Be sure to not have flammable material or skin on the heating pad during testing and use.

In use, the pad will be at room temperature (with the potentiometer reading 0 on the serial monitor, meaning the pad is off) to a measured 129 degrees F / 56 degrees C with the potentiometer fully on.

The center of the pad seems to gets hotter than the edges but make measurements around the pad to check for even heating.

Do not expect the pad to go from cold to hot quickly. The resistive material in the pad does not act quickly, it may take 30 seconds or so to adjust to temperature change requests.

If you want something more instantly hot or cold, the Peltier module in the next section may be what you need.

As you turn the potentiometer, the pad should warm up. If you press the Plotter button in Mu for the CircuitPython version, you should see the temperature rise on the temperature sensor as you turn the potentiometer but it will not rise fast.

These are the readings you will find with this setup:

Pad Fully On, Crickit outputs 4.49 volts, 670 milliamps, just over 3 watts
Bypass Crickit, pad connected directly to 5 volts: 5.12 volts, 740 milliamps, 3.79 watts

These are readings with a multimeter and non-contact thermometer. The TMP36, when used to measure the temperature, should be affixed in direct contact near the hottest place on the pad if possible.

Application

This type of setup would be very good for remote control of heating in an outside electronics enclosure where you don't want the enclosure contents to get too cold. You could monitor the temperature and vary the heating accordingly.

This would not be the best way to heat ones drink. You should plan your temperature range to fit the capabilities of the heater element.