Re: Problem with PIC & LCD display

In message <defe2008-c6fc-4bae-ae3f-cd12f938a52d@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, David L. Jones <altzone@xxxxxxxxx> writes

Can you post a photo of your board and setup? That often helps.
Do you have an oscilloscope?

Dave.


First of all, thanks to all who have contributed with help and suggestions so far. Much appreciated.

I've uploaded four pictures of the board etc. to:

http://www.spho.demon.co.uk/mux/

The unit isn't in a 100% assembled state, but you should see the general idea.

I've done some further testing today which has revealed the following observations:

Firstly, changing the 47uf capacitors on the input and output of the 5v reg to 4u7 tantalums, and also adding one to the decoupling of the PIC itself, made no difference.

Significantly perhaps, powering it with a 12v battery made no difference to the symptom of the display blanking when the 0v rail is touched with a meter probe/screwdriver. This eliminates a problem with the mains filtering.

As I've explained in previous posts, the LCD is written to twice a second normally. Slowing this down significantly to refresh every 3 seconds showed that the display does not blank immediately when the 0v line is touched but will blank on the next write operation. The probe or whatever only needs to be touched on the 0v potential momentarily. The display will stay on and (intermittently) blank on the next write.

Scoping the data and control lines to the LCD shows the signals are of the correct amplitude. All lines read zero ohms between LCD and PIC pins.

I'm going to replace the LCD module with an alternative type to see if it's that causing the problem.

--
Steve H
.

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