A small (12508) app to lengthen a low-pulse 'bit'

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Submitted by: Holger Apfel
Download Link: link src6.zip

Those IR-detecting burglar alarms are fine for ex. atomatic lights (talking about low-voltage for solar apps here) but for 2 small nuisances:

1. They switch off quite fast ( say 10 sec.).
2. Repeated cycles put a lot of wear on the bulbs ( changed 15 bulbs out of 4 (!) in a summer).

So I programmed a small app which detects a low-pule at the input & pulls the same line low afterwards for a longer period of time. On-time may be easily verified by a clock output. After switching the whole thing off again i included a small 'blackout' to prevent the circuit from accidentally switching on again by bouncing lines.

Connect gpio 0 to gate of pull-down mosfet ( via 100 ohms). Connect gpio 4 to line in (via 10 k) = drain of Mosfet; source connected to Vss. Connect gpio 5 to RC-clock ( use poti to adjust on-time) gpio 1 acts like an output for a 1/32764 th of on-time.

Lamps to be connected between V+ and drain ( of circuit & IR-detectors in parallel)

Function:
1) IR det. senses person & pulls line low ( = turns light on)
2) circuit det. line low & pulls line low, too
3) somewhere in between, IR det. releases line but line stays low due to circuit
4) after on-time, circuit releases line, too & stays 'blind' a little while.
5) if line low atfer blind spot = 2), else wait till 1)

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