There are a great many heating elements on the market but most require a great deal of energy to provide heating. And most of those products are way too much for the needs of the Maker.

The Adafruit 10cm x 5cm heating pad is different. Apply 5-12VDC and the stainless steel fibers in the heating fabric will warm up, creating a little heating pad. On one hand, it's just a gigantic resistor. On the other hand, it's flexible, light, and can be wrapped around a project. Originally designed for portable wearable heating pads, the fabric can be used for wearables, weather balloons, diy-bio projects, thermal cycling for materials testing, etc.

The benefits of using this pad:

• It can be controlled by lower voltages
• It can be pulse-width modulated to control temperature
• It is flexible for many projects

Ok, time to think electrical. The data sheets for this pad say that at 5 volts, the sheet may require 740 milliamps (0.74 amps). The Motor block can source up to 1 amp (1000 milliamps) which will work fine. We can control the power getting to the pad via pulse-width modulation as the motor throttle. Other things like direction will not have any bearing on how the pad works.

The Drive port of Crickit is good for up to 500mA, so the Motor port is a better pick here, to get the most power output.

Hook Up

A potentiometer (variable resistor) center pin is connected to Circuit Playground Express pad A7, the outside potentiometer pins connected to 3.3 V and Ground. This provides a variable voltage which can be read via the Circuit Playground Express Analog In.  The programs will read this to determine how much it should drive the heating pad. 

A TMP36 temperature sensor is connected to Circuit Playground Express pad A3 with power and ground to sense the temperature. If you'd like to learn more about the TMP36, see this guide for details.

The code is on the following pages in MakeCode and CircuitPython.