Good day
I am working on a drawer cabinet that requires an led strip to light up inside the drawer once the drawer is opened. I want to use a 5 or 12v dc supply to charge a capacitor when the drawer is closed. Then when the drawer opens an led strip lights up and is powered from the capacitor. I drew the circuit I envisioned on falstad.com but it doesn't seem to work. The P transistor doesn't close fully once the switches are opened. Any help would be appreciated.

 

Have you calculated how much energy it would require to light the LED for x seconds?

 

Have you calculated how much energy it would require to light the LED for x seconds?

Not really. At the moment I am more concerned with the transistor not closing properly.

 

Won't articles inside the drawer block most of the light?

 

The circuit can not work because there is not enough base bias to saturate the transistors.
Instead, have the power feed make contact when the drawer is opened. No switches, no transistors, no batteries.

 

Not really. At the moment I am more concerned with the transistor not closing properly.

All you need is a switch, LED, resistor, and battery. No transistors needed.

 

Won't articles inside the drawer block most of the light?

Yes they would. But I plan on putting the switches in series with 3 drawers onto of each other. That way if I open the middle drawer the top 2 drawers' led's will light up. Then I actually put the leds on the bottom of the drawers and not inside.

 

The circuit can not work because there is not enough base bias to saturate the transistors.
Instead, have the power feed make contact when the drawer is opened. No switches, no transistors, no batteries.

How would I build such a switch? I want the drawer to be lit even if it isn't opened all the way.

 

How would I build such a switch? I want the drawer to be lit even if it isn't opened all the way.

I say switch but I really mean connected or disconnected from the power source

 

The circuit can not work because there is not enough base bias to saturate the transistors.
Instead, have the power feed make contact when the drawer is opened. No switches, no transistors, no batteries.

Is there any other way I could make the work? Perhaps logic gates?

 

How would I build such a switch? I want the drawer to be lit even if it isn't opened all the way.

I would use a micro switch that has SPDT contacts. Hence you use the contacts that close when the drawer is open.

 

I would use a micro switch that has SPDT contacts. Hence you use the contacts that close when the drawer is open.

So a switch that has a little roller that closes as soon as the drawer moves. It could work but it is still an extra switch. I will think about this option. Thanks

 

it is still an extra switch.

It isn't. Your schematic already shows a switch. Each drawer needs its own switch.

 

All it will take is one switch, mounted behind the drawer, to open when the drawer is fully closed. Not so very complex. In fact, one switch could enable all of the LEDs, if the system is not battery powered.

 

Reading between the lines a bit... I might be off-base here?

I think what you are saying is you want to have contacts at the back of the drawer charge a capacitor, which then illuminates the LED's for a short while when the drawer is opened and the circuit is broken?

First problem is that capacitors are really crappy at this application, a small rechargeable battery might be the answer.

 

Reading between the lines a bit... I might be off-base here?

I think what you are saying is you want to have contacts at the back of the drawer charge a capacitor, which then illuminates the LED's for a short while when the drawer is opened and the circuit is broken?

First problem is that capacitors are really crappy at this application, a small rechargeable battery might be the answer.

You understand correctly. I was hoping to avoid using rechargeable batteries since it would be more parts and larger space requirements. Would you still suggest batteries over capacitors even if I just wanted to light up the drawer for minute?

 

All it will take is one switch, mounted behind the drawer, to open when the drawer is fully closed. Not so very complex. In fact, one switch could enable all of the LEDs, if the system is not battery powered.

Yes that is what I was thinking as well. The problem is that I last worked with circuits on university 20 years ago.

 

How are you going to charge the capacitors?
It would be more efficient to power the LEDs directly from your power source.

 

How are you going to charge the capacitors?
It would be more efficient to power the LEDs directly from your power source.

I think the OP wants to avoid the moving wires?

 

The capacitor solution will be MUCH larger than a battery concept.
But... the capacitor idea would probably last for 10 years, batteries die in 3-5 years.