I was thinking that the Schmitt Trigger would do the inverting of my circuit from the OptoIsolator (absence of the current). Would this tie into the delay to the latching relay ? Could it provide the delay or does it have to be a separate 555 ?

Since the exact delay time is not critical you could just use a RC circuit at the input of the Schmitt Trigger to generate a delay, but you still need a 555 for the one-shot.

 

This application comes up often enough. There is an off-the-shelf solution, called an "impulse relay" but it is usually more expensive than the typical hobbyist is willing to budget for piddly projects ($30 or more, Vs. ~$1 for regular relay) but I feel obligated to mention it nonetheless. They are so expensive because they are uncommon, but I would think they would be more common considering how often the need arises. A while back someone (#12 or Shortbus, maybe? not sure) here on this forum said that they were going to make a "poor man's Impulse relay" circuit and publish it here on the site so we can refer people back to it when these threads come up. Not sure what happened with that...

 

This application comes up often enough. There is an off-the-shelf solution, called an "impulse relay" but it is usually more expensive than the typical hobbyist is willing to budget for piddly projects ($30 or more, Vs. ~$1 for regular relay) but I feel obligated to mention it nonetheless. They are so expensive because they are uncommon, but I would think they would be more common considering how often the need arises. A while back someone (#12 or Shortbus, maybe? not sure) here on this forum said that they were going to make a "poor man's Impulse relay" circuit and publish it here on the site so we can refer people back to it when these threads come up. Not sure what happened with that...

Thanks for suggestion but you are correct that $30 a pop is a bit over the top. In designing my railroad empire I may end up having over 20 block control circuits - that would blow my "mad money" budget ! I searched for the Poor man's Impulse relay - don't see anything like that. If you find it - please post the link.
thanks, Joe

 

Below is a modification that should work. The capacitor is charged through the resistor, which is then discharged through the coil to switch the first relay when the button is pushed. There isn't enough energy left in the capacitor to operate the alternate coil after the relay switches. And the current through the resistor is not enough to switch the relay after the capacitor discharges.

Note that the power to the second relay is derived directly from the 12V.

You may have to experiment with the value of the capacitor to get the correct value. Too small a value and it won't switch the relay. Too large and it will switch back.

Edit: I just noticed you don't want the relays powered all the time. In that case you can wire both from the capacitor, but you would need to double the size of the cap.

View attachment 55867

I have reproduced the circuit in post# 11 with the capacitor and resistor, 2 latching relays, all the wiring looks correct but when I push the switch nothing happens. If I energise the coil b of relay 1 the polarity changes over, as it does if I energise coil a of relay 1. If I close the switch after energising coil b the polarity changes but it will never go back after. Another thing i have noticed, if I apply 12v to the common of rl1 the relay vibrates but it always stops in the same position, the one where it will not change state, surely a random pulse should leave it in the other state sometimes? It seems like the circuit is biassed to one position of relay 1.
I add I am using 960Ohm relay coils and 4.5ms switching time so I am unsure of the cap/resistor value (using 20uf and 54k, it does work well in one direction)

 

I have reproduced the circuit in post# 11 with the capacitor and resistor, 2 latching relays, all the wiring looks correct but when I push the switch nothing happens. If I energise the coil b of relay 1 the polarity changes over, as it does if I energise coil a of relay 1. If I close the switch after energising coil b the polarity changes but it will never go back after. Another thing i have noticed, if I apply 12v to the common of rl1 the relay vibrates but it always stops in the same position, the one where it will not change state, surely a random pulse should leave it in the other state sometimes? It seems like the circuit is biassed to one position of relay 1.
I add I am using 960Ohm relay coils and 4.5ms switching time so I am unsure of the cap/resistor value (using 20uf and 54k, it does work well in one direction)

I saw this circuit and it looked much like what I had in mind so I tried it. The task I have to perform is to drive a slave clock which is expecting alternate polarity pulses once a minute, from a contact which closes at 30 seconds and opens on the minute, I have to use a relay with the coil energised by this contact for another perpose so I only have 1 throw available to give an output to the slave clock (using a dpdt relay)

 

You may want to consider putting the power source across the Common relay contacts and the load across the NC/NO contacts. If you use 2 relays and one activates in the wrong state as the other, the power source will short. Connected as suggested will just cause the load not to receive power. Which may be something you want. It would be much more desirable than shorting the power source.

 

Can someone please explain why this circuit will always work B to A but will never switch back A to B. When the switch is pressed the relay can be heard switching but it never stays in the other state, if I put 12v onto the coil it switches every time but never with the capacitor discharge. I have checked the coils both are 915 Ohm and switching times are quoted as the same for set and reset (4ms), the relays are HFD2 2 coil latching, 12Vdc

 

Can someone please explain why this circuit will always work B to A but will never switch back A to B. When the switch is pressed the relay can be heard switching but it never stays in the other state, if I put 12v onto the coil it switches every time but never with the capacitor discharge. I have checked the coils both are 915 Ohm and switching times are quoted as the same for set and reset (4ms), the relays are HFD2 2 coil latching, 12Vdc

What circuit?

 

The one that I referred to in my post #45, #46 and is shown in post #11 and #45 and here https://forum.allaboutcircuits.com/attachments/55867/
I think it may be due to the common contact making with both NO and NC for a short time when switching, i.e. make before break but why it works in one direction and not the other is strange, unless the set and reset contacts are different

 

The one that I referred to in my post #45, #46 and is shown in post #11 and #45 and here https://forum.allaboutcircuits.com/attachments/55867/
I think it may be due to the common contact making with both NO and NC for a short time when switching, i.e. make before break but why it works in one direction and not the other is strange, unless the set and reset contacts are different

 

Crutschow, I could do with some advice from you, this was your design, where have I gone wrong?

 

Crutschow, I could do with some advice from you, this was your design, where have I gone wrong?

Well, I just modified someone else's design and I've never built it.

Double check the wiring to be sure it's correct.

My simulation shows that the circuit is rather sensitive to the capacitor value.
In the sim it works properly only within a couple μF of about 24μF.
Don't see offhand how to make it less sensitive to that value.

A better circuit might be to use a D-flipflop controlling a single relay to get the desired toggle latch function.

 

Hi..,

Why not use a 4013 and couple of transistors to toggle the latching relay?
The 4013 would send a single pulse to the transistors to toggle the relay. The relay state would be persistent.

eT

 

Here's an option using a momentary DPDT Center-off toggle switch.
According to the diagram, each coil terminates on separate pins.

 

I think it may be due to the common contact making with both NO and NC for a short time when switching,

see my post #46. If you place the load on the Common set and the power on the NO NC set, there is no possibliity of a short to the power source. The way it is shown if one relay operates before the other, a momentary short occurs across the power supply.