The OEM33 is one of the world's smallest digital voltmeters. It is an ideal replacement for analogue meters with advantages of accuracy, size and easy mounting.
The OEM33 is a 3.5‑digit LCD digital voltmeter module designed for easy replacement of analogue meters. It offers a 10 mm character height LCD, 200 mV full‑scale sensitivity, automatic zeroing, polarity indication, 11 selectable annunciators and a display‑hold facility. The module includes an A/D converter, LCD, and a plastic housing with dual‑in‑line pin terminals for PCB mounting.
The device can be powered from either 5 V or 9 V supplies (incorrect polarity will destroy the module). Connections are made via dedicated pins for supply, ground, hold, annunciators and decimal‑point selection. Detailed specifications such as input impedance, reference voltage, overload voltage and temperature limits are provided, along with wiring diagrams for both 5 V and 9 V operation and example application circuits for voltage and current measurement.
| Resolution | 3.5 digits |
|---|---|
| Full‑scale sensitivity | 200 mV |
| Supply current (9 V) | 500 pA typical |
| Input impedance | 100 MΩ |
| Reference voltage | 100 mV (9 V supply) |
| Overload voltage | 20 V |
| Resolution (minimum step) | 100 µV |
| CMRR | 70 dB |
| Temperature coefficient | 150 ppm/°C |
| Operating temperature range | 0 °C to 50 °C |
| Storage temperature range | -20 °C to 70 °C |
| Panel cut‑out size | 40.5 mm × 22.5 mm |
| Acceptable panel thickness | 0.9 mm to 3.2 mm |
The OEM33 can be powered from either a 5 V or a 9 V supply; applying the wrong polarity will destroy the module.
An over‑range is shown by displaying a “1” in the most significant digit of the LCD.
Apply 100 mV to the inputs from a calibrated source and adjust VR1 until the display reads 1000.