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Project Notes

#289 Voltmeter/Ammeter Module

Test and calibrate a DC Voltmeter/Ammeter panel module.



I got this DC 0-100V 10A Digital Voltmeter/Ammeter module from a seller on aliexpress at a nice price. But is it any good?

This project is a quick test of the unit. Bottom-line: not bad for an easy voltage/current indicator. For more accurate readings, it is a good idea to check the calibration.


  • Display color: Red (voltage) & Blue (current) LED dual display.
  • Display: 0.28” LED digital.
  • Operating voltage: DC 4.5 ~ 30V (for power supply to the module)
  • Operating Current: <20mA.
  • Measure voltage: DC 0 ~ 100V.
  • Minimum resolution (V): 0.1V.
  • Measure current: 10A (direct measurement, built-in shunt).
  • Minimum resolution (A): 0.01A.
  • Measure accuracy: 1% (± 1 digit).
  • Refresh rate: ≥500ms / times.
  • Operating temperature: -10 to 65°c.
  • Operating Humidity: 10 to 80% (non-condensing).
  • Size: 48mm x 29mm x 21mm.
  • Mounting cutout: 45.5mm x 26.5mm.

Here is the module, front and rear. Unfortunately it is not possible to determine what kind of processor is used, as the main IC has no markings



Module Power Supply

The module takes a separate power supply to drive the unit and LED display. This is good, as it avoids confounding measurements of the circuit being monitored with the unit’s own power requirements, and allows voltage measurement below the minimum 4.5V required to power the unit.

It’s important to note two things:

  1. the module power supply shares a common ground with the circuit under test, so care is required with the arrangement of external circuitry to avoid a ground short

  2. the 2-pin JST power connector has the opposite polarity from what is commonly seen in JST power connections. There is no actual standard, so this is not a problem per se, and the supplied connector lead is correctly colour coded. But if other power connectors are used, it is important to double-check polarity

External Circuit Wiring

Connecting the module in-circuit simply requires:

  • parallel connection to the positive voltage supply (red wire)
  • series connection on the low-side of the load to ground (blue, black wires)


Test Load

To run some tests, and in the absence of anything better, I mocked up a dummy load:

  • 12V, 1.5A, 18W DC power supply
  • an arrangement of parallel 50Ω 5W resistors. I connected between 1 and 5 of these for different static resistive loads
  • a 9V battery to power the module independent of the load


Initial Test Results

It works nice enough, but is not quite as accurate as the claimed 1% (± 1 digit) resolution (i.e. the last digit can be off by one). The unit is obviously not suitable if you need accurate mV and mA readings.

Load Nom Voltage Nom Current Nom Power Measured Voltage Measured Current
50Ω (1) 12V 240mA 2.88W n/a n/a
25Ω (2) 12V 480mA 5.76W n/a n/a
16.7Ω (3) 12V 719mA 8.62W 12.5V 0.69A
12.5Ω (4) 12V 960mA 11.52W 12.5V 0.93A
10Ω (5) 12V 1.2A 14.40W 12.5V 1.17A


  • I didn’t take measurements for the 1 and 2 resistor gangs
  • nominal power per resistor is 2.88W, that’s why I’m using 5W resistors here.
  • according to my multimeter, the power supply delivering about 12.3V over 50Ω down to 12.05V over 10Ω. Still, readings not quite within 1% resolution.
  • resistors are quite close to their 50Ω rating. Five in parallel measure at 10.3Ω according to my multimeter.

So Does it Just Need Calibrating?

There are two trimpots on the circuit board. Although not documented, it’s highly likely they are fine adjustment for voltage and current measurements. And indeed they are:


With a bit of adjustment, I’m now getting results within the 1% (± 1 digit) range. Here it is with a 10Ω load over 12.13V:






Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.