Circuit Design to Convert Relay to Pulse(s)

[Goresin]

Hi, I hope someone on this forum can help me.

I need to convert a relay signal to push button pulse(s). When the relay closes, a single pulse (of about half a second duration, same as pressing a button) is required. When the relay opens, two pulses are required (same as pressing a button twice). Is there a low cost off-the-shelf solution to this? Can someone design a simple circuit to do this?

Thanks very much
Alex

 

[MikeMl]

Welcome.

When you say "relay signal" do you mean that you have an available isolated Normally-Open relay contact that is not connected to anything else?

Does the relay have Form C (NO-Common-NC) contacts available?

Does the added circuit have to use isolated switching contacts (like another relay), or could it use a transistor wired across the existing pushbutton?

If so, what is the open circuit voltage across the pushbutton when it is not pressed? Is one side of the pushbutton grounded?

In any case, the added circuit will have to be powered. What supply voltage do you have available?

This exact question has come up before. You might want to search previous posts...

If I was doing this project, I would use **broken link removed**

 

[alec_t]

Welcome to ETO!
Do you want the pulse to be positive-going (ground referenced), or something else?
What amplitude?
What load will the pulse have to drive?
What interval between the two pulses?

 

[ci139]

what about relative timing
does your 2-ry pulses need to occur (1)before , (2)exactly when or (3)any time after the relay opens/closes

 

[Goresin]

Thank you MikeMI, alec_t and ci139. I appreciate you taking the time to respond to my question.

To answer you all, I have searched the internet for a solution but not come up with anything simple and cost effective. If there is a previous post on this forum, please direct em to it and I apologize for re-posting.

MikeMI
Yes, you are correct, i is a simple NO-C-NC relay (two in parallel actually). With the pushbutton, I have not measured the voltage as I was more concerned with having the correct pulses, with which I could use an optical relay to drive. I will measure the voltage today and get back to you. In terms of supply voltage, again I will measure today and see what is available from the unit, otherwise I am happy to use a separate power pack of 5, 9, or 12 Volt.

alec_t
I'm not sure of the timings, really wanto to simulate pressing a button two times (it clicks), so the signal would depend on what it is driving to achieve the 'pulses' and as mentioned above I will measure the Voltage and get back here (and to see if an optical relay is required).

ci139
Timing is not critical in this case, delays of several seconds are completely acceptable.

Thanks again,
Alex

 

[Goresin]

Hi again. I have now measured the voltage across the pushbutton and it is 5.1V. I should have mentioned that this pushbutton is part of a circuit board. The board seems to have a supply voltage of 11.5V, which I could hopefully tap into rather than having a separate power source.

Alex

 

[AnalogKid]

This sounds familiar. Have your posted this question on other fora?

ak

 

[alec_t]

Is this for a car door locking system?

 

[MikeMl]

Here is a hack. You can see why I recommended using an Arduino mini. Maybe someone can come up with a circuit with fewer parts.

I am using both the NC and NO contacts on the existing relay at the input. V(in) shows when the relay is energized. Both the rising and falling edge of the relay signal create two of the pulses on the gate of the NFET V(g). The falling edge from the relay also triggers V(t) the 555 [see V(out)] which is used as a delay to make the third pulse at V(g).

I am using an NFET to "push" the button V(pushbutton) without adding yet another relay. I am assuming that you can make two connections by tacking wires to the two terminals on the pushbutton. You told me that one end is at 5V when the button is not pushed, and goes to 0V while the button is pressed. I am assuming that the other wire from the pushbutton is at 0V. I also assume that you are stealing the 11.5V from the device as shown.

 

[alec_t]

Here's my offering, using two ICs. As Mike indicates, using a MCU would be simpler if you have programming capabilities.

This assumes a stabilised 9V supply derived from the 11.5V. Supply decoupling components for the ICa aren't shown.

 

[ci139]

(ignore this message) the simple or the optimal solution depends on what the OP can do (about need to preserve the original circuit) and can do (about programming mc-s , designing/modifying a PCB) also the reliability of the mod
a good point to start with this custom mod - is that - the relay does not switch the wall voltages ?? nor is this the part of a production line (in case of a failure -- the financial damage ...)

the part that set me to a "lower course"

the signal would depend on what it is driving to achieve the 'pulses' and

?? it must be variable in what range

 

[ci139]

i must replace my relay model (works fine on simple circuits but in this one the simulation actually ended in simulation engine error)
anyways yet another concept for this

tough the µPU would likely be a better choice here
i still donno hows the relay that has to be modded latches either by a sys. generated signal / user button press /other and which part of the original circuit is available to read that relay its coil voltage current or output voltage current . . .
right now is just a random setup

 

[schmitt trigger]

Alec;
what is the Ux symbol in your schematic?

 

[alec_t]

It's the Dview device, used to display a bunch of digital waveforms one above the other in simulations. You can get a similar result by using Plot-Settings/Add-Plot-Planes in LTspice.

Here's an example:

Note that a side effect is that the vertical scale is compressed.

 

[Goresin]

Hi again. Apologies for late reply however I've been away with work. Reading through your comments it seems to get very complicated. Way beyond my abilities. I think therefore the most achievable and economical way is to go down the path of the micro-PLC route, as per MikeMI's suggestion. I had a look on eBay and they are surprisingly cheap.

To answer your question alec_t, this is for a sun intensity sensor switching a pool pump controller.

Thanks again for all your comments and suggestions.

Alex

 

[ci139]

the path of the micro

it likely is most energy efficient
/as with

seems to get

it is always the question trading in between the robustness , costs (misc.) , accuracy , reliability , operating range (noisiness , supply , system temperature)
** it does seem to get complicated coz to add a minimal protection against trivial "might happen" ""range events""
takes - ** seemingly - a lot of components

it is quite possible (realistic) to tune your setup with minimum no. of elements and even shared function (e.g. integrating all voltage dividers into a single ...) ones
so that the end result is operable in reasonably wide range of conditions

here's another variant - not power nor component count optimized - but uses similar setup 555 timers

-- i do not recommend this design but it shows how it (circuit with such function) can be optimized : here by replacing the Q1,Q̅1̅ with the Zero-Cross detector and defining/setting the delay for the fifth 555 we can ban the CD4049 and the 1-st , 2-nd and fourth 555 reaching more close to the design in ... post #9 . . . it takes a lot of playing around with any particular design to start getting it's particular anatomy correct -- and then with a chance of luck you may be able to come up with an "ultra compact" design -- try other www forums - someone might know your answer