instead of the current shunt one can utilize INA228 for temperature measuring in the range from -200°C to 1372°C with high resolution. See Working with INA226/228 current & voltage monitors for more details.
This is inexpensive Analog to Digital Converter chip manufactured by Microchip. They are sold by many vendors in a convenient form, soldered to small printed circuit boards with all necessary connectors. The tool is able to collect readings from such boards by means of additional USB to HID adapter. There are two such adapter boards supported. The first one is based on FTDI FT260 chip. Another one is based on Silicon Labs CP2112 chip. These are inexpensive boars sold by many manufacturers. You only have to connect MCP3421 board with USB HID adapter board by 4 wires (GND, VCC, SDA, SCL). The MCP3421 is able to measure voltage in the range -2.048V .. +2.048V with resolution down to ~2µV.
This is inexpensive Analog to Digital Converter chip manufactured by Texas Instruments. They are sold by many vendors in a convenient form, soldered to small printed circuit boards with all necessary connectors. The tool is able to collect readings from such boards by means of additional USB to HID adapter. There are two such adapter boards supported. The first one is based on FTDI FT260 chip. Another one is based on Silicon Labs CP2112 chip. These are inexpensive boars sold by many manufacturers. You only have to connect ADS1115 board with USB HID adapter board by 4 wires (GND, VCC, SDA, SCL). The ADS1115 is able to measure voltages with resolution down to ~8µV. It has convenient multiplexer fabric able to choose from its four inputs. It may be handy while sampling sequentially several voltage sources by switching them from your python script.
The installation basically involves three steps - getting the source, installing python and installing required packages. Windows users have convenient alternative of using portable binaries.
git clone https://github.com/olegv142/ut61xpy.git
Alternatively you can download source code archive and unpack it.
The easiest way for Windows users is to install Miniconda distribution. Linux typically has python preinstalled. Otherwise, you can install it using the package manager included with your Linux distribution.
On MacOS you typically use Homebrew package manager to install various command line tools. To install it (if not yet installed):
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
echo 'eval "$(/opt/homebrew/bin/brew shellenv zsh)"' >> ~/.zprofile
eval "$(/opt/homebrew/bin/brew shellenv zsh)"
To install python on MacOS:
brew install python python-tk
echo 'export PATH="/usr/local/opt/python/libexec/bin:$PATH"' >> ~/.zshrc
source ~/.zshrc
After these steps you can check the python3 is installed:
python3 --version
The code depends on the following packages:
- hidapi for accessing USB HID devices
- pyserial for accessing USB serial devices
- bleak for accessing Bluetooth devices
- matplotlib for data chart plotting
On Linux you probably can install them with the package manager like
sudo apt install python3-hidapi python3-serial python3-bleak python3-matplotlib
On some systems the package python3-hid is available instead of python3-hidapi.
With Windows Anaconda distribution you should use pip to install packages
pip install hidapi pyserial bleak matplotlib
On MacOS you should create virtual environment first:
cd ut61xpy
python3 -m venv .venv
source .venv/bin/activate
This will create virtual environment in the .venv folder under ut61xpy directory. You will need to activate it by executing source .venv/bin/activate before using the tool. Same steps are applicable on Linux in case you don't want or not able to install packages by package manager.
Now you can install packages in the virtual environment by executing
pip3 install hidapi pyserial bleak matplotlib
To check the tool is now working you can execute Acquisition launcher
./ut61xp-start
The launcher window should appear. If you have compatible multimeter on, you can now try to start collecting data from it. On Windows you have to execute python ut61xp-start since this system does not support the concept of executable python scripts.
Working with sources is the preferred way of using this tool on Linux. On Windows one can just download latest release of portable binaries as self-extracting archive, unpack them to readable folder, then go to the dmm-tools folder and double click ut61xp-start acquisition launcher to start working immediately without any additional installation efforts. See Working with GUI section for more details. To make your work on Windows more convenient you can go to the dmm-tools/scripts folder and double click on the create_links.bat and associate_data.bat scripts. See Working with standalone executables for more details. See also notes about security concerns related to this installation method.
The CLI workflow is built around ut61xp-get script which implements several commands for data acquisition, plotting and simple statistic analysis like making histogram and calculating momentums. The script has many command line options that we discuss briefly in the following sections. We first consider working with UNI-T UT61B/D/E+ multimeters via the standard USB HID adapter UT-D09A typically supplied with the device. After that we will consider working via Bluetooth and communicating with other supported multimeter models.
The ut61xp-get will auto detect UT-D09A USB adapter provided that there is exactly one such adapter connected to your computer. The ut61xp-get list command prints paths for all connected adapters. The ut61xp-get once reads single value from the connected device and prints it to standard output. The ut61xp-get data reads values continuously from the connected device and either prints them or saves to the file if -f/--file option is provided. With -p/--progress option the tool will output dots to standard output while saving values to the file to indicate progress. In case the current reading is invalid (overflowed) the dot will be replaced by exclamation mark. To terminate data reading one can press Ctrl-C. The output file will contain time in seconds since readout start as the first column. With -e/--epoch option the epoch time will be used instead. One can use -d/--delimiter option to set additional delimiter to be used between columns which is the single space by default. With -o/--offset, -m/--mult options the data will be linearly scaled before saving / plotting. These options are handy to remove fixed offset from the data or to convert voltage across current sensing resistor to actual current value. The -i/--interval option may be used to specify data reading interval in seconds. The default interval is zero so that the data is read with maximal possible rate.
In case the file with the name provided with -f option already exists it will be silently overwritten. Therefore, you will either have to use a different name the next time you run data collection, or move the data file to a different location if you need it later. The ut61xp-get tool offers a convenient alternative: automatic file naming. In case the name given with -f option contains % character(s) it will be treated as the template for current date/time formatting as performed by strftime function. Another useful feature is the possibility to add directory part to filename argument. The directory will be automatically created if not yet exists. For example with -f %Y-%m-%d/%H%M%S.data option the file with name representing current time will be placed to the directory with the name representing current date. In case the name given with -f option contains ${MODEL} substring, it will be replaced by the currently used multimeter model making filenames more informative.
Dual channel mode is handy while reading data in DC+AC mode of UT61E+. To use this feature you will need to choose proper mode on the multimeter mode dial and specify filename for storing second channel by means of -a/--alt-file option. Other multimeter models may support dual channel reading for AC voltage and frequency in particular. Programmable power sources and USB testers may report the load current and voltage.
