circuit design help: momentary switch activates/cancels electronic switch

[matthewuw]

Here is the application:

I have a momentary switch. When I press it, I want to switch something
on (light bulb) and have it stay on even though momentary switch was
released. maybe 500 mA draw.

When I press it again, it turns the light bulb off. How do I do this?
This is in a 12VDC circuit.

Thanks!

 

[Ken Taylor]

Do you particularly want to use that switch or would you be prepared to swap
it for a push-on/push-off momentary action one?

Ken

 

[ehsjr]

Here is the application:

I have a momentary switch. When I press it, I want to switch something
on (light bulb) and have it stay on even though momentary switch was
released. maybe 500 mA draw.

When I press it again, it turns the light bulb off. How do I do this?
This is in a 12VDC circuit.

Thanks!

There are a number of ways to do this. Do you want
to learn, or are you just interested in having
a circuit that will do it?

Ed

 

[matthewuw]

Will in the end, I need a circuit to do this. But I do want to learn.
What I asked for is actually only part of the functionality, but I see
it as a building block to start with and was hoping I might figure the
rest out on my own.

 

[matthewuw]

Well a push-on push-off switch isn't really momentary. It feels like a
momentary switch, but doesn't function like one. I have to use a
momentary switch, no option because or existing hardware.

 

[matthewuw]

Well a push-on push-off switch isn't really momentary. It feels like a
momentary switch, but doesn't function like one. I have to use a
momentary switch, no option because of existing hardware.

 

[Terry Pinnell]

Here is the application:

I have a momentary switch. When I press it, I want to switch something
on (light bulb) and have it stay on even though momentary switch was
released. maybe 500 mA draw.

When I press it again, it turns the light bulb off. How do I do this?
This is in a 12VDC circuit.

Thanks!

This should do it.
http://www.terrypin.dial.pipex.com/Images/Momentary1.gif

There are many circuits for a 'toggle' or flip-flop, but that's the
simplest/cheapest I know of.

 

[Fred Bloggs]

This should do it.
http://www.terrypin.dial.pipex.com/Images/Momentary1.gif

There are many circuits for a 'toggle' or flip-flop, but that's the
simplest/cheapest I know of.

Did you simulate that?

 

[Ken Moffett]

Here is the application:

I have a momentary switch. When I press it, I want to switch something
on (light bulb) and have it stay on even though momentary switch was
released. maybe 500 mA draw.

When I press it again, it turns the light bulb off. How do I do this?
This is in a 12VDC circuit.

Thanks!

I've tried this and it works. Simple and cheap. Sub in a 12vdc supply and a
12v relay.

http://beradio.com/news/radio_pushonpushoff_switch_2/

 

[Fred Bloggs]

Here is the application:

I have a momentary switch. When I press it, I want to switch something
on (light bulb) and have it stay on even though momentary switch was
released. maybe 500 mA draw.

When I press it again, it turns the light bulb off. How do I do this?
This is in a 12VDC circuit.

You can use a miniature SCR bistable:
View in a fixed-width font such as Courier.

 

[Fred Bloggs]

Should be:
View in a fixed-width font such as Courier.

 

[Terry Pinnell]

Did you simulate that?

No, but maybe I'll have a crack at it when I get some time. Meanwhile,
I've put together this scan from my original source: "Elektor 302
Circuits", ~1985
http://www.terrypin.dial.pipex.com/Images/MomentaryScan1.jpg
which explains its working.

And I'm pretty sure I breadboarded it successfully a decade or two
ago.

 

[Jim Thompson]

Here is the application:

I have a momentary switch. When I press it, I want to switch something
on (light bulb) and have it stay on even though momentary switch was
released. maybe 500 mA draw.

When I press it again, it turns the light bulb off. How do I do this?
This is in a 12VDC circuit.

Thanks!

See "TogggleFlopAncient.pdf" on the S.E.D/Schematics page of my
website.

...Jim Thompson

 

[Fred Bloggs]

Here is the application:

I have a momentary switch. When I press it, I want to switch something
on (light bulb) and have it stay on even though momentary switch was
released. maybe 500 mA draw.

