Help needed with flip flop relay

Thread Starter

Billall

Joined Aug 14, 2021
4
Hello, I am new here, and have very limited circuit design abilities, so please be patient!! I am working on a project using a pre-designed flip flop relay board. The working power will be converted to 12vdc, and will be turned on by the application. I need to create a negative pulse each time the power comes on to switch the relay. I saw a circuit using a 555, but that was switching the positive side. If you were to ask the length of the pulse, I could only guess at .5 second. I don't presently have the board in hand, so I don't know if I can simply keep the ground applied until the power off. Any suggestions with a drawing would be most apricated!

s-l1600 (4).jpg
 

bertus

Joined Apr 5, 2008
21,667
Hello,

The large part on the right is an 78M05, wich is a 5 Volts 0.5 A regulator.
The voltage range of 6 to 24 Volts is to large, as the 78M05 will need at least 7 Volts for correct functionality.
78MXX_recommended operation conditions.png

Bertus
 

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Thread Starter

Billall

Joined Aug 14, 2021
4
Yes, as far as the voltage regulator is concerned, I think my 12v in should be fine. I see that the transistor suggested will give me a negative voltage from zero, but is it providing a momentary connection to my ground like in the illustration?
The second ic on the board is a Henery hr810. Couldn't find much info on it, but I'm wondering if it is similar to a 555? And would my addition of a 555 be redundant? Again, could I leave that trigger connected to ground for 1 cycle?O1CN01qEVCbg237lmi1Hilo_!!71027209.jpg
 

Juhahoo

Joined Jun 3, 2019
249
Not anymore clear to me, what are you actually after. Do you have push buttons?, what is the 555 for !?
What negative voltage ? What is this HR810 doing there ?
Full functionality description would create less questions.
 

Thread Starter

Billall

Joined Aug 14, 2021
4
Ok, I am using this flip flop relay to control 24vac for an irrigation application. I have one switched 24vac wire coming in. I plan to make a rectifier board to convert this to 12vdc for the working power. According to the illustration I provided, the relay switches back and forth when a ground circuit is completed to the trigger terminal. This has to happen when power is applied, as there will be no separate trigger button. When the power is shut off and reapplied the relay should be triggered again, giving me my second output.
Hope that makes more sense. I am unclear as to my best way to trigger this board with the available wiring.
 

ElectricSpidey

Joined Dec 2, 2017
1,962
Problem is each time the power is removed the relay may reset and you may only get one function available at each power up.

You will need to keep the power constant to the power inputs for what you want to work properly.
 

Thread Starter

Billall

Joined Aug 14, 2021
4
I had thought about that. I am not sure about that until I get it in my hands. It seemed to me the relay would stay in position until triggered again by that pulse trigger. If not, I would have to add a 9volt battery as a keep alive source.
 

ElectricSpidey

Joined Dec 2, 2017
1,962
"By default the relay is release"

The relay itself looks like a pretty standard cube type, so I wouldn't expect any memory for getting across power outages.
 

crutschow

Joined Mar 14, 2008
28,165
I need to create a negative pulse each time the power comes on to switch the relay
As noted, if the power is removed from the relay, it likely will be in an unknown state when the power is re-applied.

If you add a keep-alive battery, it would have to supply the relay coil current (likely in the neighborhood of 80mA) when the relay is in the energized position and power is removed.
A standard alkaline 9V transistor battery won't supply that current very long.

If you can power the HR810 circuit separately (which I assume is the latch) from the 9V backup (using diode isolation), then that would likely require much less keep-alive current.
The relay then would then be energized when the power is reapplied.

You may want to consider a latching type relay, which requires no power to stay in either state.
 

Juhahoo

Joined Jun 3, 2019
249
Ok, I am using this flip flop relay to control 24vac for an irrigation application. I have one switched 24vac wire coming in. I plan to make a rectifier board to convert this to 12vdc for the working power. According to the illustration I provided, the relay switches back and forth when a ground circuit is completed to the trigger terminal. This has to happen when power is applied, as there will be no separate trigger button. When the power is shut off and reapplied the relay should be triggered again, giving me my second output.
Hope that makes more sense. I am unclear as to my best way to trigger this board with the available wiring.
Draw a timing picture where you have input and output separated.
 
Last edited:

eetech00

Joined Jun 8, 2013
2,644
Hello, I am new here, and have very limited circuit design abilities, so please be patient!! I am working on a project using a pre-designed flip flop relay board. The working power will be converted to 12vdc, and will be turned on by the application. I need to create a negative pulse each time the power comes on to switch the relay. I saw a circuit using a 555, but that was switching the positive side. If you were to ask the length of the pulse, I could only guess at .5 second. I don't presently have the board in hand, so I don't know if I can simply keep the ground applied until the power off. Any suggestions with a drawing would be most apricated!

View attachment 245733
You can try something like this. This will need a DC supply of 9v to 24v.
R2/C2 provides a Trigger delay to allow the module to power up. R1/C1 controls how long the trigger is held at 0v.
With a supply of 24v, Trigger delay is about 350mS, trigger held is about 275mS (to reach 6v after the trigger delay). The times will be shorter with a 9v supply.

We'll need to know the trigger input threshold voltage at the supply voltage you intend to use.
You'll need to experiment with the R1/C1 and R2/C2 values.
1629077194062.png
 
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