The ut61xp-get data command will plot data read from device in separate window if -g/--graph option is provided. To terminate data reading in such mode one can just close graph window. With dual channel mode the graph window will contain two plots. The -w/--wnd option may be used to limit the number of recent data samples utilized to produce the plot by the specific number. Alternatively, if expressed as negative number of seconds the -w/--wnd option will limit the time range of the plot. You can switch window mode on / off while plotting data by pressing 'w' hot key in the plot window. One can add any number of additional horizontal lines at specific levels to mark some specific value boundaries with --hline and --alt-hline options (the latter draws them on the second channel plot). These options may be used multiple times to add multiple horizontal lines. There are several other options that can be used for styling the graph window. One can set window title (-t/--title), plot title (--plot-title, --alt-title), data line style (--line-style), horizontal line style (--hline-style), data line colors (--line-color, --alt-line-color), horizontal line color (--hline-color). In case plot title is not provided as command line argument the current measuring mode reported by multimeter will be used as the title. In case window title is not provided as command line argument the multimeter model will be used as the title. You can use plot navigation bar as usual. In particular, you can use pan/zoom controls of the graph window while reading the data or use the dedicated button to save plot to the file, yet the acquisition will be paused until you done with plot saving. Additionally double clicking the plot will toggle full screen mode. To open the graph window in full screen mode from the start, you can use the --full-screen command line option. With '-z/--with-zero' the zero value will always be included in the displayed vertical axis range. This will help to understand the scale of the signal fluctuations with respect to the signal value. Pressing 'z' key in plot window switches 'with-zero' mode on / off regardless of the '-z/--with-zero' option.
The ut61xp-get plot command followed by the list of filenames plots the data sets reading them from the given files. It is just a convenient tool for viewing the collected data without any complex charting features. You can use plot navigation bar as usual and use double click to toggle full screen mode. While plotting single file you can press space to print statistics to console or press t to toggle showing statistics on the plot window. See Printing data statistics section for more details.
The data reported by multimeter typically contains information about measurement mode (say voltage) and/or measurement units (say millivolts). The units may be voluntary changed by the device as a result of the automatic range selection (for ex. millivolts to volts). Many vendor provided and third party data readout applications just save data in the units reported by device. This practice is bad since the data with sudden change of units will show abrupt jump with several orders of magnitude and will look as a mess overall. The ut61xp-get tool takes special care to guarantee that the units of the data will be the same no matter how auto-ranging works on the particular device. The particular units used for the data representation will be shown as the default plot title with -g option and will be saved in the first line of the output file with -f or -a options.
The configuration is the file storing the full set of command line options in the form of json dictionary. Use --cfg-save option with ut61xp-get data command to create such file filled with options specified in the current command line and -c/--cfg-load option to load such file back. They may be handy to save typing and even more importantly to make data acquisition from several devices easier. Several examples of using them while working with several devices simultaneously will be given below.
With -s/--stat option the ut61xp-get data command will print various collected data statistic metrics upon acquisition termination. In particular:
- the number of data samples (total and valid)
- the min / max values
- the median and pure average values
- the standard deviation (absolute and relative)
- the integral in val * sec units
- the 3rd central moment relative to the standard deviation (skewness)
- the 4th central moment relative to the standard deviation minus 3 (kurtosis exess)
The last two metrics may be used to characterize deviations from the mean. The smaller they are the closer the value distribution to the standard one with Gaussian noise.
With -S/--plot-stat option the ut61xp-get data command will show data statistics on the plot window and update it on every new data sample. The --plot-stat-loc option may be used to specify the particular location on the plot where the statistics box will be placed. The default is 'lower left'. With --plot-stat-loc "best" options the location will be chosen automatically to minimize overlapping with data curve. The statistic display area may be shown / hidden while plotting by pressing 't' key. This hot key works regardless of the -S/--plot-stat option. Another way to view current statistics is to press the space bar in the chart window. This will print the statistics on the terminal so you can easily copy / paste them.
The ut61xp-get stat input_file command prints statistics of the data stored in the given input_file.
The following keys (partially discussed above) have special meaning when pressed in the data plot window:
| key | meaning |
|---|---|
| space | print current statistics to terminal so you can easily copy/paste them |
| t | show / hide statistics display area on the plot |
| w | turn data window on / off (provided that it was initially configured by -w/--wnd option) |
| z | turn on / off 'with-zero' mode |
| p | toggle pan / zoom mode |
| o | toggle zoom to rectangle mode |
| left / right arrow | iterate over list of recent views |
| c, Backspace | switch to the previous view |
| r, h, Home | reset view |
| s, Ctrl+s | opens file chooser dialog to save plot chart as an image |
| double click, f, Ctrl+f | toggle full screen mode |
| q, Ctrl+w | close plot window |
Some of these hot keys are implemented by matplotlib library. Note that in panning / zooming mode the window will stop updating itself on every new data sample. Yet the data acquisition will run as usual. Saving figure as an image will pause data acquisition till saving completion, so use this feature with caution. Switching view does not terminate panning / zooming mode which may be confusing sometimes.
The ut61xp-get hist input_file command creates histogram for the given input file. It either prints it to standard output or saves to the file if -f/--out-file option is given. The output data formatting may be customized by -d/--delimiter option. The -b/--bins option may be used to set the required number of bins in the histogram. With -g/--graph the histogram will be plotted in the separate window. One can plot the histogram saved to the file by ut61xp-get plot command as any other data file.
Execute ut61xp-get tool with -h option to get detailed information about command line options. On Windows:
python ut61xpy/ut61xp-get -h
python ut61xpy/ut61xp-get data -h
python ut61xpy/ut61xp-get hist -h
On Linux the following will work either:
./ut61xpy/ut61xp-get -h
./ut61xpy/ut61xp-get data -h
./ut61xpy/ut61xp-get hist -h
Suppose we have UT61E+ and UT61D+ devices and are going to read data from them simultaneously. We use different models just for illustrative purpose, they may be the same. We can find out path to each device by connecting them one by one and using ut61xp-get list command. After that we can pass the path to ut61xp-get data command like ut61xp-get --path PATH data OPTIONS but it takes a lot of typing. Using configurations may make life easier. One can do the following
- Connect first device (UT61E+) only and issue the command:
python ut61xpy/ut61xp-get data -gps -f e.data -t UT61E+ --cfg-save ut61e.cfg
It will auto detect device, plot the data saving it to the file e.data, showing a progress and printing stats on termination. It will also create the configuration file ut61e.cfg. The -t option will set window title so we can tell which window shows data from which device.
