The circuit uses a LM3914 this takes an input voltage and turns on a set number of LEDs dependent on the input voltage. In this case the input voltage is from the battery you want to test. Two resistors are used to set the number of LEDs to turn on at set voltages. As I have designed the circuit to test 3 battery voltages 1.5v, 3v and 9v. A DIP switch is used to select the resistors that are used.
I designed a PCB for the battery tester. The PCB is double sided with instructions on how to use the device silkscreened onto the front. All components can be soldered in place with help from the silk screen and schematic. You can secure the 9 volt battery holders with small bolts or hot glue.
How to use
To use the device simply insert a 9 volt battery into the battery holder in the top right of the PCB.
Once the circuit is powered chose what type of battery you want to test. Look at the silkscreened instructions and turn on the appropriate switch's. Then insert the battery and the LEDs will turn on. If the LED is green the battery is good if it is orange it is a bit low and if it is red then the battery is very low.
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