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Help with troubleshooting simple transistor switch circuit

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yaun:


I have the simple circuit above. Q1 is a 2n3904.

The purpose is to actuate the shutter on a camera's remote shutter input. Assume that pin D11 is set to logic LOW.

The thing I'm curious about here is if I power the arduino via USB then I get ~30mv vce (multimeter attached to vce).

If I power the arduino with a power brick then I get 1.5v vce, and this seems very strange to me. Notably, some cameras throw an error if they are plugged in during this state.

If I am powering it with the brick and then ground the circuit to USB (connected to a hub) ground, then vce goes back down to 30mv or so.

I don't understand what is happening here, and I'm unsure of how to process what is happening here. I could use some help troubleshooting this or troubleshooting my assumption that this is erroneous behaviour.

Thank you!

GerryR:
I would like to know what the actual load is, but the first thing to do is to tie a 10k - 20k resistor from the base to ground.  The Arduino considers .8 V or less as ground (digital Lo).

Wimberleytech:
What is the "measured" (not assumed) state of D11 during both conditions?
Is the camera plugged in during this test?
What kind of load does the camera present to this input (your output)?

yaun:

--- Quote from: GerryR on January 16, 2020, 08:52:26 pm ---I would like to know what the actual load is, but the first thing to do is to tie a 10k - 20k resistor from the base to ground.  The Arduino considers .8 V or less as ground (digital Lo).

--- End quote ---

Base to ground resistor does not change the behaviour described. I tried a trimpot from 0-20k.


--- Quote from: Wimberleytech on January 16, 2020, 08:54:50 pm ---What is the "measured" (not assumed) state of D11 during both conditions?
Is the camera plugged in during this test?
What kind of load does the camera present to this input (your output)?

--- End quote ---


* Measured state of D11 is 2mv, 17µa according to my meter. (this does not change in any of the conditions)
* Camera is not plugged in.
* The only thing I can measure off the camera is 3.3v from tip to sleeve

Wimberleytech:

--- Quote from: yaun on January 16, 2020, 09:42:07 pm ---


* Measured state of D11 is 2mv, 17µa according to my meter. (this does not change in any of the conditions)
* Camera is not plugged in.
* The only thing I can measure off the camera is 3.3v from tip to sleeve
--- End quote ---

Tie a 10k resistor from the collector to 5V and run the test again.

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