Re: Problem with PIC & LCD display


"Steve H" <steveu@xxxxxxxxxxxxxxxx> schreef in bericht
news:DiqSa4ATM0GIFwpI@xxxxxxxxxxxxxxxxxxx
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


Reading your descriptions I'm almost sure the problem is in the power grid,
most likely the ground side. You may find some clues by removing the ground
and power wires between processor board and display and replace them by
(relatively) thick, short wires directly from the regulator on the processor
board to the display. You may add some (as short as possible) wires from the
regulator to the processor as well.

petrus bitbyter


.

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