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Thanks in advance for reading guys.

Last night I set up a circuit to see if I could heat up a resistor to about 60(ish) degrees C but do it with the resistor part of the circuit on paper. This circuit used circuit scribe ink on paper with a 220ohm resistor as connected to a breadboard which had a transistor with the following set up.

Base - RPI 3.3v from GPIO (pin 37) with a 1k resistor

Collector - 12V DC through to a DC Barrel connector (12 volts through 240ohms by my workings gives me 50ma which heats up my resistor just fine on other circuits). The Barrel had its switch pin and negative pin hooked to RPI ground pins.

Emitter - RPI ground pin

I had this circuit originally set up without the emitters resistor on paper and it worked just fine but once I connected jumper cables in and out of the paper circuit the Pi blew.

The wild card is that I stuck the jumper cables down with sellotape (which was in contact to the circuit), very stupid I know...

So did my Pi blow up because:

1- The sellotape did something strange with static?

2- I actually don't understand transistors and it some how fed the 12v back to my Pi? or do transistors always feed collector electricity to the base source??

I've uploaded a photo but if you would prefer to see a diagram I will draw one up and upload it.

Cheers,

Oli Circuit pic

  • What kind of transistor? WHY did you connect the emitter to 12V? This is just like connecting 12V via a diode to the GPIO! – Milliways Jan 26 '17 at 1:33
  • Sorry typo, emitter was to ground on Pi. – OliAus Jan 26 '17 at 1:59
  • And transistor was NPN – OliAus Jan 26 '17 at 2:00
  • ugh, fast blow fuses/fusible links/diodes for every line going to the pi... – Dan V Jan 26 '17 at 21:12
  • I was under the impression that the ground pins can handle a bigger current? So they should of been fine with grounding the 50ma from ththe dc power source. – OliAus Jan 27 '17 at 1:41

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