Advance Preparation
and Setup

To avoid having the students solder, set up the circuit with alligator clip leads. If you use the side-by-side AA battery holders, then in advance you can solder the 47 ohm resistor to the negative (black) lead from the battery clip (the same battery clip that fits a 9-V battery). If instead you use C or D cells in the usual holders, wire the batteries in series with the alligator clip leads. When you wire the phone plug, use bell wire so you can fasten the wire to the alligator clips. If possible, hook up an oscilloscope to the signal on the speaker.