- Disconnect first device and connect other device (UT61D+) and run the command:
python ut61xpy/ut61xp-get data -gps -f d.data -t UT61D+ --cfg-save ut61d.cfg
The corresponding configuration will be saved to ut61d.cfg
- Now we can connect both devices and run some acquisition in parallel (in separate terminals):
python ut61xpy/ut61xp-get data -c ut61d.cfg
python ut61xpy/ut61xp-get data -c ut61e.cfg -a a.data
The first command will read data from UT61D+. The second command will acquire data from UT61E+ in DC+AC mode storing AC channel samples to a.data.
- One can even create specialized configuration file for DC+AC mode by modifying basic configuration:
python ut61xpy/ut61xp-get data -c ut61e.cfg -a a.data --cfg-save acdc.cfg
Now one can just execute the following short command line to use DC+AC readout with dual plot graph:
python ut61xpy/ut61xp-get data -c acdc.cfg
Of cause the ./ut61xpy/ut61xp-get invocation will work on Linux as well since ut61xp-get is executable script on this system. Note that to be able to combine measurements made by different devices you will probably have to use epoch time option (-e). Otherwise data samples originated from different devices may be read at different time even if they have the same time stamp (since its relative to acquisition start of the particular readout session).
The configuration tricks shown above work just because the auto-detected device path becomes part of the configuration saved with --cfg-save option. One can check that by looking at the configuration file content saved as text. But what is the device path after all? It turns out that on Windows it contains some unique device identifier but on Linux it depends only on the USB port where the device is attached. So its critically important to use different ports for different devices and always use the same port for the particular device while working with configurations / device paths on Linux.
Working with Bluetooth adapter conceptually is not different from using USB. Just add -B/--bt option right after ut61xp-get to force script to use BT adapter. Similar to USB use case the script is able to auto detect BT adapter provided that its powered on and no other adapters are in the accessible range. By means of using the --cfg-save option one can save the address of the adapter discovered (which plays the role of USB device path) for the subsequent reuse. One can specify BT address in the command line explicitly via --path/--addr option. Opening BT device by its address is significantly faster and more reliable than autodetecting it.
Some devices need special settings not applicable to other device. There is a special command line option to setup such parameters --param. It should be followed by KEY=VAL pair. To set multiple parameters this option may be used multiple times like --param KEY1=VAL1 --param KEY2=VAL2 ... To setup parameters in ut61xp-start data acquisition launcher GUI one should use device parameters field separating key=value pairs by comma. The following table lists all possible parameters and notes where they are applicable. Note that the parameter names are case-insensitive.
| Parameter name | Meaning | Default | Applicable to |
|---|---|---|---|
| tout | Data read timeout in seconds | device specific | any device |
| vid, pid | The USB VID, PID numbers in case you need to change default ones | device specific | USB device |
| btname | Bluetooth device name in case you need to change default one | device specific | BT device |
| baud | The USB CDC device serial baud rate | 115200 | USB CDC device |
| i2c | I2C to USB adapter for INA device {FT260,CP2112} | FT260 | I2C device |
| addr | I2C address | device specific | I2C device |
| shunt | Shunt resistance for INA current & voltage monitors | 0.1 Ohm | INA226/228 |
| range | INA228 shunt voltage range {0,1} | 0 | INA228 |
| tempco | INA228 shunt temperature coefficient | 0 | INA228 |
| amode | INA228 alternative readout mode {cv,vt,tc,ktv,ktt} | cv | INA228 |
| gain | ADC amplifier gain | device specific | MCP3421, ADS1115 |
| mux | ADC input multiplexer configuration | 0 | ADS1115 |
| again | Alternative channel ADC amplifier gain | 0 | ADS1115 |
| amux | Alternative channel ADC input multiplexer configuration | 7 | ADS1115 |
By default, the ut61xp-get tool expects the UT61X+ multimeter as the target device. To change this, one should use -M/--model option. In case device works via Bluetooth, the -B option must be provided with -M/--model option. Both options should be specified right after ut61xp-get in the command line. The required options for the particular model family are listed in the following table. The last column of the table shows corresponding model label used in ut61xp-start GUI frontend application, see Working with GUI.
| Vendor | Model family | Command line options | Model label in ut61xp-start UI |
|---|---|---|---|
| UNI-T | UT61B/D/E+ | -M UT61X+ | UT61X+ USB |
| UT61B/D/E+ with UT-D07B Bluetooth adapter | -M UT61X+ -B | UT61X+ BT | |
| UT60BT | -M UT60BT -B | UT60BT BT | |
| OWON | Bluetooth multimeters | -M OWON -B | OWON BT |
| Desktop multimeters with USB port | -M SCPI-DMM | SCPI-DMM USB | |
| Programmable power supply with USB port | -M SCPI-CV | SCPI-CV USB | |
| ANENG | AN9002 Bluetooth multimeter | -M ANENG -B | ANENG BT |
| ZOTEK/BSIDE | ZT-300AB Bluetooth multimeter | -M ANENG -B | ANENG BT |
| FNIRSI | FNAC28 USB tester | -M FNAC28 | FNAC28 USB |
| FNB48P USB tester via USB connection | -M FNB48P | FNB48P USB | |
| FNB48P USB tester via Bluetooth | -M FNB48P -B | FNB48P BT | |
| FNB58 USB tester via USB connection | -M FNB58 | FNB58 USB | |
| FNB58 USB tester via Bluetooth | -M FNB58 -B | FNB58 BT | |
| FNB-C2 USB tester | -M FNB-C2 | FNB-C2 USB | |
| TI | INA226 with I2C to USB adapter | -M INA226 | INA226 USB |
| INA228 with I2C to USB adapter | -M INA228 | INA228 USB | |
| ADS1115 with I2C to USB adapter | -M ADS1115 | ADS1115 USB | |
| Microchip | MCP3421 with I2C to USB adapter | -M MCP3421 | MCP3421 USB |
The INA226/228 chips are typically sold with shunt already soldered to the board. Yet there are some number of steps required before you can read data from them:
- Choose I2C to USB adapter board. Currently supported boards are FT260 and CP2112.
- Connect INA board to I2C USB adapter board by 4 wires. The GND and VCC signals provide power, SDA and SCL are for I2C bus to read the data.
- Provide I2C adapter name to the tool as command line option like --param i2c=CP2112 or by adding i2c=CP2112 to the comma-separated list of key=val pairs in the device parameters field of ut61xp-start application window. This is not necessary if you are using the default FT260 adapter.
- Setup shunt resistance either by command line option like --param shunt=.015 or by adding corresponding key=val pair to the device parameters field of ut61xp-start application window. This is not necessary if you have a default 0.1 Ohm shunt or does not want to measure current.
