simple circuit with miniature press switch

[Musisoft]

Hi,

Im looking to make a simple simple circuit.

3 AA batteries + 1 LED and a miniature switch.

But I need a miniature push switch to put the LED on with 1 press and another press to put it off. It's not a mechanical switch. Its the same switch that you can find on your VCR or DVD player front body.

I only need the circuit for the switch. I want to do it without IC if possible

thx

 

[monkeytree]

from an old school project i can remember that all it takes is one transistor and two resistors but i can not remember howthey go together

 

[Nigel Goodwin]

from an old school project i can remember that all it takes is one transistor and two resistors but i can not remember howthey go together

I don't see how it could be done with only those components?.

 

[jrz126]

Maybe monkeytree is thinking of a simple logic inverter?

The simplest solution would be to use an on/off type switch instead of the momentary one that you have now.
Other than that, you'll need a latch or flipflop or something like that.

 

[jbeng]

A Google search of "transistor flip-flop" turned up this circuit, which uses two transistors and a handful of other components. The text describes it's operation in pretty good detail. If you just want one LED, you should be able to just leave one of them out of the circuit, but don't remove it's resistor.
Here's the link for the page it came from:**broken link removed**

**edit** After looking at this circuit more closely, its actually a free-running oscillator which will "flip-flop" the LEDS back and forth as long as the pushbutton switch is held down. It could be modified to do what you want though. Sorry bout that!
JB

 

[Musisoft]

I know i can make it simpler with on/off switch but im sure someone knows the trick to do it with a momentary switch.

I dont want 2 led flashing one after the other. Just 1 led stay on if I press the switch and goes off if I press it again.

Maybe its impossible too...i dont know

 

[FRIED]

**broken link removed**

 

[Nigel Goodwin]

After looking at this circuit more closely, its actually a free-running oscillator which will "flip-flop" the LEDS back and forth as long as the pushbutton switch is held down. It could be modified to do what you want though.

Yes, it's an 'astable multivibrator', to latch you need a 'bistable multivibrator'.

 

[eblc1388]

I know i can make it simpler with on/off switch but im sure someone knows the trick to do it with a momentary switch.

I dont want 2 led flashing one after the other. Just 1 led stay on if I press the switch and goes off if I press it again.

It is anything but simple. Most people cannot wire up what you wanted with a simple momentary switch and an unlimited number of normal(not-latching) relays.

Maybe its impossible too...i dont know

Not impossible but difficult enough for most people but I guess someone will immediately post a circuit less than 3 minutes after I said that.

 

[Musisoft]

Im gonna try this
thx FRIED for the link


thank you all

 

[Analog]

I would like to know what happened to FRIED's circuit and how Musisoft did with this. I PM'd them days ago, w/o a response. Does anyone have FRIED's circuit? As his link is now gone???

I have the same issue, and would like to find out if this or anyone else's ideas would work!

I think FRIED's link is to Diana Todd's old web page, which is now removed - or is FRIED really Diana?

 

[Dr.EM]

This does exactly what you want, I have used it on a few occasions. May be more complicated than you thought and it does use current when idle. Adapting it for your needs is pretty straightforward but ask for help if you need.

 

[Analog]

Dr. EM, thanks for the schematic. For my application, I guess I would need only one of the three units shown. Also, I need to switch a DC load of up to 75W @ 12VDC, therefore I'll need to put a MOSFET in there to do that. I guess I could just replace the bjt with an N-channel power device? Or would I need additional current boosting before the MOSFET? Thanks.

 

[audioguru]

The CD4069 can drive a power Mosfet perfectly with a 12V supply, with the source of the Mosfet grounded and the load is between its drain and the 12V supply.

 

[Roff]

This does exactly what you want, I have used it on a few occasions. May be more complicated than you thought and it does use current when idle. Adapting it for your needs is pretty straightforward but ask for help if you need.

Doctor, I'm not seeing how it draws current when idle (if the LEDs are off).

 

[Dr.EM]

I assumed the 4069 inverters drew some quiescent current, mabye not? Either way it's very small compared to 75W.

 

[audioguru]

With any supply voltage within their ratings, if the outputs of all 6 inverters are high or low without a load, the supply current of a CD4069 is typically only 10 nano-amps. That is one-hundredth of one uA. If it didn't self-discharge, a little 9V battery could power one for more than 10,000 years.

 

[Dr.EM]

Right, I didn't know it was quite that small :0

 

[Analog]

excellent, great contributions folks.