On/Flash/Off LED

[Tommy_Ent]

Hi there.

I'm trying to build a circuit that creates three states for an LED (on/flash/off), and is controlled with a momentary switch... something similar to your typical bicycle light.

I need it to be small and cheap, and I only have room for one push button (otherwise I would just use a three position switch). Does anyone have any ideas of how to build this, or where to look? I'm stumped at the moment.

Thanks,
Tommy

 

[CocaCola]

Kris will likely come along with some fancy circuit, but until then...

Momentary switch with hardware debounce into a 4017s clock input... Output 1 of the 4017 toggles transistor that lights LED... Output 2 toggles a transistor that powers a 555 timer circuit, and thus flashes the LED... Output 3 is left floating, thus an 'off' state, note this is really not 'off' it's still drawing a little current as it waits for the next press... If this small drain in the 'off' position is a concern the circuit would need to be designed differently... And of course a few steering diodes on the LED so that output 1 & 2 don't cross...

 

[trondyne]

Why not use a three position switch that in pos 1 is OFF, in pos 2 is ON and in pos 3 runs a blinker?

 

[CocaCola]

Why not use a three position switch that in pos 1 is OFF, in pos 2 is ON and in pos 3 runs a blinker?

He/she hinted why right after they said they only have room for the push button

I'm assuming changing the switch is not an option in their design...

 

[trondyne]

He/she hinted why right after they said they only have room for the push button

I'm assuming changing the switch is not an option in their design...

Silly me... I guess that's the case, still a 3 pos toggle I would think would use a very small space. :/

 

[CocaCola]

Silly me... I guess that's the case, still a 3 pos toggle I would think would use a very small space. :/

I guess it all depends on the actual layout or desired function, a toggle still requires back and forth movement (and your ability to manipulate it) and this might not be suitable to the design...

 

[Tommy_Ent]

@CocaCola,

Thank you for the suggestion, but I need something that does not draw much power as the momentary switch can be the only means of turning the device off. I'm really curious how other products do this, because it seems very common... even a dollar-store flashlight I found has this capability, but I still can't replicate it.

I'm assuming that it's a dedicated IC, but where would I look for that sort of thing?

 

[Tommy_Ent]

As for the 3 position switch idea, it needs to be a button to fit with the design. I'm an artist and product designer first, and an electronics designer only as needed

 

[trondyne]

Actually me too..

I'm sure someone will post a circuit.. It's just a matter of applying some kind of sequential logic to the switching I'd guess..

I'd be interested in seeing the flashlight in question--and the specs are unknown. What's inside?

Jim

 

[CocaCola]

@CocaCola,

Thank you for the suggestion, but I need something that does not draw much power as the momentary switch can be the only means of turning the device off. I'm really curious how other products do this, because it seems very common... even a dollar-store flashlight I found has this capability, but I still can't replicate it.

You can replicate it real easy with a micro (like almost all commercial stuff uses) as newer micros go into deep sleep that for all practical purposes draw less current when they are sleeping then the batteries self drain just sitting there not hooked up to anything... There are also a few 'fancy' zero drain momentary on/off circuits out there but since you want additional logic on the same button, they are unusable... Or better stated not real practical in the end...

To do this with a micro you, well need to be setup to do programming and burning of microchips and you also need to make sure your choice of chips offers extreme low current deep sleep modes...