I'm glad to see your progress with this project... a very neat one by the way. As a simple suggestion, I think it's better to use a potentiometer in your voltage divider that will allow you to adjust the fraction of voltage you are going to feed to the OP Amps more precisely. This will simplify the code later on. Simply use 2 resistors as usually for the voltage divider; but place a pot with a resistance value around 10 times smaller than the value of the resistor connected to ground. Take the voltage from the pot wiper and send it to the opamp. This will allow you to precisely adjust the voltage fraction using 5% resistors instead of 1% ones. Easier to experiment with the divider set up that way.
Good Luck