At this point you should be able to read current from the INA226/228 board and optionally read voltage from it as alternative measuring channel if you provide -a/--alt-file option or check alternative channel output field in ut61xp-start application window.
Several important things should be noted:
- The INA module ground (GND) must not be left floating. You should connect it either to the ground of the circuit you are monitoring or to the IN- current measuring terminal. Otherwise you can damage the INA module.
- The USB adapter does not isolate your computer from the circuit being monitored. So if your computer and monitored circuit are not perfectly isolated or the monitored circuit is at dangerous electric potential you must add USB isolation between your computer and I2C to USB adapter. Another option is to add isolation at the I2C bus between USB adapter and INA chip. To achieve such isolation, one can use, for example, the ISO1540 chip, which is also available as ready-to-use modules.
The INA228 adds several options to the measuring setup since it has the third channel for chip temperature measuring. The tool can collect data from two measuring channels only. Scripts can read temperature measuring channel directly (see code examples). But for saving / plotting any pair of these three channels one can use amode parameter (see Setting device-specific parameters). The following table shows possible values of this parameter and their meaning.
| Alternative readout mode | Primary channel | Alternative channel |
|---|---|---|
| cv | Current | Voltage |
| vt | Voltage | Chip temperature |
| tc | Chip temperature | Current |
| ktv | K-termocouple temperature | Voltage |
| ktt | K-termocouple temperature | Chip temperature |
The first readout mode is the default one. The last two modes are special since they provide the possibility to measure temperature with K-termocouple connected in place of the shunt resistor. Its termoelectric potential is measured and combined with chip temperature by the tool to produce the termocouple junction temperature reading. The IN- terminal in such setup should be connected to the INA module ground to reduce noise. Setting the shunt resistance (which is absent) is not necessary in such usage scenario. The termocouple temperature readings should be accurate down to 0.05°C in the range from -200°C to 1372°C. The scripts are not required to setup alternative readout mode since they can read any measuring channel directly. See termocouple readout example.
Another possible use of the INA228 temperature sensor is shunt temperature compensation. To utilize it one can set tempco parameter (see Setting device-specific parameters). After that the current readings will be multiplied by compensation factor 1 + (T - 25) * tempco, where T is the chip temperature. This does not give you the perfect compensation though since T is not equal to the temperature of the shunt. Increasing the tempco to compensate the difference will improve the accuracy provided that the environment temperature is stable.
The full scale shunt voltage measuring range of INA228 is ±163.84mV. It may be reduced by the factor of 4 improving measuring resolution by setting range parameter to 1. It can be done in command line by option --param range=1 or by adding range=1 to the comma-separated list of parameters in the device parameters field of ut61xp-start application window.
To read the data from MCP3421 Analog to Digital Converter you need to connect it to I2C adapter board similar to the case of INA226/228 boards described above. The MCP3421 has single channel with 18 bits resolution which gives you 131072 counts with positive and negative signs. The ADC has full scale range from -2.048V yo +2.048V. The built in programmable gain amplifier (PGA) may be set to amplify signal by the factor of 2, 4 or 8 reducing full scale range accordingly. You can set PGA gain by specifying gain parameter either in command line or by option --param gain=N or by adding gain=N to the comma-separated list of parameters in the device parameters field of ut61xp-start application window. With maximum gain 8 the ADC has resolution of about 2µV. Therefore you can use it for measuring termocouple voltage in particular. The default value of the gain is 1 so that MCP3421 will use its full scale range of 2.048V.
The MCP3421 has differential input that gives you the possibility to measure negative signals while keeping input voltages within the power rails. Note that similar to INA226/228 case you should avoid inputs floating. They should always have predictable potential with respect to the ground. These potentials should always be kept within the power rails of the board. For example, while measuring termocouple voltage you can connect negative input to the board's ground. The USB isolation may be necessary to decouple system being measured from the computer reading the data.
To read the data from ADS1115 Analog to Digital Converter you need to connect it to I2C adapter board similar to the case of INA226/228 and MCP3421 boards described above. The ADS1115 has 16 bits resolution which gives you 32768 counts with positive and negative signs. Despite lower resolution than MCP3421 it has its own benefits that could make it the preferred choice:
- wider full scale range up to 6.144V
- input multiplexer that allows you to sample up to 4 input signals
- configurable I2C bus address so you can attach up to 4 such devices to the same I2C adapter
The input multiplexer configuration can be set by mux parameter either in command line or by option --param mux=M or by adding mux=M to the comma-separated list of parameters in the device parameters field of ut61xp-start application window. By default device is using its AIN0 as positive terminal and AIN1 as negative input voltage terminal. The following table illustrates possible values of the mux parameter and their meaning
| mux parameter | positive terminal | negative terminal |
|---|---|---|
| 0 | AIN0 | AIN1 |
| 1 | AIN0 | AIN3 |
| 2 | AIN1 | AIN3 |
| 3 | AIN2 | AIN3 |
| 4 | AIN0 | GND |
| 5 | AIN1 | GND |
| 6 | AIN2 | GND |
| 7 | AIN3 | GND |
The gain parameter can be used to specify ADC preamplifier gain which affects full scale range and resolution as shown in the following table
| gain parameter | full scale range (V) | resolution (µV) |
|---|---|---|
| 0 | 6.144 | 187.5 |
| 1 | 4.096 | 125 |
| 2 | 2.048 | 62.5 |
| 4 | 1.024 | 31.25 |
| 8 | 0.512 | 15.625 |
| 16 | 0.256 | 7.8125 |
The default value of the gain is 0 so that ADS1115 will use its full scale range of 6.144V.
In case you are going to read alternative data channel you may configure its multiplexing and gain by specifying amux and again parameters. So you will be able to sample and plot two voltage sources connected to different ADS1115 inputs. The default value of again is 0 (full scale range of 6.144V). The default amux is 7 so you will sample AIN3 input relative to the ground.
The GUI workflow is built around ut61xp-start script that provides convenient UI for setting ut61xp-get options and launching data acquisition in separate processes. The single instance of ut61xp-start UI can launch any number of data acquisition processes working in parallel, saving data to separate files and showing collected data in their own data plot windows. The following figure illustrates using data acquisition GUI reading data from 3 multimeters simultaneously on Raspberry Pi5.
The ut61xp-start script opens window with controls providing convenient way of setting data acquisition and plotting options and launching data acquisition in separate windows as if they were opened by running ut61xp-get tool from command line. The launcher window consists of the following major parts:
- the multimeter model selector
- the data acquisition options (for ex. output file name)
- the plot styling options (for ex. the plot title)
- the acquisition start button
Note that there are no options that don't have default values. So one can just choose spectrometer model and press start button. Initially the model list contains only 'unbounded' models. See Working with other supported devices for the complete list of the supported models. Once the tool connects to the particular multimeter by autodetecting it, the 'bounded' model with particular USB path / BT address assigned is added to the list of models. So you can easily connect to the same multimeter later by choosing the particular bounded model. The full set of configured options is saved and restored whenever you select the particular model. Pressing Start button launches data acquisition process in separate window. This window has the same set of useful hot keys as described in Plot window hotkeys section. The data collected is being saved to the file with the path configured in the launcher window. By default the output file is located in 'data' folder next to the ut61xp-start tool in subfolder with current date as the name. Its name is made by concatenation of the start time and multimeter model name. The real path to the last created data file is shown on ut61xp-start tool window right below the file path template. To stop data acquisition one can just close the acquisition window.
The ut61xp-start has command line option --tight that makes it appearance more compact to better fit low resolution screens.
On Windows the standalone/build_sfx.bat script builds standalone executables in standalone/dist/dmm-tools folder. It then creates a self extracting archive standalone/dist/dmm-tools-{VERSION}.exe provided that you have 7-Zip installed. This archive can be extracted to any folder on the target system including the flash drive. The only requirement for the folder where the executable files will be placed is the ability to write to it. Since the application is 'portable' it tends to store all its files next to the executable. The Program Files folder on Windows is usually write-protected, so you should choose a different location to store executable files.
The dmm-tools/scripts folder contains several .bat files that can make setting up your Windows environment easier:
| Script | What it does |
|---|---|
| create_links.bat | creates links to executables and data folder on your Windows desktop |
| delete_links.bat | removes links from your Windows desktop |
| associate_data.bat | associates output files with .data extension with data plotting executable |
| deassociate_data.bat | removes output files association with data plotting executable |
| clear_config.bat | drops saved configurations reverting all settings to default values |
On Linux one can build executables by the following command
pyinstaller dmm-tools.spec --noconfirm
Note that the resulting size of these executables on Linux is drastically larger than on Windows which makes this installation method practically meaningless.
There are several other tools that are actually wrappers around ut61xp-get tool. They make using particular functionality easy especially on Windows as described in the following table.
| Tools | What it does |
|---|---|
| ut61xp-plot | Plots one or more files given as command line arguments similar to ut61xp-get plot command. On Windows one can drag and drop one or more files to this tool to plot them. |
| ut61xp-hist | Plots histogram for the file passed as command line arguments similar to ut61xp-get hist command. On Windows one can drag and drop file to this tool to plot its histogram. |
| ut61xp-stat | Prints statistics for the file passed as command line arguments similar to ut61xp-get stat command. On Windows one can drag and drop file to this tool to print its statistics. |
For convenience you can associate .dat files with ut61xp-plot tool. To do it right click such file, choose 'Open with', then select 'Choose another app', then click 'Choose an app from your PC' at the bottom of the list, then select ut61xp-plot tool in the file chooser and finally click 'Always' button. Now the ut61xp-plot tool will plot .dat file every time you double click it.
The ut61xp-start tool creates several files and directories next to executable to save data, logs and other execution artifacts. By default only data directory is visible. It contains sub-folders named by creation date with data files having time and multimeter model as parts of their names by default. The user may change the name of the output file in ut61xp-start window if necessary. There are several other files and folders with names started with dot. One should use ls with -a switch to see them on Linux or enable 'Show hidden and system files' option in 'System/Advanced/File Explorer' settings on Windows. They are listed in the following table.
| Path relative to executable location | Description |
|---|---|
| data/ | Folder for storing output data (by default) |
| .config | File storing models configuration as json dictionary. One can drop it if something goes wrong. It will be recreated automatically on next ut61xp-start tool invocation. |
| .cfg/ | Folder storing configuration files for recent acquisition runs with names constructed from multimeter model name and communication protocol like 'OWON_BT'. So one can invoke acquisition with the same settings from command line by executing ut61xp-get data -c .cfg/CONFIG_NAME |
| .logs/ | Folder with ut61xp-start tool execution logs. One can examine them should something goes wrong or send to the author for analysis. |
| .internal/ | Folder containing executable components such as a shared libraries and compiled Python code. |
If something goes wrong you may consider looking to the logs and/or add --verbose option to ut61xp-get and ut61xp-start command line.
The multimeter becomes available for reconnect after dropping of the previous connection. The problem here is that its the operating system that maintains connection. It may not drop connection if application that initiated it was terminated not gracefully, especially on Linux. So the multimeter thinks its still connected to already terminated application. The problem occurs if one close ut61xp-start window while some data acquisition windows are still open. In case all such windows are closed before closing ut61xp-start window the Bluetooth connections are terminated as expected.
Closing ut61xp-start window while acquisition is still active terminates acquisition process without saving anything. Therefore, if you need the collected data, please close the acquisition plot window first.
Aneng (ZOTEK/BSIDE) multimeter is powering off automatically after some time while data collection is running
The auto power off feature powers off device after 15 min of inactivity. The Aneng (ZOTEK/BSIDE) multimeters don't consider Bluetooth connection as 'activity'. To disable auto powering off you should press and hold the SEL button while powering on multimeter and selecting desired mode with mode dial. The SEL button should be held until you hear four beeps. The auto power off feature will be disabled until the next power on. With power off disabled the multimeter will still emit alarming beeps periodically but will not power off.
The Windows protected your PC warning always appears on attempt to run self extracting distribution archive
This happens because Windows flags all unsigned executables downloaded from the web as untrusted. There are two ways to overcome it. You can click More info and press Run anyway button. Otherwise you can clean this flag in advance by right clicking the executable and checking Unblock on the General tab of the file Properties.
There are several system services used to be installed by default that may open connected device preventing its discovery by ut61xp-get or ut61xp-start tools. Try to the execute the following commands in the terminal and reconnect your device.
sudo apt remove brltty
sudo systemctl stop ModemManager
sudo systemctl disable ModemManager
To fix it find the adapter in Device Manager / Human Interface Devices (VID = 0x10C4, PID = 0xEA90), open its Power Management properties and uncheck 'Allow the computer to turn off this device to save power'.
Most probably you have left INA module ground floating while measuring current. Connecting only two current terminals of the INA module to electric circuit while measuring current seems logical, similar to using a digital multimeter. However, due to differences in the measuring circuits, this results in very high noise levels during measurement and in some cases may even damage the INA module. Its strongly recommended to attach the INA module ground either to the ground of the circuit being measured or connect it directly to the negative current terminal. Its also strongly recommended to add USB isolation between you computer and I2C USB adapter board.
