I'm having difficulty figuring out a (hopefully) simple timer circuit using probably 2 x 555s or a 556 and I hope someone can advise.

Here's my objective - I will have a 12V trigger, sent positive for several hours at a time by the relay of a daylight sensor. When first triggered, I want to provide a momentary output of say, 1 second, to energise the latch coil of a latching relay. The pulse only needs to be short, irrespective of how long the trigger duration is. That part is easy enough, I can use a one shot monostable oscillator 555 timer circuit.

But when the trigger is switched off, I want to output another momentary, 1 second pulse to a second coil to un-latch the relay. That's the part I can't figure out.

Other info..................
There is a permanent 12V supply available and also a 24V supply.
The latching relay is actually 24V, so if the 555/556 circuit can switch it directly it would be a massive bonus. Otherwise, I'll just put a pair of 12V relays in the middle to isolate the two voltages.
The reason for having a 24V latching relay is that there will be a long cable run, also with a manual latch/un-latch override 3 way switch at the other end. Using 12V isn't going to be bomb proof enough.
If the circuit is going to switch 24V directly, I need to protect it from any problems caused by the manual overide ptting 24V at opuput 1 or output 2.
The 12V trigger could just as easily .be 24V if you'd prefer
It doesn't matter if one of the outputs is a negative voltage and the other positive, because as above I can isolate from the latching relay if necessary.

So in summary:
12V and 24V supplies. 12V trigger, several hours duration. Output 1 is a one second pulse on trigger positive. Output 2 is a one second pulse when trigger drops to zero again. Outputs 1 and 2 are for opposite coils of a latching relay.

The attached diagram explains the timing I'm trying to acheive.

Many thanks

 

I'm having difficulty figuring out a (hopefully) simple timer circuit using probably 2 x 555s or a 556 and I hope someone can advise.

Here's my objective - I will have a 12V trigger, sent positive for several hours at a time by the relay of a daylight sensor. When first triggered, I want to provide a momentary output of say, 1 second, to energise the latch coil of a latching relay. The pulse only needs to be short, irrespective of how long the trigger duration is. That part is easy enough, I can use a one shot monostable oscillator 555 timer circuit.

But when the trigger is switched off, I want to output another momentary, 1 second pulse to a second coil to un-latch the relay. That's the part I can't figure out.

Other info..................
There is a permanent 12V supply available and also a 24V supply.
The latching relay is actually 24V, so if the 555/556 circuit can switch it directly it would be a massive bonus. Otherwise, I'll just put a pair of 12V relays in the middle to isolate the two voltages.
The reason for having a 24V latching relay is that there will be a long cable run, also with a manual latch/un-latch overide 3 way switch, using 12V isn't going to be bomb proof enough.
The 12V trigger could just as easily .be 24V if you'd prefer
It doesn't matter if one of the outputs is a negative voltage and the other positive, because as above I can isolate from the latching relay if necessary.

So in summary:
12V and 24V supplies. 12V trigger, several hours duration. Output 1 is a one second pulse on trigger positive. Output 2 is a one second pulse when trigger drops to zero again. Outputs 1 and 2 are for opposite coils of a latching relay.

The attached diagram explains the timing I'm trying to acheive.

Many thanks

View attachment 263019

Configure a dual edge detector to trigger the 555.
You can make one with CD4093B gates.

What is the part number of the latch relay?

 

Sorry, should have said:
If the circuit is going to energise 24V coils directly, I need to protect it from any problems caused by the manual override putting 24V back upstream at Ouput 1 or Output.2.
This could be at any random time, either when latched or un-latched. Even if a manual switch latches or unlatches the relay, I still want our timer to send the momentary pulses at the start and end of the trigger period.
I'm assuming a couple of 1N4001 diodes would do the trick for isolation, but would welcome some guidance.

Apologies for the fat fingers and the afterthought.

 

hi OD,
This basic 555 circuit will give a pulse when the Vsup is switched Off.
E

 

Relay is from RS - 176-2920 . Hongfa HFD3/012-L1 . I can post the data sheet if allowed. It has separate latch and un-latch coils, not a single reversible coil, hence the need for two separate outputs from the timer.

Also, There will likely be several relays as part of a lighting array being latched and un-latched by this timer, all of them the same spec ,up to 8 in total. Hence the reason for the remote overrides and the need to be iso;ate from any momentary voltage coming back up from the override switch(es).

I'm grateful for the quick feedback. My problem isn't so much in figuring out the circuit in principle as in getting to the detail of componets and layouts. So I'd be grateful if you'd point me at a circuit diagram rather than a more generic "use X and Y".
Cheers.

 

So in summary:
12V and 24V supplies. 12V trigger, several hours duration. Output 1 is a one second pulse on trigger positive. Output 2 is a one second pulse when trigger drops to zero again. Outputs 1 and 2 are for opposite coils of a latching relay.

You can invert the trigger pulse with a transistor and AC couple that to the trigger of the first 555 based one shot. For the second one shot, you just need to AC couple the trigger pulse to the OS trigger.

 

Cheers Eric.

 

Cheers Eric.

Note that that circuit will give an output pulse of approximately 0.1s. You wanted 1s.

The timing resistor values I gave need to be tweaked to get 1s to account for capacitor tolerance.

Since the relay coils are 24V, you'll need to add transistors to the timer outputs.

 

Thanks Dennis. The attachment goes to an Error 404. Could you re-post a link please?

 

Thanks Dennis. The attachment goes to an Error 404. Could you re-post a link please?

Must be a site problem.
https://forum.allaboutcircuits.com/...ce-please.185687/#lg=attachment263033&slide=0

 

Here's a circuit using two 555's or one 556:
Since the 555 triggers on a negative going input, I added transistor Q1 to invert the signal for the trigger rising edge.
The transistor can be just about any small NPN BJT.

The outputs can drive a transistor to generate the 24V latch signal.

At the bottom is a circuit using one CD4093 IC package, if that works better for you.
The circuit does generate an Out2 pulse at power up.
If that's a problem, I can add some circuitry to prevent that.

 

Guilty as charged, I gave the 12V part number (chosen for a different job but it was on my RS basket list) from the same relay family, in error. To all intents and purposes it's the same though, except for the voltage.

I'm super grateful for all four solutions which came so speedily in reply to my question. An hour with some Vero board and a soldering iron this weekend ought to get me there or thereabouts.

The other part might take a bit longer longer. The sunrise/sunset controller providing the trigger signal will be Arduino based with a real time clock and a 365 day sun position calculator. Fortunately the 1000+ lines of code is open source from t'interweb and the only changes I need to make are for local latutude and longditude. Wish me luck!

 

hi OD,
Post your project development as you go, sounds interesting.
E
OT: A location 7 miles due East.

 

Transistors Q1,Q2 needed only for 24v relay. If using 12v relay, 555 output can connect directly to C3.
Edit: Added base resistors

 

This is probably the simplest you can do it. The devices are MOSFET gate drivers with Schmitt trigger inputs such as MCP1402. You can probably find a dual gate driver, but the only one I can think of at the moment lacks the Schmitt trigger
Set the RC time constant to the pulse width you need.

 

This is probably the simplest you can do it.

He has a two coil relay which requires two signals.

 

He has a two coil relay which requires two signals.

The part numbers ending in L1 are single coil (but I note that later he says he gave the wrong part number, but he doesn't say what the right part number was)