16f628 Help Me And My Pupils!!!!!!!

[Mr. Wakefield]

3 pupils in my Year 11 GCSE electronic Products class have designed a snooker score board. We tested their projects on a breadbaord and they worked fine. As soon as we transfered them to the PCB they didnt.

The pupils have used 3 4026 7seg display drivers linked together. These circuits work well and count up to 999 as they should. When I link the PIC board to the clock on Pin 1 on IC 1 the number display does not stop it continues counting and there is no input. I have tied the clock down to 0 and tried holding the output to 0V through a resistor but there is no joy.

Can anybody advise? PLEASE!!!!!

[Melanie]

Posting a Circuit Diagram is a good start...

Are you telling us that even grounding the inputs to the 4026 they still count?

You've tried the obvious... like ensuring your PCB is a true copy of the breadboard? And you've sprinkled 100nF Capacitors liberally around the PCB's 5v rail (usually one at each chip) to decouple noise... And your PSU is rock steady...

[Mr. Wakefield]

I have managed to get the PIC board using the 16F627 to work. When the input goes high ouput 7 producess a number of pulses pending which input is used. This works successfully.

However, when I attach the fly lead to the clock on the 4026 it dies not count up when a button is pressed. I have added a pull down resistor and diode.

Furthur more. A poulse is seen to be recieved when a multi meter was placed on the pin. Very strange.

any suggestions

[sougata]

Dear Mr. Wakefield,

A look at the schematic with the associated code may help forum members to track down your problem. Otherwise only blind guesses.

[Mr. Wakefield]

I will post one up Monday when back at work. Thank you for your time.

[Luciano]

Hi,

Make sure the PIC and the 4026B use the same +5V and same GND.

See page 20 and 21 of this PDF.
http://www.rev-ed.co.uk/docs/PIC_electronics.pdf

Best regards,

Luciano