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I'm using a Raspberry Pi to control an ESC and would like to be able to turn it on and off at will using a TIP3055 NPN transistor.

I've hooked everything up as diagrammed below. The 11 V battery runs through a distribution board that provides several 11 V lines and a regulated 5 V line which will power the RPi in the future. As for now, it's powered via a separate USB connection.

If I manually disconnect and reconnect the wire to GPIO20, the transistor works as expected. If I leave the wire connect and turn the pin on and off with software, the ESC maintains power the entire time. I thought maybe power was being forced from the transistor to the GPIO pin (as the wire reads ~2 V when connected) so I put a diode between the resistor and the pin but that had no effect.

At this point I'm fairly certain that I shouldn't have used this particular transistor. I believe I should have put in a MOSFET but I wasn't clear on what I was doing when I started.

Aside from "mostly everything" what do I not know that is not letting me set this up correctly?

circuit diagram

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    \$\begingroup\$ Is this a complete schematic? Am suspecting there's some missing connections regarding RPi ground. \$\endgroup\$ – glen_geek Aug 7 '17 at 13:31
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    \$\begingroup\$ @pipe I thought it was the wrong way too at first glance, but it makes sense when you think about it. \$\endgroup\$ – Harry Svensson Aug 7 '17 at 13:40
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    \$\begingroup\$ @HarrySvensson they currently do not. The Pi is being powered via a separate USB connection. \$\endgroup\$ – castis Aug 7 '17 at 13:42
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    \$\begingroup\$ @castis no it's pointing the right way, it's just a very odd way to put it, usually the arrow points downwards or to the right, left is.. it's like seeing a car in england. "Oh no, they are driving on the wrong side". \$\endgroup\$ – Harry Svensson Aug 7 '17 at 13:43
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    \$\begingroup\$ Well then, if they are not sharing ground, then there's your answer. I'm aware that you're powering the RPi with USB, but you can still solder a ground line from the USB and connect it to the battery's negative pole to form a complete circuit with the ESC & NPN & control signal. \$\endgroup\$ – Harry Svensson Aug 7 '17 at 13:43
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These are the basic ways of switching using either PNP / P channel MOSFET for high side switch or NPN / N channel MOSFET for a low side switch.

At all times the ground (0V) of the battery and the rpi are common.

enter image description here

Note: R5 (1k0) is optional but is a useful if using a Darlington NPN (high gain) as it helps to pull down any leakage current through the PNP.

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    \$\begingroup\$ I love looking at the low-side pics. It's like a giraffe, with the tall neck reaching up to its head at the PNP, where the voltage vistas are "high up" in the tree tops, which then is looking back down at the power device. But a necessary arrangement given the voltages involved. \$\endgroup\$ – jonk Aug 7 '17 at 15:50
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    \$\begingroup\$ @jonk, Whatever your drug dealer is hooking you up with, I want in on it. :-D \$\endgroup\$ – winny Aug 7 '17 at 16:10
  • \$\begingroup\$ @winny Hehe. It's just how Jim's pic looks. You can see the body with its feed "grounded" (planted), and it's long neck rising up. Hard to miss, the way the pic is done! And I like to imagine the high tension above the RPi as being "high up" like the tree tops might be on a savanna. Too high for the RPi to reach. But not too high for the giraffe! ;) \$\endgroup\$ – jonk Aug 7 '17 at 16:35
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    \$\begingroup\$ @jonk I know who's "high up" alright. \$\endgroup\$ – winny Aug 7 '17 at 16:38
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    \$\begingroup\$ @castis One problem with the 3055 NPN in particular is that it can take close to 1 A through the base to get it to drive 15 A. That's something to think of when trying to drive it with a simple I/O... \$\endgroup\$ – pipe Aug 7 '17 at 17:57

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