An attempt to access the device as plain user may fail on Linux due to restrictive permissions. To be able to access the USB serial port you either have to run the ut61xp-get or ut61xp-start tool as a root or add iself to dialout group:
sudo usermod -aG dialout $USER
You have to re-login or reboot to apply new group membership properly. Note that this approach does not work with HID devices (see below).
An attempt to access the HID device as plain user may fail on Linux due to restrictive permissions. To be able to access the USB HID device you either have to run the ut61xp-get or ut61xp-start tool as a root or execute the following:
sudo groupadd -r hidaccess
sudo usermod -aG hidaccess $USER
echo 'SUBSYSTEM=="usb", GROUP="hidaccess", MODE="0664"' | sudo tee /etc/udev/rules.d/99-hid-access.rules
You have to re-login or reboot to apply new group membership properly.
To add new device you should implement its adapter class inherited from Device and BTMixin or USBMixin from device.py (see Base classes below). Then the class type should be added to _supported_devices from ut61xp-get and that's it. In case the device is using already supported protocol but having different USB VIP/PID or Bluetooth device name, one can try to connect to it by tweaking these parameters by --param vid=.., --param pid=.., --param btname=.. command line options.
Just add this project as the sub-module to your source tree and import the necessary device adapter from it.
Every supported device is represented by an instance of its adapter class. There are 2 major families of such adapters - USB and Bluetooth adapters. There is also a specialized case of USB devices that uses SCPI protocol for communication. The following figure provides the simplified view of the class hierarchy.
The Device class (from adapters/device.py) is the ancestor of all multimeter adapters regardless of the communication protocol used. It defines several methods that should be used for communicating with the target device. The init method initializes communication session. The query_raw method reads data from the device and returns them as opaque object. The get_value method extracts floating point value from the data returned by query_raw method. The get_mode method returns measurement mode and/or units description string. The source of this information may vary. Some implementation may query and store it in the init call. Others may extract it from the raw data returned by query_raw method.
The USBMixin and BTMixin classes are used as a second base class for USB and Bluetooth spectrometer adapters respectively. They provide methods for device discovery and adapter instance creation. The list_paths and list_addrs methods return list of USB device paths and Bluetooth device addresses that may be related to corresponding devices. The open_path and open_addr methods create device adapter instance given USB path or Bluetooth address respectively. The open method auto detects the device and creates its adapter instance provided that there is a single such device connected to USB or reachable via Bluetooth.
The SCPIDevice is specialized base class for multimeters and other devices using SCPI protocol for communicating with the host. It implements several methods that can be used to directly call SCPI API of the particular device. The scpi_send method sends SCPI command to the device, the scpi_receive method reads the response from the device. The scpi_call method just does scpi_send and scpi_receive calls and returns the response. The scpi_query method invokes scpi_call and converts the response to the floating point value. We will consider using this methods for accessing SCPI device not supported by ut61xp-get and ut61xp-start tools in the example of working with OWON programmable electronic load.
The code examples below illustrate techniques that can be used while working with various devices.
The following code will read data from OWON Bluetooth multimeter continuously. It will discover the multimeter automatically provided that you have single one nearby.
from ut61xpy.adapters.owon import OwonBtDevice
if dev := OwonBtDevice.open():
with dev:
dev.init()
while dev.is_connected():
if data := dev.query_raw():
print(dev.get_value(data), dev.get_mode(data))
else:
breakIf you know the Bluetooth device mac address, you can open it faster without scanning. It will also work if you have several multimeters. The following code will read Aaneng AN9002 or compatible ZOTEK/BSIDE ZT-300AB with particular address.
from ut61xpy.adapters.aneng import AnengBtDevice
if dev := AnengBtDevice.open_addr('C4:A9:B8:3A:5B:A2'):
with dev:
dev.init()
while dev.is_connected():
if data := dev.query_raw():
print(dev.get_value(data), dev.get_mode(data))
else:
breakWhile working with OWON desktop multimeter, you can not only read measured values, but also configure measuring mode and input range. The following code will set mode to DC voltage with 5V range and then read samples continuously two times per second. Note that reading with maximum possible rate does not make sense in such case. The OWON multimeter does not refresh returned value faster than several times per second even if the sampling rate is much higher on specs.
import time
from ut61xpy.adapters.scpi import SCPIDmm
if dev := SCPIDmm.open():
with dev:
dev.scpi_send(b'CONF:VOLT:DC 5')
dev.init()
while dev.is_connected():
if data := dev.query_raw():
print(dev.get_value(data), dev.get_mode(data))
time.sleep(.5)
else:
breakWhile working with OWON programmable power source, you can not only read voltage and current, but also configure the power source output. The following code will configure OWON power source, turn on its output, wait 2 seconds, print current and voltage and switch output off.
import time
from ut61xpy.adapters.scpi import SCPIPowerSource
if dev := SCPIPowerSource.open():
with dev:
dev.init(2)
dev.scpi_send(b'VOLTage 10')
dev.scpi_send(b'CURRent 1')
dev.scpi_send(b'OUTPut 1')
time.sleep(2)
if data := dev.query_raw():
print(dev.get_mode(data, dev.CURR_CHAN), ':', dev.get_value(data, dev.CURR_CHAN))
print(dev.get_mode(data, dev.VOLT_CHAN), ':', dev.get_value(data, dev.VOLT_CHAN))
dev.scpi_send(b'OUTPut 0')Note that there are also VOLTage:LIMit and CURRent:LIMit parameters. If any of them is exceeded the OWON power source switches off its output showing warning on the screen. The error is cleared by switching output off either by OUTPut command or by button on the front panel. Therefore, if you need just current limiting, then take care to always have VOLTage:LIMit > VOLTage and CURRent:LIMit > CURRent.
Similarly to programmable power source, you can read voltage and current from FNIRSI USB tester with the following code:
from ut61xpy.adapters.fnirsi import FNB58Usb
if dev := FNB58Usb.open():
with dev:
dev.init(2)
while dev.is_connected():
if data := dev.query_raw():
print('%.4f%s\t%.4f%s' % (
dev.get_value(data, dev.VOLT_CHAN), dev.get_mode(data, dev.VOLT_CHAN),
dev.get_value(data, dev.CURR_CHAN), dev.get_mode(data, dev.CURR_CHAN)
))
else:
breakTo communicate with FNB58 via Bluetooth one can just replace FNB58Usb -> FNB58Bt.
