by pebe » Sat Jan 17, 2015 12:04 pm
This is a fairly simple way of doing it. The 555 timer is used as a level detector in this instance. Normally, the output goes high when Pin2 goes below 1/3 of the supply voltage, and goes low when Pin6 goes higher than 2/3 of the supply voltage.
Fitting the 3.3V zener diode to Pin 5 changes the level settings, so that the relay will switch on when the input goes above 3.3V and switches off when the input goes below 1.65V
I hope you find that useful. If you have any questions, please ask.
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