GLCD and TouchScreen trouble

[SteveB]

I am trying to get a GLCD and a TouchScreen working together. I’ve got them both working separately just fine. But, when I put them together, the GLCD goes blank expect for a thick line at the top (like the “liquid” is pooling at the top of the screen).

I haven’t had a lot of time to fiddle with it, but if the TS is held above the GLCD, there isn’t any problem. Even just propping one edge on a pencil, between the black GLCD bezel and the TS keeps the problem from occurring. But as soon at they “mate”, the screen misbehaves. There is a slight “attraction” between the items as they come together. It takes a Reset or powerdown to fix the problem, just removing the TS does not restore the GLCD


Anyone work on this stuff before and have any ideas. I'd sure like to avoid a time consuming troubleshooting session if possible.
SteveB

[skimask]

Have you tried isolating them completely, like with a piece of tape or something only around the edges of the LCD frame?
Sounds like a grounding/static problem to me...

[SteveB]

Yea, that's my next step, after I get back tonight.

[SteveB]

Here are some more details.

If I place a piece of plastic, or rest it on some rubber bands, or both, I get this:


Now, if I place the TS on a couple of ordinary pencils, it works fine:


Also, if the TS is only about 1/4 of the way on the GLCD, it seems to be OK as well:


Any Ideas whats causing this? I will be playing with it to see if I can get a minimum clearance, but I like to know whats going on.

SteveB

[skimask]

Here are some more details.

Any Ideas whats causing this? I will be playing with it to see if I can get a minimum clearance, but I like to know whats going on.

SteveB

Capacitive touchscreen type thing? Or resistive?
If it's capacitive, maybe it (or the LCD) isn't not grounded well enough and inducing a charge back into the LCD. Or maybe you have to TOTALLY isolate the two...who knows. Looks pretty goofy to me. Ya gotta wonder how all those PDA's handle it.

[SteveB]

Using some various piece of thin plasic, I can get no closer than 1/4". If I reduce the gap by 1/32", it blanks out.

Capacitive touchscreen type thing? Or resistive?

It's 4-wire resistive.