Delayed temporary signal

[mf7480]

Good morning

I’m new here so excuse the very basic layman’s terms, but the crux of what I’m looking for is a device to enable a one second signal after a one second delay of a proximity sensor activating, and again a one second signal after a one second delay from when the same proximity sensor deactivates.

I have 24 of these units in total to do, but they must all work independently, although if one controller could do the lot wiring to a central point wouldn’t be a problem. It’s a 12v system.

Looking to make this work as simply and cost effectively as possible.

Many thanks in advance for your help, if your need any more clarification please do ask.

Best regards

MF7480

[jmelson]

I’m new here so excuse the very basic layman’s terms, but the crux of what I’m looking for is a device to enable a one second signal after a one second delay of a proximity sensor activating, and again a one second signal after a one second delay from when the same proximity sensor deactivates.

You could use an XOR gate and an RC delay to create a pulse on both state changes of the sensor, and then a one-shot to generate your one second delay, and another one shot to generate
the one second pulse width.  The CD4070 XOR gate can run off of 12 V directly.  The 4538 dual one-shot can also run off 12 V.  Make sure to get the real CD4xxx series, not the 74C4xxx
which are only good to 5 V. 

To make the edge detector, put the sensor signal directly into one input of the XOR.  Use a resistor in series to the other XOR input, and a small capacitor to ground at that input.  This causes a
delay on that input, and the gate responds with a positive pulse when the two inputs are different.  The choice of R and C values need to be chosen for the rise and fall times of the sensor output.

Look up the datasheet for the 4538, it's more than I want to explain here.

Jon