Comments: Heating Pad Hand Warmer Blanket

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  • Can someone explain what the 10k resistor between the source and gate is for? I wired up the schematic without the resistor but the MOSFET seems to always be on…

    • It’s actually there to prevent this exact problem! With the resistor in place, the gate is pulled low (off) all the time. When the Lilypad pulls pin 3 high, (on) the Lilypad overcomes the weak grounding effect the resistor presents and th MOSFET turns on.

      MOSFETs are so sensitive that any stray static electricity in the air can trigger them so we use the resistor to ‘ground’ any static charge that may be nearby and keep the MOSFET off until we want to turn it on.

  • Hello, I have a couple of these and was wondering if it was possible to use an LM35 (or similar) to measure the temp and then switch the pads on/off if above/below a certain temp? Totally new to electronics :)

  • Thank you so much!! That fixed it!! Thanks for the quick response!!

  • I’m having a problem with the example code for the Hand Warmer Heat Pad. This line “ mode = mode == 3 ? 0 : mode + 1;” says “‘mode’ was not declared in this scope”. Anyone found this out also? Thanks.

    • Looks like the example code was missing a variable declaration. If you add int mode; near the top, right under the int led3 = 11; line, that should fix it. The example code has been updated as well.


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