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Shift Register Help

Former Member

Hi all,

I'm using 2 x 14 pin 74HC164Ns, cascaded together, to operate an LCD, 3 LEDs and a Piezo sounder. Controlled by a PIC16F874. Running at 4MHz.

My problem is: when I write to the shift registers, I get a clicking  sound on the Piezo, and flashing on the LEDs. The LCD is unaffected as  I'm driving the en input directly from the PIC.

The PCB has already been designed and manufactured, so I am a bit stuck.  Even toggling the clear input on the shift register doesn't solve the  problem.

Ideally I should have used a shift register with tri state outputs such  as the 595. However I am stuck with making what I have here work.

Possible solutions:

a) run the PIC at a higher speed?
b) fit a small filter to my LED and Piezo outputs (which are on flying leads) so they ignore these very short signals?

I'd appreciate your comments on the above - many thanks.

Phil

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  • 0 in reply to firatkocak

    Hello.

     

    At first you have to analyse if your problem comes from the harware or from the software.

     

    1. Re-solder the pic-pins (what are connected to LED, Piezo, ...) from PCB, or if you use a socket just pull them out of it and curve them in the air.

    2. Take a look with the oscilloscope at a. the pic-pins b. the solder points on the PCB

     

    After this measurement you know where you have to search for the fault!

     

    Please post the result of these test.

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