I am sure there is a button that will fit my requirement, however I do not know the correct search term to find it.
I would like a button that when pressed only sends a brief "on" signal but then returns to "off" state even if the button is held down.
Any help is appreciated.

 

I don't know of any mechanical switches that would meet that quiteria but certainly can be accomplished with some additional electronics. What is the application?

 

A button won't do it. But... A button and a one-shot circuit will. 555 timer circuits are what you need to learn and will help you in the future. There are other ways...

one shot circuit schematic - Search (bing.com)

 

Many years ago when flying model rockets I used a scrapped switch out of a telephone system. If you pushed the button down part ways the contact would close. But if you pushed it down further it would open again. But the problem with that switch is that if you wanted a longer signal you had to hold the button with just the right pressure. THEN when releasing the button from being fully depressed you'd get another switch closure.

One trick I learned fairly recently was using a relay and a capacitor. When pushing the button the cap would begin to charge. The current pulled through the cap would drive the relay. Once the cap charged sufficiently the relay would drop out. Therefore you'd have a momentary switch, assuming you hold the button long enough.

 

This circuit below will do about what you seem to be after. You press the button. As soon as the current begins to flow it does so until the capacitor has charged enough so as to not draw anymore current through the coil. Once the cap has charged to a sufficient level the relay will drop back out. The diode will absorb any residual back EMF preventing the switch from experiencing a back current and aid in discharging the capacitor through the resistor. Depending on how you want the switch to behave you wire your controlled circuit to C and NO for a momentary closure or C and NC for a momentary open. For exact timing to whatever specifications you need you will have to choose the component values. The diode will prevent the cap from back feeding the coil, so the coil won't close a second time when you release the button. I'm assuming you want this to close then open in a very short period of time, say something like 1/10th of a second maybe. Component values don't need to be excessively high. The resistor should be high enough to direct sufficient current through the coil AND low enough to drain the cap fast enough for the next time you want to push the button. Again, I can only assume you may want to push the button once every five minutes or so. Maybe one minute. Too large a resistor will restrict how soon you can re-energize the circuit.

The other alternative is a 555 circuit as others have suggested. A "One Shot" or a "Monostable Non-Retriggerable" circuit. More components but more control as well.

 

Using a much larger capacitor and the modified relay output feeding back to the coil will begin the charging phase of the capacitor for a much longer duration. Even if you let go of the button prematurely the relay will continue to hold until the cap reaches a charge point where it no longer draws sufficient current to hold the relay. As I mentioned before, I used to fly model rockets. This circuit would have made a great launch controller. I could push the button and get a reliable output every time with sufficient duration to fully ignite the rocket motor. Replacing the push button with a timer circuit I could build a "Count Down" timer that will enable me to set the rocket then get out into the recovery field in time to recover the rocket. But now it seems as if I may be hijacking the thread. The point of this circuit is to show you there are options. THIS relay is a SPDT type. You can get them in SPST, DPDT, 4PDT and so on. If you don't understand the SPDT and other acronyms - just ask.

 

Since nobody has as yet welcomed you to AAC; "Welcome to AAC."

I am sure there is a button that will fit my requirement

Exactly what are your requirements? Knowing that will help us give you the best answer possible.

 

I am sure there is a button that will fit my requirement, however I do not know the correct search term to find it.
I would like a button that when pressed only sends a brief "on" signal but then returns to "off" state even if the button is held down.
Any help is appreciated.

The brief “on signal” is called a “pulse” and the pulse has a specific duration of time that it is “on”.

1. What the voltage levels coming from the button?
2. What is the required pulse voltage levels output when the button is pressed?
3. What is the required pulse duration?
4. What is the output pulse operating?

 

Hi,
Button and Switch Basics - SparkFun Learn
Good luck..........

 

A push button, resistor, and capacitor could do it.
We just need more details as to what is being triggered.

 

Since nobody has as yet welcomed you to AAC; "Welcome to AAC."

Exactly what are your requirements? Knowing that will help us give you the best answer possible.

I have a sound module that requires grounding a control pin to change tracks . If it receives a ground signal for more than a brief second, it starts the first track from the beginning instead of switching to track 2

 

In that case a capacitor and a couple of resistors should suffice.

 

A push button, resistor, and capacitor could do it.
We just need more details as to what is being triggered.

I have a sound module that requires grounding a control pin to change tracks . If it receives a ground signal for more than a brief second, it starts the first track from the beginning instead of switching to track 2

 

The brief “on signal” is called a “pulse” and the pulse has a specific duration of time that it is “on”.

1. What the voltage levels coming from the button?
2. What is the required pulse voltage levels output when the button is pressed?
3. What is the required pulse duration?
4. What is the output pulse operating?

I have a sound module that requires grounding a control pin to change tracks . If it receives a ground signal for more than a brief second, it starts the first track from the beginning instead of switching to track 2

 

Capacitor and 2 resistors. R1 may not be needed depending on input module.

 

View attachment 313178capacitor and 2 resistors.

Good approach. However, we don't know if the momentary ground signal is from something that is otherwise floating or is dependent upon a constant source to hold it from ground. Old 8 track tape decks had a solenoid that would trigger a cam that would move a head to the next track. However, holding a signal didn't force it to go back to the start of the first track.

So what we want to do is ground a signal briefly. This is why I think your circuit might be the right way to go. But at the same time you're providing a constant voltage via R1 which might not be useful or even possibly detrimental to some as yet unknown set of circuitstances. (made that word up!)

Until we know more - - - eh - - - kind of insufficient information. Possibly just a PB and a cap with a parallel resistor. Possibly forgetting VCC. But we just don't know for sure.

 

This is what I had in mind.



R2 might not be needed if the input circuit already has pullup.

 

I have a sound module that requires grounding a control pin to change tracks

Still waiting to find out exactly what Sound Module....

 

This circuit below will do about what you seem to be after. You press the button. As soon as the current begins to flow it does so until the capacitor has charged enough so as to not draw anymore current through the coil. Once the cap has charged to a sufficient level the relay will drop back out. The diode will absorb any residual back EMF preventing the switch from experiencing a back current and aid in discharging the capacitor through the resistor. Depending on how you want the switch to behave you wire your controlled circuit to C and NO for a momentary closure or C and NC for a momentary open. For exact timing to whatever specifications you need you will have to choose the component values. The diode will prevent the cap from back feeding the coil, so the coil won't close a second time when you release the button. I'm assuming you want this to close then open in a very short period of time, say something like 1/10th of a second maybe. Component values don't need to be excessively high. The resistor should be high enough to direct sufficient current through the coil AND low enough to drain the cap fast enough for the next time you want to push the button. Again, I can only assume you may want to push the button once every five minutes or so. Maybe one minute. Too large a resistor will restrict how soon you can re-energize the circuit.
View attachment 313171
The other alternative is a 555 circuit as others have suggested. A "One Shot" or a "Monostable Non-Retriggerable" circuit. More components but more control as well.

The diode is not required at all because the current in the coil never changes suddenly.The relay engages fairly fast when the button closes, but then the current drops rather slowly. As the capacitor approaches full charge the current drops. And if the button is released then the capacitor/relay circuit current drops less rapidly.

 

Was uncertain about the diode. So many times I've seen people add the diode when I didn't think one was needed.