Probably a ground problem, but how to fix?

Other Hardware General Electronics
1

Hi all,

I have a 8mm film scanner I have described elsewhere, and now I wanted to build and 3D print a single power source for it. In the past, having separate power, it worked fine, but with three power sources it looked a mess.

I need 3.3V for the camera, 4.5 V for the lamp, and Arduino can have the 14V as such. So, I created the scheme of the image attached. The Arduino has two servos to run, and two switched to listen to.

So,

But something still sucks: as soon as I connect everything and plug in the Arduino too, it gets power from somewhere and the camera stops working. Arduino cannot be switched off at all.

I thought it was a problem with the common ground, so I attached a wire from the power ground to Arduino's ground pin, but it didn't solve the issue.

SO, wearing my flame-retardant underwear and welding mask, I submit to the flame war and ask for assistance in this, which must be elementary indeed, but with my limited experience I can't solve this on my own.

ground problem.jpg
ground problem.jpg1280×720 182 KB

2

Firstly you have created a ground loop with that extra ground wire - never a good idea if you are handling
analog signals. No loops please.

Secondly something must be missing from the diagram as the Arduino seems only to be connected to power.

Or is it perhaps that the Arduino (+ shield) is pulling too much current?

3

The Arduino is pinned to two servos and two switches, but in th eimage they're not in because it doesn't work even with the pins off. Actually I was wondering about the ground wire, but reading the answers here led me to think it was necessary.

The power from the wall is 9V / 1500mA, so you think it might be pulling too much and failing because of that? I'll find a bigger adapter then. Actually the camera too takes a fair share.

But in principle, if I lose the ground wire, it should work?

4

The ground wire is already present in the supply jack to the Arduino, your extra wire is just creating
a ground loop. A loop is a magnetic antenna, generally best avoided.

5

Thanks MarkT, you helped me along.

6

I thought it was a problem with the common ground, so I attached a wire from the power ground to Arduino's ground pin, but it didn't solve the issue.

No you always need a common ground, a ground loop will not stop something from working. There might be excess noise but it will still work.

The problem is one of parasitic powering. Some output is feeding into an input on and unpowered device and that is leaching power into that device through the protection diode inside the chip and powering it up.

7

The arduino switch in the gnd will do nothing as you have a ground connection in place from the source which is in parallel with it.

Why are you switching the gnd's? Common them all up and switch the positives

This is from trying to decipher the rats nest in the picture. You would be better off posting a schematic

8

Yes, I'll sort it all out, now that I have more info on how.

Many thanks :slight_smile:

9

MarkDerbyshire:
The arduino switch in the gnd will do nothing as you have a ground connection in place from the source which is in parallel with it.

Why are you switching the gnd's? Common them all up and switch the positives

This is from trying to decipher the rats nest in the picture. You would be better off posting a schematic

For Sure +1