Background
Often times you need to determine the polarity of a battery in the event that the + and – markings are unclear. This circuit probes a battery and determining and illuminates a green or red LED to indicate the correct polarity.
Schematic
The zener diodes are used as voltage regulators.
NOTE: D3 is a green LED indicating that the polarity of the DUT/EUT is correct. D4 is a red LED indicating wrong polarity
Here’s me testing a big battery that I salvaged from a kid’s car:
In Closing
For a version 2.0, I want the following additions:
- Display of battery voltage either using an LED bargraph or 4-digit 7-segment display
- A buzzer for introducing an audio cue
- Brighter LEDs for easier illumination