Keypad activates relay

Posted on Dec 23, 2012

Moreover, the method does not entail programming and the concomitant, almost inevitable, debugging. A CD4016 CMOS analog switch, IC1, forms the heart of the system. Depressing the key labeled `1st` closes the topmost switch (between pins 1 and 2), which latches itself via the diode connected between pins 2 and 13. The same topology repeats three times, with the keys labeled `2nd,` `3rd,` and `4th.`

Each switch provides power to the next one, so that depressing the key labeled "3rd" before the "1st" or "2nd" key does not activate the third switch. The Disable keys, connected in parallel, disable the entire chain by short

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