#181 DC Voltmeter Modules

Testing a selection of 3-wire DC voltmeter modules.

VoltmeterModule_build

Notes

There are two and three wire DC voltmeter 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

Modules tested below:

Module 1: DSN-DVM-368 v3.01. Screw mounted with no bezel, measures from 0-30V
Module 2:

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.

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:

Breadboard

The Schematic

Module 1: DSN-DVM-368 v3.01

This is a common type of module that is screw mounted with no bezel and can measure from 0-30V.

I think I originally obtained this module as part of a kit, but they are widely available from parts sellers:

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

front rear

I can’t find a specific datasheet for the 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: >100KΩ;
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.

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

module01_test

Module 2: 0.56” Panel Meter

This is a common panel mount module with 0.56” digits and can measure from 0-100V. Other versions are available with different measurement ranges: 0-10V, 0-30V, 0-200V.

They are widely available from parts sellers, e.g.:

0.56” 3 Wire Digital LED Voltmeter Voltage Meter Panel with Reverse Protection DC0-100V (Red) - aliexpress

module02

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

Test voltage range: DC 0-100V
Accuracy: 1%
Display: 3 digits LED
Working temperature: - 10 ~ + 65℃
Measurement rate: 200mS/time
Power: DC 3-30V
Max. output: DC 100V (above 100V carries a risk of burning)
Min. output: DC 0V (Below 0V, measurement inaccurate or not shown)
Current consumption: <20mA
LED color: Red/Blue/Green/Yellow (Optional)
Weight: Approx.17g/0.6oz
Size: Approx.4.82.91.9cm

Tests reasonably accurate:

module02_test

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