Robbing LEDs from flashlights

There's a soldering gun in my possession.

 

Yes it has 3AAAs

 

@theblindchicken i was thinking maybe it's possible to slap the whole circuit board inside the dome light. Just don't know if I could wire it for power correctly or not. Mounting would be a secondary concern.

 

Probably when I find the answer I'll think it was a stupid question

 

Dang, just go buy it is such an unsatisfying answer to what IMHO is a great question. It's like saying just go to the dealer and buy whatever over price options he's tacked onto the truck. Real men know how to turn a wrench and run a soldering iron.

OP here's a schematic for a 6 LED array. If you have to buy the resistors you'll be into this project maybe $1 and that's if you over pay.


if you want to try different approaches here's a link http://led.linear1.org/led.wiz

 

You need to power that with a constant 4.5 to 5 volts. truck voltage will overload it pretty quickly.

 

The three separate LEDs are wired in parallel. All 24 LEDs are wired parallel according to that pcb layout.

 

come tinker with this 2wd to 4wd conversion

 

Now THAT would be fun

 

Where in the Lexus was it? Doesn't seem very bright. Are you using that in the cab?

 

... Predicting the future....
2nd gen Tacoma Market Place
WTB.... OEM overhead done light...

 

Ohm my where is thread going?

 

Two things that come to mind,

You can run a DC/DC converter. Should be able to get it to around the 3-5v required by the circuit. Only problem would be ensuring that the converter would be small enough to fit along with the led array. With this you'd be setting the voltage for the circuit.

May be able to run a load resistor in series between the +12v and the array. With this method, you'd be setting the amperage in the circuit and the load resistor would step down the voltage. Issue with this route may be that you create too many amps into the array and burn up the leds. Also, would require calculating the necessary amperage of the array.

Feel free to correct me if i got myself twisted around.

 

This might feel like rocket science, but it's not. In my schematic the 3 LED's in series plus the 120 ohm resistor will drop the voltage down to the 3.3 volts needed to light the LED. You could go with more LEDs and a smaller resistor or fewer LEDs and a bigger resistor and in the end you'll get to the same place. And, after looking closely at the back of the flashlight you have a couple of 120 ohm resistors down at the bottom (marked with a 120). Now, soldering surface mount devices isn't easy, but if you can reuse those parts the cost of the project is close to zero.

 

Completely overthought the problem..... Also would've helped if I noticed that the PCB was posted.

@Bennoclarke, @jsi's solution is just about as easy as it gets.

 

That's actually (3) 12ohm resistors in parallel for the 24 LED's. two 10ohm resistors for the 3 LEDs. I assume they went that route for current handling.

Only way to confirm actual ohm is with an ohmmeter.

 

Oops you're right. duh

 

Seems like the OP is encountering a lot of resistance. I wonder what could be done to rectify the situation.

OP have you consulted with ELI the ICE man yet? His reluctance to chime in might signify his lack of capacitance to handle a situation like this.

 

OP - I finally saw your PM. I'm putting my answer to the question here for those that might want to follow in your foot steps. IMO this is a great first electronics project, about the worst thing you could do is burn your finger on the soldering iron. Even if you soldered things wrong you might let the smoke out of an LED, but you've got a bunch of them so the impact is minimal.

So before the plans here is the obligatory warning. Please be careful, designing and building with electronics can be habit forming, and this poses a real risk to your pocket book. I swear it's a sickness every bit as addictive as modding your truck. (what? you were expecting me to tell you this can be dangerous? naw, just don't be stupid and you'll be fine.)

I'll leave to you to google how to de-solder parts, there are bunches of youtubes out there that do a far better job than I ever could. Get yourself two 120 to 180 Ohm 1/4 watt resistors. You don't have to be too precise on the resistors, close enough is good enough. If you have a choice I'd go with the 180's because voltages can be up to 14 volts. Get perf-board or some other thing to mount your project on. Sorry I can't be more help than this, but I've never even removed my lights so it depends on what's there already and how much you are willing/want to mod the light.

Here's perfboard:



And here's your schematic.

Once you've desoldered the LED there will be a flat side you can feel with your fingers. That's the negative or cathode side. Connect them together, cathode (-) to anode (+) like I've shown and that's all there is to it. (resistors don't care which way you connect them) I'd test each line of LED's using what ever 12 volt source you have, battery's, battery charger, or truck battery. That way if you do happen to let the smoke out it won't stink up your truck. If you want to do 9, 12, or more LEDs just keep adding or subtracting rows of LED's and resistor as you see fit. Once you're satisfied that it's working insulated the leads and make the connections inside the cab.

I know that's not a complete step by step, but the big parts are covered and I've left you plenty of room to call the project all yours.

Cheers!

 

Freakin sweet! Thanks, man. Looks like fun and what you've given me makes it look pretty simple.

Glad to see my silly post didn't die, after all.