This guide will help you to find and fix any issue with the Arduino Audio Meter hardware.
I have to say that 99% of the problems are due to silly mistakes that can be found with a careful visual inspection (take your time).
Before doing any serious troubleshooting just try to re-touch with the soldering iron ALL the solder joints, it is pretty easy to get a (disconnected) cold joint, especially in the header or op-amp socket (also try unplugging and plugging the op-amp, sometimes one of the legs is not making contact). Re-heat the components solder joints to have perfect connections.
If you only have problems with the 8x8 displays, have a look at the 8x8 troubleshooting topic:
Top 3 Silly Mistakes:
Audio Connections: This pedal is designed so the input and outputs are interchangeable. It does not matter where you connect your gear:
Make sure that the RV1 potentiometer is in a good position. This trimmer resistor adjusts the input audio signal going into the pedal. Having it in the middle position (the notch facing up) is a good starting point for any guitar, it has a logarithmic attack, that means that at the beginning of its travel, the pot does not add much gain nut in the last quarter of the travel it can give loads of gain.
Electrolytic Caps or op-amp placed wrong: Have a look to a good PCB in high resolution and check that you have yours in the right orientation. It is quite common to place the op-amp upside-down
Check any short circuit between nearby pads and check that all solder points are good.
Now, the best way to troubleshoot the Arduino Audio Meter is following these 4 steps:
1. Check the power supplies: This step is usually a key factor. Make sure that you have similar voltages to the ones showed below:
note: to make these readings, just use an external DC power supply and do not connect anything to the input and output jacks.
2. Check the input stage: With a multimeter make sure that you can read the voltages listed above on the operational amplifier.
You can also check connectivity: With a multimeter check that the tip of the guitar pedal is connected to C1, also that the other side of C1 is connected to the op-amp pin 5. Make sure that R4 is connected to the pin A0 on your Arduino UNO board.
3. Check your Arduino UNO board. Sometimes there are some Arduino UNO boards that do not work properly and can drive you crazy.
Load a simple code to blink the LED: www.arduino.cc/en/Tutorial/Blink
As a tip I can to say that 99,9% of the errors are due to some connection is wrong or some component is misplaced. From previous experience building dozens of pedals they always work straight away from soldering correctly, but we are all humans and we all make mistakes.
If all the above fails, just carefully component by component that it is well placed and orientated, don't take anything for granted.
If you can borrow another pair of eyes to have a look at it, do it. Sometimes others can easily see things that we are passing over.
If you have an oscilloscope and a signal generator (I use Visual Analyzer) you can trace a sinewave from the input jack -> op-amp input -> op-amp output -> input ADC.