I have a solar panel and i want to make a program that measures how man volts it is giving off at a certain time. When I put my solar panel toward the light my voltage measurer says that it is giving off 3 volts. My solar panel has a red wire and a black wire. Where do I connect them and how do i program it.

Measuring voltage is pretty easy but you need to be careful that you do not pump higher voltages into the processor A/D than it can handle.

If you have built the thermometer circuit, you have most of it already in place.

Remove the LM34 from the circuit and use pin 23 for your input, (red wire). The black wire will need to connect to the negative rail, or ground. If the voltage never exceeds 5V, you wouldn't need to do anything else to the circuit. All you will need to do is fiddle with the math part of the program to reflect the actual values you are measuring.

If you are measuring voltages above the 5V limit, a voltage divider circuit will be necessary to avoid causing damage to the chip.

There is another message thread that also discusses a similar topic but I couldn't tell the title from memory.