Electronics > Beginners

Help with troubleshooting simple transistor switch circuit

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yaun:

--- Quote from: magic on January 16, 2020, 11:09:06 pm ---BTW, what if you set the DMM to mA/µA range and short the camera with that? How much current does it pull from there?

--- End quote ---

200ma for the specific camera in question.

I've tested a variety of cameras and they vary between 50µa and 250ma. Most at 3.3v and one at 5v (not surprising I suppose).

yaun:

--- Quote from: magic on January 16, 2020, 10:55:00 pm ---So the transistor was somewhat leaky and passed the camera's current to ground even when off.

--- End quote ---

I'm not sure if I was unclear, but there is no camera in this circuit. The intention is to hook one up (and I have tested quite a few out of curiosity), but I'm concerned about the readings varying depending on the power supply.

magic:
200 or 250 mA :wtf:

I'm not sure if you have figured out those particular cameras correctly. That's quite a lot of current and quite a lot of power dissipation (>0.5W) in whatever component that outputs it (unless it's a switcher). I think you might be pulling down what is a power supply for the remote release rather than a signal line.

And without anything connected to the collector, of course you are going to get low voltage there. Still not sure why the reading jumped to 1.5V without grounding.

GerryR:
I think Magic hit it on the nose.  From the remote release units that I have looked at, they use a "stereo-type"  3-wire plug, which would imply plus, return and signal out.  Looks like you may be trying to switch the supply line to ground.  Just a guess without knowing the actual camera you are using.

yaun:

--- Quote from: magic on January 17, 2020, 08:18:15 am ---200 or 250 mA :wtf:

I'm not sure if you have figured out those particular cameras correctly. That's quite a lot of current and quite a lot of power dissipation (>0.5W) in whatever component that outputs it (unless it's a switcher). I think you might be pulling down what is a power supply for the remote release rather than a signal line.

And without anything connected to the collector, of course you are going to get low voltage there. Still not sure why the reading jumped to 1.5V without grounding.

--- End quote ---

I'm definitely expecting low voltage, but 1.5 seems crazy for the base current and transistor. I was expecting <20mv, which is closer to what I get when I change the grounding to the arduino.

'm super stumped.

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