Ultimate Raspbian

I almost abandoned the whole project in order to come back to my world of ones and zeros where EVERYTHING WORKS. It seems that my PN2222A transistors are from a rare manufacturer who is not respecting the datasheet because the emitter-base-collector has other order, but first things first.

Right after having the car kit mounted, I tried to move a wheel with a transistor powered by the Arduino. To do so, I checked many schemes, but in all of them it was always the same: the engine was always at full speed, not being affected by the base pin, no matter if it was ground, 5V or PWM. I tried everything:

• Schemes where the order with the flat side up was emitter-base-collector, like the one in the exercise 17 from the pdf included in the Arduino starter pack that I bought to my father. By the way, in the PN2222A datasheet the order is emitter-base-collector.
  
• Schemes with a 2N2222 transistor where the order was collector-base-emitter (link here).
  
• I tried more stuff that I can’t and don’t want to remember, I just didn’t care anymore.

A lot of things could have been failing or burnt, so I started checking from scratch to find the source of the problem. I learned a lot about transistors with this web and after 2 sheets of maths I understood much better how it should work. I also tested a basic PWM circuit to power a led in order to discard that the PWM, 5V or GND pins weren’t working anymore, luckily that was not the case, so the problem was not in what I was sending through the transistor base.

When everything was lost I researched how to check if a transistor was burned. I found some websites saying the same: if you put a voltmeter lead in a pin and you check resistence to the other two pins getting values different from “Over Limit”, then this first pin was actually the base. I made every possible combination and there was no doubt: the base was in the first pin!, also according to this website, the transistor was PNP.

Conclusion: the datasheet says that PN2222A transistor is NPN and the order is emitter-base-collector, but the PN2222A included in my Arduino starter pack is PNP and order base-collector-emitter.

In the next iteration I’ll finally manage to freely move the engine.