Making a latching relay with 555 timer

Cool and simple design. I’ve built a similar circuit before with a 555, but had timer function set by the value of a capacitor/resistor combination that powered a small relay. For a latching switch that uses a relay to power a heavier load using a low current type push switch, one could use two momentary push switches, one a normally open, one a normally closed. These two push switches would be in circuit in this manner: Press the N.O. switch and a + battery coil voltage flows through the push switch to a D.P.D.T relay coil and to the ground through the N.C. push switch , and it clamps. To make it latch you also feed + batt coil from the out side of N.O. push switch voltage to one of the two N.O. relay contacts, you then connect a wire between the other contact of the relay to the momentary N.O. Push switches “always hot side.” When you push the norm open (N.O.) switch, relay coil voltage flows and goes through the other N.C. push switch to batt negative & relay latches. Summery: When the relay clamps, the one contact of the relay hooked to + then resupplies the relay coil continuously. If one then presses the norm closed (N.C) switch, the relay looses its - Neg connection to the battery and the relay drops out, “opens up.” The other N.O. relay contact of the relay can then be used to switch the hot lead or + DC of another power source to whatever load or device you are wanting to power up. There are also other relays such as T.P.T.T. Triple pole triple throw and more. Except these relays with many poles then become expensive. The resting contact state of each contact can be purchased different, with some contacts being N.C (normally closed) in unpowered state as well. Your circuit can do the same and with only one switch if you hook your output that powers the LED instead to a relay coil. I’m not sure how much current a 555 timer chip can supply for a relay coil, I think 0.100A (100mA)? The relay coils operating voltage and resistance would need to be selected accordingly with LED & current limiting resistor removed to operate a relay directly instead. I suppose as an alternative, one could pop in a opto isolator in place of your LED, then power a relay coil through the opto isolator’s switch side “collector” hooked direct to the positive & then through the relay coil to - Neg source of the project if the 555 cannot provide enough voltage and/or current to power the chosen relay directly. Of course Opto-Isolator’s also have max voltage and current ratings for their switch side that one would need to observe. SCR’s are also fun to use for latching circuits. 😎👍

Great explanation, appreciate the thorough schematics.

Thank you, this is an amazing video with a good & clear explanation. Keep up the good work !

Nice work. Thank you for making and posting this video. Thank you for the schematic and explanation of function. 🙂

Sweet circuit. Thank you!!

Great explanation, and also a very useful circuit.

Really informative, thanks alot!

Nice video, thanks for sharing it with us, well done :)

Awesome effort sir. 🎉

Very well presented and explained, thank-you... I've subscribed.👍

Love it. You should make some more interesting videos on the LM505, as I see it everywhere in all sorts of different hacking videos but never understood what was so special about it!

Nice video. Very succinct!

Lovely work

Would it be possible to replace the push switch with a mosfet so that a switch to one of the power supply rails could be used ?

Wow worked for me after some serious tinkering 😅

This was exactly what I was looking for. Only in my project the momentary switch is connected to ground on one side, which I cannot change. I therefore tried to control a relay with my switch. This relay replaces your switch in the schematic. Unfortunately the logic is not stable anymore after replacing the switch with a relay? Any tips? I used the NO and C pole. Maybe the capacitor does not work with the relay?

Nice.

Great circuit i did it & it works perfectly,but sometimes when i turn the supply off & on again the circuit turns on by itself! How to illuminate that please?

I tried to use this circuit in practice to control a lamp from two separate switches that are 60ft apart. The circuit is so unstable it either turns on by itself or it refuses to latch and I look like an idiot trying to press the switch multiple times. I was advised to put a small cap between 5pin and ground and one in parallel to S1 to filter high frequencies. Did anyone try this and how did you fix it. Mine latches after the cap hack but not from the first try.

Where can i buy such readymade module and what is it called????