Fluctuating digital inputs

[pedja089]

That is just print scr, from my schematic.
My Vdd is 2.8V, so lower threshold is 0.56V. With 2K and 15K combination low level is 0.32V.
That is almost half of threshold, it works fine for me.

[Dave]

Bandaids,Bandaids,Bandaids, Just put an optoisolator and a couple of resistors on a small piece of Vectorboard and be done with it. If you are going to use the circuit in post #382 you might as well do it right with anh opto.

[pedja089]

If you referring to my post #14...
My circuit use only 10uA with all inputs shorted to GND.
Vdd for inputs is controlled by PIC. So just give me opto that uses less than 1uA and I'll be happy to use it.
By the way device passed ESD and RF immunity test without false triggering or any damage

[pedja089]

Double post. Bad internet connection...

[The Master]

Current usage isn't really a problem for me so I'm happy to use optos. They will be in a V2 of the PCB for next year though.

The existing PCB is running with a few minor modifications and debouce code and so far I've not had a single problem.

Thanks everyone for your help. This thread will be invaluable when I'm designing V2 and other similar PCBs. I'll also be paying more attention to noise from now on.

[Demon]

Good stuff. I'm in the planning stages on a residential alarm system and long runs of wire are a fact of life.

I'm using 4 strand telephone twisted pairs, don't remember if shielded. But I'll be sure to keep an eye on interference.

Robert

[Jerson]

I have a nagging doubt that you are seeing a R-M-W port problem. A schematic diagram will help clarify the scene for me.

[Dave]

Robert, An alarm system hey, When I worked for Westinghouse alarm company about 40 years ago we would use from 15 to 20 Ma. for our contact wetting current in loops. When using switches, you can't rely on anything less to break the oxidization of NO contacts. The system I designed for my home uses a cunstant current source for the NC loop as well as current source's the all NO switches inseries with the LED's powered by 12 volts. I have never had a problem with it. Using constant current allows for some loop resistance variation over time as switches and wiring connections age. No false alarms...... Also you DON'T have to worry about shielding the wiring due to electrical noise.