When I press it again, it turns the light bulb off. How do I do this?
This is in a 12VDC circuit.

Here is a less parts intensive version of the same thing, consumes about
50uA in the off state:
View in a fixed-width font such as Courier.

 

[Fred Bloggs]

No, but maybe I'll have a crack at it when I get some time. Meanwhile,
I've put together this scan from my original source: "Elektor 302
Circuits", ~1985
http://www.terrypin.dial.pipex.com/Images/MomentaryScan1.jpg
which explains its working.

And I'm pretty sure I breadboarded it successfully a decade or two
ago.

Thanks- I think I recall that article now, clever.

 

[Fred Bloggs]

See "TogggleFlopAncient.pdf" on the S.E.D/Schematics page of my
website.

...Jim Thompson

A little before my time, but those were the days...toggle on release.

 

[Ken Moffett]

I've tried this and it works. Simple and cheap. Sub in a 12vdc supply
and a 12v relay.

http://beradio.com/news/radio_pushonpushoff_switch_2/

I looked back at the circuit again and noted something they had left out.
The relay in their circuit was a 12vdc for the 24v supply. So for a 12v
supply you would choose a 5vdc or 6vdc DPDT relay. The resistance of R1,
R2, and relay's coil would all be approximately equal.

 

[matthewuw]

Okay, thanks for all the replies. Sorry to change things up on
you...but like I said early on, this is a learning experience for me.
It has occured to me that I don't want to worry about contact bounce
and that in reality, this will fit my application much better if there
are 2 momentary switches. pressing one of them turns the system on and
pressing the other turns the system off. i can probably adapt this
setup somehow from some of the provided circuits, so I will look into
it. this might actually simplify the circuit too i would think.
THANKS!

 

[Terry Pinnell]

Okay, thanks for all the replies. Sorry to change things up on
you...but like I said early on, this is a learning experience for me.
It has occured to me that I don't want to worry about contact bounce
and that in reality, this will fit my application much better if there
are 2 momentary switches. pressing one of them turns the system on and
pressing the other turns the system off. i can probably adapt this
setup somehow from some of the provided circuits, so I will look into
it. this might actually simplify the circuit too i would think.
THANKS!

How much simpler can you get than the circuits posted? Have you tried
any of them yet?

Hey, how about an even simpler approach: a single toggle switch? No
buttons, no electronics. AC or DC power supply in at one side, and out
of the other to whatever you want to control. Its explanation is as
follows: when you switch it one way, the circuit is powered on. When
you switch it the other way, the circuit is powered off again. Very
reliable, parts easily obtained. What's more, it has another advantage
over a button-based approach: the status of the circuit is always
visibly obvious (providing the two switch positions have been marked
accordingly, e.g. 'On' and 'Off' or whatever.) This advantage over
buttons applies even if the load has failed somehow (lamp filament
burned out, motor stalled, etc).

 

[Fred Bloggs]

Okay, thanks for all the replies. Sorry to change things up on

you...but like I said early on, this is a learning experience for me.
It has occured to me that I don't want to worry about contact bounce
and that in reality, this will fit my application much better if there
are 2 momentary switches. pressing one of them turns the system on and
pressing the other turns the system off. i can probably adapt this
setup somehow from some of the provided circuits, so I will look into
it. this might actually simplify the circuit too i would think.

View in a fixed-width font such as Courier.

..
..
.. 12VDC>---+-------+-----+-------+
.. | | | |
.. | | | 12VDC |
.. | | --RELAY---
.. | | |\ COM|
.. | - |/ |
.. | ^ |\ |
.. | 1N4001 |/ NO |
.. | | ----------
.. | | | |
.. o +-----+ +-----+
.. -| SWon | | |
.. o | | |
.. | | | |
.. +----[2.2K]---|-------+ |
.. | | |
.. [2.2K] | |
.. | | LAMP
.. | ||- |
.. +-------+--||< IRF510 |
.. | | ||- |
.. o === | |
.. -| SWoff 0.1U | |
.. o | | |
.. | | | |
.. +-------+-----+-------------+
.. ---
.. ///
..
..
..