I have problem. if open a fan near counter .it reset to Zero

tsupuntu · Joined: 05 May 2006 Posts: 9

I create counter show on seven segment. I use switching supply 12Volt then pass 7805 regulater for pic CPU (16f628a).
I have problem. if open a fan near counter .it reset to Zero or some time hang.
Why is this problem..? Please help me.

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

You probably do not have a large enough capacitor in your power supply circuit or maybe missing decoupling capacitors. There are other possible causes but without seeing a schematic there is not much more I can add.
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tsupuntu · Joined: 05 May 2006 Posts: 9

thank a lot

I use Capaciter 470uF for input "IC7805" and use 470uf for output
input =12 volt

Ttelmah · Guest

What _smaller_ capacitors do you also have present?...
The problem is that electrolytic capacitors, do not work well for higher frequencies. This is why typical capacitors on supplies will have a 470uF, in parallel with a 0.1uF ceramic capacitor. You would think that the latter would effectively do nothing, but it is essential to block HF signals which the electrolytic has little effect on. Also, it is vital to have a small capacitor close to the PIC itself, and similar capacitors close to anything else switching at high speeds.

Best Wishes

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

It could be a floating pin (unconnected). The most likely suspect is
the MCLR pin. It should have a pull-up resistor to Vdd on it.
You might also have a missing ground connection on some chip (Vss pin).

If you think the problem is caused by temperature, then get a can of
freeze spray and test every chip in your board. Freeze the chip, and
also the surrounding components and see if the board fails.
This thread has a link to a photo of the freeze spray.
http://www.ccsinfo.com/forum/viewtopic.php?t=27442