| Electronics > Beginners |
| Weird relay module driving |
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| ReWoP:
Hi all, first i would like to say that i'm a electronics hobbyist with no formal education on this subject so please bare with me :-BROKE :P I have those ebay 5V relay module with 3 pins - VCC, GND and IN - and to latch the relay i just need to pull IN pin to ground. But the circuit that i intend to use to control it has a little quirk. I need to monitor a voltage source (about 9V) and i would like to drive the relay in the following manner: 1- If the voltage source = 0V Then relay OFF 2- If the voltage source = 9V Then relay still OFF 3- If the voltage source drops from 9V to 0V Then relay ON The voltage source always starts at 0V, after 'x' amount of time it jumps to 9V, after 'y' amount of time it goes back down to 0V and after 'z' amount of time the whole "system" resets and repeats again. I could use a microcontroller to implement this (like an Arduino) but i think its an overkill... I'm in the impression that this could be done with some transistor logic and also, maybe, with some OP AMP, but i can't get my head into it.. Please help! :scared: Big thanks in advance! :-+ |
| soldar:
You want a falling edge (from 9 V to 0) to set a bistable? Then it stays set until when? It is never reset? |
| ReWoP:
--- Quote from: soldar on January 04, 2019, 11:19:37 pm ---You want a falling edge (from 9 V to 0) to set a bistable? Then it stays set until when? It is never reset? --- End quote --- Thanks for the reply! The state should change (turn the relay ON) when the 9V is disconnected (voltage source is again 0V) and the relay should stay ON until reset (circuit voltage off then on). |
| soldar:
That should be easy to do with an R-S flip-flop latch which can easily be built with a couple NAND gates. When the circuit powers up it is reset and when the 9 volts disappear it is set. What voltage is the main circuit? The 9 volt will always be present when the main circuit powers up? |
| ReWoP:
--- Quote from: soldar on January 04, 2019, 11:55:21 pm ---What voltage is the main circuit? The 9 volt will always be present when the main circuit powers up? --- End quote --- The main circuit is 20v but since the relay is 5V ill use a step down converter to get the 5V to this "monitor circuit" and relay operation. When the circuit powers up the voltage source (the monitored voltage) is 0v. |
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