Toucam SC1 mod interference

[12dstring]

I'm modding somebody's toucam pro II for them, and have just finished all the electronics - but there's a problem.

It's totally fine in normal exposure mode, but when switched to long exposure the screen changes to pixelated horizontal bands flickering on the screen, and the webcam emits a sort of high pitched squeel. There's the odd occasion when it will work, then when you start taking long exposures the first will be fine, but then on the 2nd, 3rd..etc frame it'll be covered in the lines again.

My hunch is it's some kind of interference problem, but I'm using screened cable to connect to the parallel port, and it happens even if the parallel plug isn't plugged in. One thing to mention is that sometimes if holding it, it'll be fine.. but then when you let go...

It's driving me mad and obviously because it's someone else's webcam, and I'm meant to be returning it withing a few days... all nice and working... I'm worrying about it a lot

Any advice would be greatly appreciated,

[George]

Maybe a earthing problem if its OK if your holding it as it will ground thru you. I'd double check all your connections and maybe add a ferrite ring or 2 to the signal cables.

[Naz]

Maybe a earthing problem if its OK if your holding it as it will ground thru you. I'd double check all your connections and maybe add a ferrite ring or 2 to the signal cables.

Second that Sounds like an earth or poor connection. Recheck all your soldering, make sure you haven't got a dry joint.

naz

[12dstring]

Thanks for the replies.

The usb cable already has a ferrite ring, I added one to the parallel cable but doesn't seem to have had an effect.

Been round everything probing for continuity, and it all seems ok, everything's connected to everything else it's meant to be.

Here's a piccy....

by an earthing problem, do you mean something isn't earthed that should be?

[Naz]

Possibly, or maybe a screening problem. Looks as though something is causing an interfering signal, and causing the effect. Maybe a small ferrite bead fitted to the ends of the leads at the circuit board end, as close to the board as possible. Sorry, but it sounds as though, trial and error to eliminate the problem.

I had a similiar problem with a power amp that I built years ago, took ages to find the problem, and that ended up being an earth loop, causing the amp to oscillate. Cured that with ferrite beads on the output transistors legs, and one on the preamp input.

naz

[12dstring]

Found the problem!

(I'm an idiot)

When drawing out my schematic, I managed to swap over two wires to the switch. When in normal exposure mode it was fine, as the two wires were connected normally, but when in LX mode the wrong wire was being connected to the +5V rail.

Thanks for getting me to look deeper for my problem anyway!