Is there a way to keep an Led on even when its power source goes off ?
I want to receive a 5v signal from an IR Sensor to light up the Led, have a circuit that keeps the led on until a reset button is pressed.
I have been trying with 2N2222 transistors but cant get what I want.
Any help appreciated.

 

No. They do not work without current flowing through them, except one special case I can imagine but never tried.

Use a short wavelength LED such as an ultraviolet or "very" blue LED. Paint it with glow-in-the-dark paint.

With luck the UV from the LED will make the luminescent paint glow, and the glow will continue after power is removed from the LED.

View attachment 352789
https://www.ebay.com/itm/313817145066?_skw=lluminous+paint&itmmeta=01K0C05D38RCFX5FZM529YR3J6&hash=item4910f59eea:g:8E4AAOSwRYBh0oIi&itmprp=enc:AQAKAAAA8FkggFvd1GGDu0w3yXCmi1dMihQUmUY3TTMqOXDL1FXKM1i96KAGA+bR7tu0LnJ2VdnO5bvtnBZ/A6KE9wF60YoMzdCFxc6gTmT3Uom5mHoT4+MZxpZRXuxTOvpIp6P/wAmKY9jG9cFpICq763LYmVaAGfp4m9goAVgM4mUYNE+09ZMoNHgUbHbeqr8vEVqOuyfizp3W5IdCxtmSNwOJvMpqFNWm1+gnHCOXfH03HZ9pemvmY4q3NvFhjA8nWS31qJLrcILXs+8bkRelNKZF2leqEXrqClrBp1JevZQ6+ddGA14dD8OV2j1qF86JM0th3Q==|tkp:BFBMutKVgINm

Is there a way to keep an Led on even when it`s power source goes off ?
I want to receive a 5v signal from an IR Sensor to light up the Led, have a circuit that keeps the led on until a reset button is pressed.
I have been trying with 2N2222 transistors but can`t get what I want.
Any help appreciated.

not sure why the text in the OP came out retarded.
Thanks for your reply Dick. it must somehow turn on a circuit that has a power source to feed the led.

 

Lookup "simple transistor latch".

 

...and while you are at it, please post your current circuit and we can go from there.

 

Latching LED circuit

Use a 3V button cell BT1 to keep the LED lit.
D1 is a red LED.

 

That`s perfect thanks MrChips.
also thanks to all replies.

 

Latching LED circuit

Use a 3V button cell BT1 to keep the LED lit.
D1 is a red LED.

View attachment 352804

Question ... isn't R1's value a bit too high? ... I would've used something like 270 ohms instead ... I'm just say'n

 

Question ... isn't R1's value a bit too high? ... I would've used something like 270 ohms instead ... I'm just say'n

R1 controls the LED brightness and hence the current drain.
High efficiency red LEDs can run on 1 mA even lower.

 

High efficiency red LEDs can run on 1 mA even lower.

It seems I'm behind the times ... I didn't know about high efficiency leds ... thanks for clarifying

 

How come the led is not on permanently if the 3v + is connected to it.
Do the transistors switch to provide the gnd for the led?

 

Do the transistors switch to provide the gnd for the led?

Yes, Q2 does that.

 

Thanks

 

If you still need touch reset, I will provide a solution later today.

 

When does the 5V signal from the IR sensor go low?
Is it just a momentary pulse?

Below is the LTspice sim of MrChips' (modified) circuit:

I added D2 and D3 so the return of the Set signal to zero from the IR sensor doesn't reset the circuit, and C2 so the circuit doesn't turn on from the parasitic transistor capacitances when power is applied.

If the V2 battery power will be continually applied, then C2 is not needed.

 

after 5 to 20 seconds.

 

Hi crutschow
Looks amazing but flies right over my head. I cant seem to get the simplest things to work.
The project i am building would require 20 separate signals that will each need this led solution, but hopefully only 1 reset button.
Ultimately i would like to have this made into a pcb with the smallest possible footprint.
I`d like to offer to pay to have a prototype made. please crutschow or anyone else who could get this sorted, please email me <snip>

Moderators note : removed email to avoid spam
Personal details can be exchainged in a conversation (pm)

 

If you need 20 separate signals with a single reset there is another solution using D-latches.

 

ok thanks to the mod. I`ll wait for a pm. cheers.
@ MrChips appreciate your ongoing messages.

 

CD4043 is quad Set-Reset flip-flop.
If you need help configuring this I can supply a circuit diagram.

https://www.digikey.com/en/products/detail/onsemi/MC14043BDR2G/3462302

10 pieces for £4.24
https://uk.farnell.com/on-semiconductor/mc14043bdg/4000-cmos-smd-4043-soic16-15v/dp/9665145

 

I bought some CD4013 chips and tried to follow a youtube video. if you could give me a simpleton drawing i`ll give it a go.
thanks.