Single Fire Toggle Switch

[k2x5]

Hi,

I'm working on a circuit, and run into a snag. Here's what I want to do:
- User Flips Toggle Switch to On position (Locks there)
- Single pulse makes it to destination

The obvious problem I'm running into is that flipping the toggle to on creates a continuous connection. The only way I can think of to prevent this is by using a latching relay which breaks the connection when the coil is energized (When the toggle goes to on) Which I very crudely illustrated in the attached JPG.

Does anyone know of an easier method of doing this?

Thanks in advance for any help.

 

[KMoffett]

How long a pulse? What's supposed to happen when the toggle switch is opened?...a second pulse?...nothing?

Ken

 

[k2x5]

A fraction of a second would be fine.

The actual intended application is to use it on a keyboard in place of the keys. (Long story)

Opening the toggle switch will result in a reverse pulse (Though that may need to come from a second source) which is why I was hoping there was another solution.

 

[mbarazeen]

from your title i understand that you need the relay to latch continuously when the switch is pressed & released. see the attached diagram, hope it will full fill your requirement. you should have another reset push button or have to disconnect power to the relay to reset it.

 

[KMoffett]

Opening the toggle switch will result in a reverse pulse

So closing the switch...the first pulse is 0V>+5V>0V
Opening the switch...the second pulse is 0V>-5V>0V?
or
Opening the switch...the second pulse is +5V>0V>+5V?
Ken

 

[mbarazeen]

Opening the toggle switch will result in a reverse pulse (Though that may need to come from a second source) which is why I was hoping there was another solution.

if i understand you correctly, you mean the circuit you posted will have a reverse pulse? normally you have to use a free wheeling diode across the relay coils for DC.

 

[k2x5]

from your title i understand that you need the relay to latch continuously when the switch is pressed & released. see the attached diagram, hope it will full fill your requirement. you should have another reset push button or have to disconnect power to the relay to reset it.

Sorry, thats just my bad explanation. I'm actually looking for nearly the exact opposite.

I'd like it to allow a single pulse to pass (Given my original diagram, I was assuming that the amount of time it took to energize the relay's coil would suffice to connect the circuit from Source -> Destination) and then for the latching relay to break the circuit.

The reason I need it to do this, is I want to replace a key on a keyboard, so I need a single pulse (Akin to pressing a key) and then nothing. If the circuit remains connected it will continually send the pressed key to the computer.

So closing the switch...the first pulse is 0V>+5V>0V
Opening the switch...the second pulse is 0V>-5V>0V?
or
Opening the switch...the second pulse is +5V>0V>+5V?
Ken

That I'm not entirely sure about yet. It is my understanding that in order to get a Latching relay to "un-latch" you need to reverse the polarity on the coils?

 

[k2x5]

if i understand you correctly, you mean the circuit you posted will have a reverse pulse? normally you have to use a free wheeling diode across the relay coils for DC.

Sorry no, the reverse pulse isn't yet a part of the circuit I posted. I haven't gotten as far as un-latching the relay yet.

 

[KMoffett]

The attached is a relay pulse generator. The length of the +5V output pulse depends on the value of C1, the relay's coil resistance, and the relay's drop-out voltage. You get a brief pulse out when SW1 closes, and nothing when it opens. If we had a schematic of your keyboard, it could probably be done with an IC.

Ken

 

[OlPhart]

I vote to both save yourself a Lot of interesting grief And get familiar with one of the basic blocks in electronics: a 555. It's non-retriggerable, so switch bounce isn't an issue and can be Easily set for whatever pulse width you want. Max supply of 18 Vdc is high enough for most demands.

When I was on the low rungs of the learning ladder, I ate them like CornFlakes. I do things differently now, but a 555 will Always have its' applications.
Please, Enjoy the vast flexibility of a truly Fun chip... <<<)))