We'll build our own sensor bar to read the track steps. We'll use five sensors. The IR sensor packages contain two small elements, an IR LED and an IR sensor enclosed in a plastic housing.
You can ignore the leg lengths (short leg doesn't mean ground in all cases) and instead use the diagram to orient things properly.
The IR LED is the clear element. It will receive power from the Crickit's 3.3V line, with a 220 Ohm resistor to reduce the voltage. The dark element is the IR phototransistor. It will send a signal to one of the Crickit's Signal input pins, using the internal pullup resistors of the Crickit. Both are tied to ground.
You can build this on a breadboard for testing; ultimately we'll solder it onto an Adafruit Perma Proto board.
We'll also connect the Perma Proto board's two ground rails with a jumper wire.
Lastly, run a color coded jumper wire from each sensor's signal leg to the associated pin coming from the cable interconnect as shown. Solder these in place and our sensor board is ready for use!
Now, plug the cables into the Crickit's Signal I/O ports as shown.
Place the speaker wires into the two speaker terminal ports on the Crickit and screw them down firmly. You may need to strip a little extra insulation from each wire first to get a better connection.
Plug the continuous rotation servo cable into the Servo 1 port on the Crickit with the orange wire nearest to the outside edge of the Crickit.
Plug the 5V 2A DC power adapter plug into the Crickit's power barrel jack.