EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: xtreme_exploder on June 03, 2020, 09:56:32 pm
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I have a circuit that requires me to trigger a relay after a 12v signal had been present for a specified amount of time (about .4-.5 sec). I tried using a Airotronics THCU102S3E "delay on make" solid state timer relay wired between the signal box and the relay trigger terminal, but the function wasn't what i needed. It worked fine as long as there was enough time between signals, but would trigger if multiple signals shorter than the desired trigger time were present. I figured out that this was due to the reset time of the device, which is listed as 200ms during the timing cycle or 25ms after the timing cycle.
The desired function is this: the signal reaches the relay trigger only if it has continuously been on for the amount of time I want (.4-.5 sec), and stays triggered until the signal is off. If the signal turns off, even for an instant before the time interval I want, I want the time interval to reset and the relay not to come on until the next signal of the set time interval is present. I'm changing it so that a 5v/2mA signal triggers it instead of the 12v previously. I want it to function like the relay timer I tried, but with a much shorter reset time during the timing cycle. Does something like this exist? I tried searching for other delay on make relays but haven't come across anything that looks like it'll work. BTW, the 25ms reset time after the timing cycle is acceptable to me, but not the 200ms during the timing cycle. I know I could program a microcontroller to do this, but I want to make it as simple as possible and avoid that if i can.
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Look into Macromatic TE881 and TD8 programmable timing relays. Sometimes using two timing relays serially can provide additional functions.
Mike in California
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Only way I can think of without using a micro is to use discretes. Use an RC filter for the incoming signal and reset the capacitor using an FET to discharge it. Activate the relay when the rc level ~60%, using a comparator or zenor. Its mucky but will work.
It may be possible to do something with a 555 timer or retriggerable monostable.
Alternately, use a small uP. :-+
Best Regards
picclock