The next code example illustrates reading data from Aneng and OWON Bluetooth multimeters simultaneously.
from ut61xpy.adapters.aneng import AnengBtDevice
from ut61xpy.adapters.owon import OwonBtDevice
devs = (AnengBtDevice.open(), OwonBtDevice.open())
if all(devs):
for d in devs:
d.init()
while all(d.is_connected() for d in devs):
data = [d.query_raw() for d in devs]
if all(data):
print('%f %s\t| %f %s' % (
devs[0].get_value(data[0]), devs[0].get_mode(data[0]),
devs[1].get_value(data[1]), devs[1].get_mode(data[1])
))
else:
break
for d in devs:
if d:
d.close()The OWON OEL series electronic loads are not directly supported by ut61xp-get and ut61xp-start tools, but you can interact with them using your own code. The following code will open connection to such device given the port name ('COM42'). Then it will configure it in constant current mode and run test sequence linearly increasing load current and printing measured current and voltage. The code is tested with OEL1515 model.
import time
from ut61xpy.adapters.scpi import SCPIDevice
CMD_DELAY = .1
STEP_DELAY = .5
STEP = .1
STEPS = 20
if dev := SCPIDevice.open_path('COM42'):
with dev:
print('connected to', dev.get_model())
dev.scpi_send(b'SYST:REM')
time.sleep(CMD_DELAY)
dev.scpi_send(b'FUNC CURR')
time.sleep(CMD_DELAY)
dev.scpi_send(b'INP 1')
time.sleep(CMD_DELAY)
curr = 0
print('Set\tCurr\tVolt')
for i in range(STEPS+1):
dev.scpi_send(b'CURR %f' % curr)
time.sleep(STEP_DELAY)
print('%.2f\t%.3f\t%.4f' % (curr, dev.scpi_query(b'MEAS:CURR?'), dev.scpi_query(b'MEAS:VOLT?')))
curr += STEP
dev.scpi_send(b'INP 0')
time.sleep(CMD_DELAY)
dev.scpi_send(b'SYST:LOC')The next code example illustrates interfacing with electronic load in similar setup but with OWON desktop multimeter (XDM1041, XDM1241) measuring current between power source and electronic load. The script prints current set, current reported by electronic load and the current error with respect to the value reported by multimeter. Note that unlike other examples the code uses SCPIDevice class and its scpi_query method for interacting with multimeter instead of generic query_raw/get_value API.
import time
from ut61xpy.adapters.scpi import SCPIDevice
CMD_DELAY = .1
STEP_DELAY = 1.5
STEP = .1
STEPS = 20
dmm = SCPIDevice.open_path('COM11')
el = SCPIDevice.open_path('COM42')
if dmm and el:
dmm.scpi_send(b'CONF:CURR:DC 5')
el.scpi_send(b'SYST:REM')
time.sleep(CMD_DELAY)
el.scpi_send(b'FUNC CURR')
time.sleep(CMD_DELAY)
el.scpi_send(b'INP 1')
time.sleep(CMD_DELAY)
curr = 0
print('Set\tCurr\tErr')
for i in range(STEPS+1):
el.scpi_send(b'CURR %f' % curr)
time.sleep(STEP_DELAY)
curr_el = el.scpi_query(b'MEAS:CURR?')
curr_dmm = dmm.scpi_query(b'MEAS?')
print('%.2f\t%.4f\t%.4f' % (curr, curr_el, curr_el - curr_dmm))
curr += STEP
el.scpi_send(b'INP 0')
time.sleep(CMD_DELAY)
el.scpi_send(b'SYST:LOC')
if dmm:
dmm.close()
if el:
el.close()While working with INA current & voltage monitors from your scripts its necessary to setup several important things:
- set I2C adapter type unless you are using the default FTDI FT260 board
- set shunt resistance unless you have the default 0.1 Ohm shunt
The following code example illustrates reading current and voltage from INA226 module with 15mOhm shunt via CP2112 adapter.
from ut61xpy.adapters.ina import INA226Device, CP2112Adapter
if dev := INA226Device.set_i2c_adapter(CP2112Adapter).open():
with dev:
dev.set_shunt_resistance(.015)
dev.init()
while dev.is_connected():
if data := dev.query_raw():
print(
dev.get_value(data, dev.CURR_CHAN), dev.get_mode(data, dev.CURR_CHAN),
dev.get_value(data, dev.VOLT_CHAN), dev.get_mode(data, dev.VOLT_CHAN)
)
else:
breakThe INA228 provides addition temperature measuring capabilities. One can even connect K-type termocouple to it instead of the shunt. The following code example illustrates reading voltage, chip temperature and termocouple temperature with such setup. It also illustrates using I2C adapter GPIO by blinking green LED on the CP2112 adapter board.
from ut61xpy.adapters.ina import INA228Device, CP2112Adapter
import cp2112
led_pin = cp2112.GPIO_LED_GREEN
if dev := INA228Device.set_i2c_adapter(CP2112Adapter).open():
with dev:
dev.init()
cp2112.gpio_config(dev.dev, led_pin)
led_on = True
while dev.is_connected():
if data := dev.query_raw():
print(
dev.get_value(data, dev.VOLT_CHAN), dev.get_mode(data, dev.VOLT_CHAN),
dev.get_value(data, dev.TEMP_CHAN), dev.get_mode(data, dev.TEMP_CHAN),
dev.get_value(data, dev.KTC_CHAN), dev.get_mode(data, dev.KTC_CHAN)
)
cp2112.gpio_set(dev.dev, 0 if led_on else led_pin, led_pin)
led_on = not led_on
else:
breakThe I2CDevice base class adds an important method to its descendants - attach_to_i2c_bus. It creates device instance by attaching it to existing I2C bus given the initialized instance of another 'master' device already sitting on the bus. No USB device discovery is necessary for the new device creation. It just uses already initialized USB device of the master. This method is useful in case you are going to read data from multiple devices sharing the same I2C bus and USB adapter. The following code example illustrates reading the data from ADS1115 and MCP3421 devices sharing the same bus.
from ut61xpy.adapters.ads1115 import ADS1115Device
from ut61xpy.adapters.mcp3421 import MCP3421Device
from ut61xpy.adapters.i2c import FT260Adapter
if dev1 := ADS1115Device.set_i2c_adapter(FT260Adapter).open():
with dev1:
dev1.init(2)
dev2 = MCP3421Device.attach_to_i2c_bus(dev1)
dev2.init()
while dev1.is_connected() and dev2.is_connected():
if (data1 := dev1.query_raw()) and (data2 := dev2.query_raw()):
print(
dev1.get_value(data1, 0), dev1.get_mode(data1, 0),
dev1.get_value(data1, 1), dev1.get_mode(data1, 1),
dev2.get_value(data2), dev2.get_mode(data2)
)
else:
breakNote that devices sharing the same bus should have different bus addresses to avoid conflicts. The MCP3421 has bus address programmed on the factory so its hard to have more than one such device on the bus. The ADS1115 may be configured to use 4 different addresses so you can attach 4 such devices to the same bus. Look at the particular device datashit for more details.
