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

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!!!!!

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...

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

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.

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

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

Luciano, thats a great document. Any others that might be usefull?

The PIC worked on the breadboard today and when linked to the standard PCB it worked. However, when I placed the PIC in the same PCB and power supply the circuit stopped working. I have attached a PCB copy of the circuit

Any schematic?
Any Filtering problem?

Try sticking a large Cap across the power supply. To insure good filterization. Another thing... the MCLR pin...is it held high at one place and not the other? Or is it floating? If so, program it in the Define to stay high.

Dwayne