Here is more documentation from the tone labs.  I’m getting better at remembering the Arduino syntax so it didn’t take as long to troubleshoot this time.  I also got my hands on the correct  resistor (100 Ohm) for the speaker so now the sound is actually audible:

Here is a tone from two photocells in series acting as a variable resistor:

Here is the “3 note instrument” part of the lab.  I did not have three FSRs so for “keys” instead i have an FSR, the kit potentiometer, and two photocells in series acting as a variable resistor.

On my first try I got a continuous tone from the start and I did not understand why.

Then i realized that the threshold function was too low.  The lab told us to set it to 10, but after taking readings from all three “keys” I realized that the photocells read in the middle of their range when neither cell is covered.  So even though their range is from like 80 – 900, if there is no difference between the two they will stay between 450-600 (depending on the room). So I boosted the threshold to like 620 and the instrument was silent until i activated one or more of the sensors.  Here are two videos of that: