Speaker Amplification
A “Class A” amplifier arrangement works well to keep a quiet speaker output for activities and prevent large current draw:
Without the capacitor, the setup is louder. R1 can be dropped down to 470Ohm (for a 10.6 mA draw). For the final machines, the speaker can most likely be used with a direct connection to pin 13 for highest volume. We haven’t verified that this draws a safe current from that Arduino pin, but we haven’t broken anything either!