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Timeline for Transistor switch without polarity

Current License: CC BY-SA 4.0

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Aug 15, 2018 at 9:29 comment added Keith Burk Thanks for the explanation Henry! I set each circuit up to control 8 props. I also built in a master and slave functionality to allow boxes to be daisy chained together for scalability.
Aug 15, 2018 at 5:10 comment added Henry Crun @KeithBurk How many props do you need to control from one arduino?
Aug 15, 2018 at 2:29 comment added Henry Crun If you look at an npn transistor, there are two diodes "pointing" from the base. One is B->E. The other is B->C. Both of them can work to turn on the transistor. Except the proper B->E base is 10x more gain. When you swap C and E gain is very low. You can test this by seeing how much current flows through it from 5V with a meter, then swap C&E. This is working because (most) of your props are only needing a very tiny switch current to turn on, so it doesn't matter. (I didn't suggest this because it is dodgy - even for me)
Aug 15, 2018 at 2:13 comment added Keith Burk Thank you team optocoupler! I had a 4N35 optocoupler hanging around from an Arduino starter kit that I bought a few years ago but never had the opportunity to experiment with. I connected pin 1 to VCC through a 1k ohm resistor, pin 2 to an ATMEGA328P-PU digital output pin, and my prop's VCC and GND to pins 4 and 5. All 5 of the props that I checked both ways (reversing pins 4 & 5) triggered irrespective of polarity. I still have some research to do to understand why it works but I greatly appreciate all of your insight to point me in the right direction!
Aug 14, 2018 at 11:22 comment added Henry Crun I would probably start with a simple opto, and put the optos inside the props - running long wires from the random circuitry is going to cause more problems than running 5V to the opto leds. It should be no problem to workout the switch polarity when you modify the prop: one way it works, the other it doesn't.
Aug 14, 2018 at 11:18 comment added Henry Crun If you are hooking things with power adaptors together, then there are small current and quite high voltages between them. It makes connecting transistors to ill defined circuits an unreliable proposition. Having clean isolation (optos) avoids that. I was surprised on aliexpress that plain 4 pin optos are 3c each. Probably not the best, but I doubt you care. Using a pair of them is only 6c, and actually not to hard to just wire directly to if you are good at soldering.
Aug 14, 2018 at 9:48 comment added Keith Burk Thanks Henry! My understanding of electrical components is limited so I'll have to do some research to learn how to execute your recommendations. A quick search on Digikey makes it seem as if H11AA1 costs about as much per piece as the relays that I'm trying to replace. Is there a bigger cost difference if ordered directly from China? In the second half of your post you say "if I really want to have problems". Is that sarcasm or a typo?
Aug 14, 2018 at 1:18 history edited Henry Crun CC BY-SA 4.0
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Aug 14, 2018 at 1:10 history answered Henry Crun CC BY-SA 4.0