Hi guys,

I am writing here after exhausting almost 1.5 days of search for Off-On buttons that are latching. Basically the pushbutton should work like this,

Original state - OFF
When pressed once - switches ON and stays ON
When pressed again - OFF

Can someone suggest buttons like these? They have to be very small in size and should act as On/Off switches for dongle type of electronics. I am looking something like this



Thanks,
Kowshik

 

Google "alternate action pushbutton switch tactile" without quotes.

 

They have to be very small in size

Define "Very Small in Size".

 

Yesterday I asked you to define "Very Small in Size". Today I want to ask "How much current will this switch need to handle, and at what voltage?"

 

@Tonyr1084 To define Very Small in Size - I am looking something like tactile buttons as I've shown in the picture, dimensionally something of size 6(W) x 6(L) x 1.2(H) mm.

> How much current will this switch need to handle, and at what voltage?"
There are not much current constraints, something in the range of 50mA to 100mA is also fine. The reason being I'll use this switch to turn the base of a transistor or MOSFET On and off so all the heavy lifting of conducting the high current happens through the Source and drain pins.

 

Thank you for the answer. Have you thought of using a Flip Flop? (FF such as a CMOS D type FF). Is space a premium? If you DO go with a FF you'll need to debounce the switch as well. A small cap should do. But all this depends on how much space you have to work with.

 

Thank you for the answer. Have you thought of using a Flip Flop? (FF such as a CMOS D type FF). Is space a premium? If you DO go with a FF you'll need to debounce the switch as well. A small cap should do. But all this depends on how much space you have to work with.

I don't have too much restriction on space.

Can you please provide any circuit references regarding this Flip flop circuit please? I haven't implemented any such circuit.

 

Here's an AAC Textbook on the subject.
https://www.allaboutcircuits.com/technical-articles/circuit-and-operation-of-a-d-flip-flop/
Basically you set /Q (called "Not-Q" which is opposite of Q) as a feedback to D (Data). When the clock pulse goes high the FF sets Q to whatever state D is at the time of the clock rise. If /Q is high then D is high. When the clock pulse occurs Q goes to match D. As Q goes high /Q goes low. At the next clock pulse, since D is low then Q will go low and /Q will go high. This repeats for as many clock pulses there are.

Substitute the clock pulse with a switch and every time you close the switch the FF will change state.

Give me five min's and I'll bang out a drawing.

 

Below is the LTspice sim of an example PB (S1) operated bistable P-MOSFET switch that requires just one added control N-MOSFET:

You didn't answer Tony's question about what is the voltage you are switching?

 

At the clock pulse Q will take on whatever level is present at D. /Q will put out the opposite of Q.
At the clock pulse if D is High then Q will go high. Shortly after that, very shortly, /Q will go opposite of Q.

At this moment /Q is Low. So is D.
At the next clock pulse since D is Low, Q goes Low. This changes /Q to High.
At the next clock pulse since D is High, Q goes High. This changes /Q to Low.
At the next clock pulse since D is Low again, Q goes Low. This changes /Q to High.
At the next clock pulse since D is High again, Q goes High. This changes /Q to Low.

This goes on every time there's a clock pulse. As mentioned before, using a switch for the clock pulse will switch the output of Q from ON to OFF to ON to OFF. Every time you push the button it switches state.

This is not a complete drawing, just a basic operation of the FF. The switch may need to be debounced. And the output of Q may not be strong enough to drive whatever you're driving. A transistor or MOSFET will be needed to handle the heavy load.

 

I have a pile of Leviton Push On Push Off buttons rated for 1 Amp 250 volts, 3 Amp 125 volts and they work fine for low current DC. Leviton makes them as well as Gardener Bender. They come with 6 inch AWG18 leads. If you are in the US I will mail you one on me. Tis the season.

Ron

 

Am I missing something ?
Push-on push-off button switches are plentiful ??

 

Am I missing something ?
Push-on push-off button switches are plentiful ??

I thought so and the few I mentioned run about $6.00 USD off the shelf. I can't see where this should be complicated.

Ron

 

AliExpress and ebay are not the only or best places to buy components. Besides the big distributors like Digikey, Mouser, RS and other major suppliers, here's a summary of suppliers I've found reliable..

 

The thing that makes a pushbutton switch alternate-action is a mechanical mechanism. The smaller the switch, the harder it is to have a *reliable* alternate-action. This is why there are so many electronic methods of turning a simple momentary switch into an alternate-action function.

ak

 

The thing that makes a pushbutton switch alternate-action is a mechanical mechanism. The smaller the switch, the harder it is to have a *reliable* alternate-action.

Also, a momentary PB switch generally takes less force to operate than an alternate-action.

 

This is the typical form factor of a PCB mount latching pushbutton. They are always cubes, to accommodate the mechanism. This is the smallest I could find on AliExpress. They have various names, including push-on-push-off but Chinese manufactures seem to have settled on “self-locking”.

​

 

. If you are in the US I will mail you one on me. Tis the season.

Ron

hi Ron, So generous of you, unfortunately I'm based out of UK. But that's fine I'm thinking of implementing a power latch circuit as shown in this video as I already have a tactile user button that I'm using. So with some tweaks to software and some additional hardware I think I can implement this easily and keep my design easy.

 

You may want to use Ya'akov's suggestion in post #17.

Good Luck
Ron

 

But that's fine I'm thinking of implementing a power latch circuit as shown in this video as I already have a tactile user button that I'm using. So with some tweaks to software and some additional hardware I think I can implement this easily and keep my design easy.

You might want to check these:
https://na.industrial.panasonic.com...eup/light-touch-tactile-switches/series/79217



There are many tactile switches available as Mouser.
https://www.mouser.com/c/electromec...s/?contact form=SPST&switch function=ON - OFF