#181 VoltmeterModule

Test a 3-wire voltmeter module

Notes

I obtained a 3-wire voltmeter module as part of a kit, so a chance to test one out!

There are two and three wire modules in the market.

Two-wire modules are the simplest (and generally cheapest). For most applications where a simple readout of a power supply is required, they are most convenient since a separate power supply connection is not required. It does mean of course that the meter draws current from the circuit under test, and will only work down to a certain voltage (usually ~4.5V).

For more precision measurement, the three-wire modules are better suited:

• they present relatively high input impedance (> 100kΩ)
• can measure voltages from 0V and up

I can’t find a specific datasheet for the 3-wire module, but from product listings, the specifications are as follows:

• Measuring range: 0~30V;
• Power supply: DC 4.5~30V;
• Max. input: DC 30V;
• Tolerance: +/-1%, +/-0.3V (>=10V), +/0.1 (<10V);
• Input impedance: >100Kohm;
• Working current: red: <23mA;
• Refresh rate: 300ms;
• Display: 3-digit 0.36” LED;
• Display color: red;
• Cable length: 15cm

These modules do not have any kind of digital output that could be used to integrate with a microprocessor, but as a stand-alone meter, a useful device for power supply circuits.

Test Circuit

Schematics below are for a simple test of the meter using a 10kΩ pot to vary the input voltage and compare the reading with a multimeter.

Using my DMM as a reference, it appears accuracy is within 40mV, good enough for general purposes.

Construction

NB: the Fritzing part used here is not quite right (it’s actually a 4-wire ammeter) but does well enough for a simple schematic:

Credits and References

• DSN-DVM-368L-3 3-Digit 0.36” LED Digital DC Voltmeter - example product listing on dx.com
• Mini DC 0-100V Yellow LED 3-Digital Display Voltage Voltmeter - example product listing on aliexpress
• ..as mentioned on my blog