Test a 3-wire voltmeter module
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.
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.
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