I have a 5v USB heating pad which I hope to use to over-winter a tropical seedling. The Spec Sheet implies the pad heats to50degrees. Would appreciate advice as to how to control at about 20-25degrees. Thanks IANO
For any sort of accuracy I imagine you would need to create a feedback loop that switches the pad on when it drops below 20 degrees, and off when it rises above 25 degrees.
You’d need some way to switch the pad on/off to accomplish this, and I imagine if it plugs directly into a USB port that would mean either:
a. cutting off the USB connector and stripping the wires
b. Use something like this to connect it - https://shop.pimoroni.com/products/sparkfun-usb-type-a-female-breakout
Then you’d need a relay, or perhaps just a darlington driver depending on how much current the pad consumes, and a basic temperature sensor to create your control circuit.
Alternatively. There’s an argument for trying to pass a constant 3v or 4v through the pad and seeing if it hits a relatively constant temperature in your desired range- if you have a multimeter (or if the spec sheet details it) you should measure the resistance of the pad, this information should allow you to pick an appropriate additional resistor to form a voltage divider.