I put together this Voltage Unit (VU) meter using LEDs on a breadboard the other day. It only has 4 LEDs, but can easily be expanded to more:
It’s basically a simple display for showing a value. It’s originally for showing signal level in audio circuits, but there’s no reason you can’t use it to show temperature, rain intensity, light level, or whatever other value you are measuring.
In the video above, I added a potentiometer as a voltage divider between 9V and 0V, so that the output would be somewhere in between. This way I could easily test the VU meter.
If you want it to show audio level or any other signal with very low voltage, replace the potentiometer with an amplifier.
Here’s the circuit diagram:
The Qs are NPN transistors. I used BC547.
D1-D3 are standard diodes. I used 1N4007.
R1 to R4 are there to limit the current to the LEDs, and I used 1k.
R5 to R8 are there to limit the current through the transistors. I forgot what I used, but anywhere from 1k to 10k I think should work.
The potentiometer I connected between 9V and 0V. And the middle pin I connected to the “Input Voltage” port.
If you want this, but think there are too many components, an alternative is using the LM3914 IC.
Have you built this circuit or something similar? Let me know in the comments below!