Schematic of the Arduino Solar Tracker Circuit. As you can see in the schematic all that you need to make the electrical part is the board, one servo, 2 LDRs and 2 x 10K resistors. Usually the servo ...

His test circuit uses six 2N2222 transistors to protect the Arduino from excessive current. You can see six red LEDs above which are inline with the base of teach transistor.

Because students are using it, it needs to be short-circuit-proof – no possibility that a mix-up in control signals can cause the drive to short out the rails (see DANGER, right). BTW, don’t use these ...