Momentary Latch Relay 0v Output
Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=31273
Printed Date: May 10, 2025 at 5:06 AM
Topic: Momentary Latch Relay 0v Output
Posted By: Hellraz0r1
Subject: Momentary Latch Relay 0v Output
Date Posted: April 29, 2004 at 12:41 PM
Ive been messing with alot of relay (spdt and single/double coil latches) and I cant get a good circuit. Id like to have a momentary ground pulse turn on a constant ground, then a second pulse turn it off. I know your going to point me to the latching setups and tell me to add yet another relay, the problem is Im making 3 switches, so thats 15+ relays!!! Thats just un acceptable, Can anyone point me to a good design or where I can find a single latching relay with a non dependent coil (IE you dont have to reverse voltage), I cant seem to find any. Thanks for any input. -Chad
Replies:
Posted By: xetmes
Date Posted: April 29, 2004 at 12:45 PM
you want to togle with a momentary switch? Its not really easy to do with just relays, if you want that many outputs you wil need a ton of relays.
Posted By: Hellraz0r1
Date Posted: April 29, 2004 at 12:48 PM
OK maybe u misunderstood me, Each switch is going to control 1 output, for a total of 3 different isolated circuits, making the relay cound 15+ Id Like to cut down on the number of relays. -Chad
Posted By: xetmes
Date Posted: April 29, 2004 at 12:58 PM
i think i understand, you want 3 switches that each have one output, the output state toggles with each press of the associated switch....?.. that would be a mess with 15 relays... You could use JK flip-flops tied as T flip flops, you will have to condition the input to remove the switch conact bounce though... you would also need driving transistors on the outputs to sink enough current for the relays...
Posted By: Hellraz0r1
Date Posted: April 29, 2004 at 1:18 PM
i had a circuit for a ic4027 but it never worked.... i got some latching relays but they have dpependent coils, im gettin screwed from every direction. I was hoping to get a latching circuit down to 3 relays but i doubt that is gonna happen. i only need the 0v output for some leds i have wired into my gauge cluster so Im thinking about using the 4 relay latch do drive my accessory with 12v and a transistor through a 5v regulator + resistor for my ground... thats still 12 relays tho...
Posted By: xetmes
Date Posted: April 29, 2004 at 5:04 PM
the JK should work, but there is a good amount of circuitry needed to filter the contact bounce. That many relays is kinda overkill. One way would be to use a microcontroller and just write some code for it... Since you are only driving LEDs the current draw is very little...
Posted By: Hellraz0r1
Date Posted: April 30, 2004 at 1:38 AM
this is a copy of the schematic i used: 
it did not work at all... Ive been looking for some info on turning this into a T-Flop but I just cannot find any...
Posted By: robbie2883
Date Posted: April 30, 2004 at 7:07 PM
When the button is pressed, the capacitor connected to the base of the conducting transistor will charge to a slightly higher voltage. When the button is released, the same capacitor will discharge back to the previous voltage causing the transistor to turn off. The rising voltage at the collector of the transistor that is turning off causes the opposite transistor to turn on and the circuit remains in a stable state until the next time the button is pressed and released. Note that in the LED circuit, the base current from the conducting transistor flows through the LED that should be off, causing it to illuminate dimly. The base current is around 1 mA and adding a 1K resistor in parallel with the LED will reduce the voltage to about 1 volt which should be low enough to ensure the LED turns completely off. 
------------- if its jammed force it - if it breaks in the process it needed to be fixed anyway
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