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I am trying to connect a normally closed gate sensor to a cheap 433 MHz remote so I can monitor the status of the gate at the front of our property remotely.

The remote has a normally open button that I plan to solder onto and connect to my sensor.

When the gate is shut the sensors circuit is closed. When the gate opens the sensors circuit opens until the gate is shut again.

The behaviour I am trying to achieve is... when the gate is opened, the remote button circuit should be closed for a short burst (about a second) to simulate the remote button being pressed, then released, regardless of whether the gate is left open or shut.

Once the gate closes and opens again, the behaviour repeats.

Any ideas how I could approach this problem?

I have done some research and found different methods of converting NC to NO behaviour and latching to momentary but I can't work out how to do both together!

Thanks in advance!

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  • \$\begingroup\$ Could you sketch some flowchart of what you really need? \$\endgroup\$
    – vtolentino
    Mar 8, 2020 at 8:34

1 Answer 1

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I think the word latching is a bit misleaing in your case, because what apparently you are trying to achieve is to add some delay when the gate is open. If that is the case, this can be done by using a RC timer as follows (This circuit uses FETs but could also be implemented with BJTs).

How it works:

The gate supply voltage (V3) emulates the behaviour of the gate. The sensor and the MYSW emulates your sensor, which in this case is depedent on the gate bus (V_gate<10mV -> gate and sensor are closed , V_gate>=10mV -> gate and sensor are open).

Whenever the gate is closed, the RC timer is quickly charged via M1 and D1. Once the gate is open, the timer begins to discharge at a rate given by approx. R2 ~ C1 until the FET M2 is turned off and the M3 is turned on. The diode D1 prevents the RC timer from discharging through M1.

I have also include two outputs (NO and NC) and the waveforms can be seen right below it.

Circuit

Waveform

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