My Garage under attack from LEDs.
Failure #1, all's well that ends well.
Common sense says nothing lasts forever. I didn't expect the clock to fail quite this quickly. June 12, 2002 at 8:59PM the voltage regulator for the PIC failed. This supplied 8.5V to the 5V rail, which should never exceed 5.2V.
When I discovered the problem a little after midnight, the display was stuck at 8:59; the 7447 LED Driver chips were hot, the PIC chip was cracked from the heat it had generated, and the LCD display was completely filled with garbage. I wired in a 5 Volt regulated "Wall Wart" AC Adapter to supply the 5V the PIC needs. Amazingly, replacing the PIC chip with a new one brought the circuit back to life. All else was still functional, although I suspect the other components' life spans may be seriously compromised. Luckily, I didn't have to replace the LED driver chips, as I didn't have spare 7447 chips on hand, but will remedy that with my next order from Digikey.
With the summer thunderstorm season approaching, I decided it was now time to think about grounding for the circuit, so I ran a #12 wire from the PIC's metal alarm box to the metal of the garage wall, and connected it internally to the circuit ground. The garage's metal exterior is thoroughly grounded. This SHOULD give the circuit half a chance against damage, and at the very least provide a discharge path for static electricity.
Future plans are to build a monitoring and alarm system for the clock, such that the garage clock sends a reset signal to the monitoring circuit once a minute, and if the monitoring circuit fails to hear from the clock, it can alert me to the trouble. I'm thinking to use a fiber-optic link from the clock to the monitoring circuit here in the house, so lightning, ground loops, static and so on are not an issue. That will be another day when I have time to work on it. For now, the clock is back in service and was only down for about 4 hours.
Spring brings Green to the garage.
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