By attaching external multiplexer to ADS1115 you can create device able to measure multiple voltages sequentially. The example of such device is shown below. It is capable of monitoring voltage in 16 input channels.
The example schematic uses resistor dividers to translate input voltage either positive or negative to the range acceptable for ADS1115 (within its power rails). The following code example illustrates sampling input voltages with such device:
from ut61xpy.adapters.ads1115 import ADS1115Device
from ut61xpy.adapters.ads1115_mux import *
if dev := ADS1115Device.open():
with dev:
dev.init()
while dev.is_connected():
print(
mux_read_positive(dev, channel=0, div=.5),
mux_read_negative(dev, channel=3, div=.5)
)See ads1115_mux.py for more implementation details. Note that ADS1115 has finite input impedance of ~10 MOhm. Therefore to keep measuring accuracy within 0.1% the R0 value should not exceed 10kOhm.
If you don't need exceptional precision, then all multimeters with 6000 counts and more will give you reasonably good results in any mode except for the current measuring. Here we will consider why the current measuring mode is so demanding and why popular UNI-T multimeters are actually the least usable models for this task.
The multimeter does not measure current directly. It does measure voltage across current sensing resistor aka shunt. This voltage is effectively subtracted from the voltage in the net where you are measuring current. Suppose you are interesting in the current being consumed by microcontroller powered from 3.3V. If the voltage across the shunt is 0.5V then only 2.7V is left for microcontroller. This may affect it seriously reducing the current or even prevent microcontroller from working normally. Therefore, it is generally not desirable for the shunt voltage to exceed 100mV, which can be considered safe and should keep the current disturbance level at 3% (0.1/3.3). In practice many multimeters have full scale voltage across their shunts larger than that. For comparison I have made a table listing shunt resistance and full scale voltage for various multimeters including ones without PC interface, with manual ranges and even old analog multimeters with moving physical needle as display device.
Typically all multimeters have ranges with upper limits separated by a decade. Old multimeters have corresponding shunt resistances separated by decade as well. So if you hit the upper limit of the current range you may switch to the next range where the shunt resistance and so the voltage becomes 10 times smaller. The modern DMM simplify this schema by grouping sub-ranges into the modes (µA, mA, A) each with its own shunt. Each mode typically have two sub-ranges so that the shunt resistances are separated by two decades. If you hit the upper limit of the smaller sub-range, then you may switch to upper sub-range but this does not change the shunt voltage since both sub-ranges are using the same shunt. If the shunt voltage becomes too high, then the only option you have is to reduce it by the factor of 100 by switching to the upper mode, for example from mA to A. This approach places high demands on the resolution of the shunt voltage measurement.
Each multimeter may be characterized by the shunt voltage measuring resolution. Suppose the DMM has this resolution equal to 10µV as most 6000 counts models typically have. This means that given the shunt voltage limit of 100mV you have at most 10000 counts regardless of the total counts of your multimeter. But if you hit the 100mV limit and switch to the upper mode, then you will have 100 times smaller number of counts. That is with 10µV resolution you will have only 100 counts in the worst case. That's why for the best current measuring accuracy without rising shunt voltage to unacceptable level you need 1µV resolution. It will give you 1000 counts with 100mV shunt voltage in the worst case.
Surprisingly there are no multimeter model that works well in all its measuring modes. At least among models with PC interface withing 100$ price range. So you can choose between mostly good and unusable models.
- OWON XDM1241 is the best budget DMM with some reservations. Its not quite portable, slow and has almost unusable capacitance measuring mode. Besides its never switching itself off draining batteries with 1.2mA current while pretending to be switched off. Choose it if you don't need portability, long battery life and don't bother measuring capacitance under 1nF. The battery drain may be easily fixed by adding custom mechanical power switch.
- OWON OW18E is the best portable DMM with only one annoying drawback - the dead band from -5µV to +5µV where input voltage always reads as zero. Choose it if you need portability, long battery life and can tolerate dead band. Note that fortunately there are no dead bands in its current ranges (in contrast to UT61E+, see below).
- INA226/228 modules provide 64k and 1M counts respectively with fixed voltage range and current measuring range depending on the shunt resistance. The INA228 even has two software-switchable current ranges, providing the shunt voltage resolution by the order of magnitude better (smaller) than the best multimeter models considered above. It also can measure temperature with external K-termocouple with high resolution.
- The popular UT61E+ has 5 Ohm shunt resistance in mA mode which is quite high and limiting. With current exceeding 20mA you will get the voltage drop exceeding 100mV. So the 220mA range is almost unusable since it gives maximum voltage drop of 1.1V. Therefore to measure currents above 20mA the A mode would be preferable in theory. In practice though you will hit two fatal surprises there. First, the only A mode range is 20A with 1mA resolution, so the resolution drop is 3 orders of magnitude compared to 22mA range. Second, there is a dead band in A mode from -5mA to +5mA where current always reads as zero. Therefore the UT61E+ is almost unusable for measuring current in the range from 20mA to amperes which is typically the most common case. Interestingly, the cheaper UT61D+ model does not have these problems. It has lower shunt resistance (1 Ohm in mA mode) but the shunt voltage measurement resolution is 2 times higher - 10 µV.
- Another UNI-T model, the UT60BT has interesting feature - the recoverable PTC fuse in µA socket. It looks convenient but adds 3.3 kOhm to the shunt resistance which is only 45 Ohm. This makes it absolutely unusable for measuring small currents. To complement it, the A mode has a dead band from -5mA to +5mA. So its hard to recommend it for measuring current in any range despite excellent 1µV voltage measuring resolution. The voltage mode is also spoiled by dead band from -10 µV to +10 µV. Therefore I would say its the least usable device of all.
The above discussion of UT60BT multimeter demonstrates that the resistance of the fuse may affect the overall resistance across current and common terminals significantly. Even for the melting fuse commonly used in mA terminal circuit its about 0.6 Ohm which is not small compared to the typical shunt resistance of 1 Ohm. The fuse resistance cannot be made smaller since it should be able to produce enough heat to melt itself. Therefore actual resistance and so the voltage drop is always higher than the values shown in the comparison table.