The circuit is nearly identical to the Make It Hot project earlier in the tutorial. Note the Peltier module connects to the Motor 2 connection where the heating pad had been previously. Be sure you power the Crickit from a 5 volt 2 amp (or greater amperage) power supply.
The TMP36 temperature sensor is connected to Circuit Playground Express pad A3.
The potentiometer center terminal is connected to Circuit Playground Express pad A7.
The Peltier Module is on Motor terminal 2 with the black wire towards the speaker icon and the red wire next to it.
The Crickit Motor terminals use pulse-width modulation (PWM) to quickly turn the connections off and on to vary what the device receives. This is perfect for devices like motors and resistive heating elements. But not so good here!
Peltier modules have solid state junctions that do not work well with fast on/off times like in PWM.
The modules can be turned off and on less quickly, a second or more. The CircuitPython and MakeCode programs on the following pages do exactly that, always having the "motor" throttle run either 0 (off) or 100% (full on) but switched by the program rather slowly on the order of seconds.
The potentiometer selects on on/off cycle time between 0 and 10 seconds. If the time selected via the potentiometer is > 0 then the code ensures that the time is at least one second. The entire cycle time was chosen as ten seconds. At the ends, zero results in full on, fully turned, the module is off.
The NeoPixels on the Circuit Playground Express show how strong the cooling is from no pixels (off) to 5 (half), to 10 (full on) and in between.