Advice on my IR LED flashlight project

Hi guys! First time poster. I'm looking for advice on creating an IR flashlight out of a cheapo LED flashlight. I'm trying to make my own homebrew TrackIR system on the cheapest of cheap.

I picked up a 5pack of cheap LED flashlights from Menards, $5.99 with a $5.00 rebate. Takedown was easy enough but now I need to find some IR LEDs to replace the 9 inside with, and that's where my lack of electronics experience shows. The thing's powered by 3 AAA batteries in a cradle putting them into series, this nets me 3.8 volts coming out. I tested each LED's leads while in operation and each of the 9 read 3.4v, hooked up in parallel it seems.

I have a soldering gun but now I need to know what IR LEDs to buy and insert, and whether I'll need to adjust the voltage. I don't even know what size these are, looks about... 5mm? I took pictures, with AAA battery for scale. Any advice would be helpful.

You might try some of the common electronics mail-order houses... Digi-key, Mouser, Jameco, and others.

For instance, Digi-key has a variety of 5mm IR LEDs, such as this...
http://www.digikey.com/product-detail/en/LTE-5208A/160-1061-ND/153250

The forward voltage is 1.2v, so you might need to wire two or three in series to get the same Vf as the white LEDs in there now. This would take a bit of hacking of the circuit board.

What's a TrackIR system?

Steve K said:

You might try some of the common electronics mail-order houses... Digi-key, Mouser, Jameco, and others.

For instance, Digi-key has a variety of 5mm IR LEDs, such as this...
http://www.digikey.com/product-detail/en/LTE-5208A/160-1061-ND/153250

The forward voltage is 1.2v, so you might need to wire two or three in series to get the same Vf as the white LEDs in there now. This would take a bit of hacking of the circuit board.

What's a TrackIR system?

Click to expand...

TrackIR is a system which uses a modified webcam and to track the motion of your head (or something attached to your head) for the sake of head-control in simulators like flight and combat sims. I disassembled a webcam, removed the IR filter, fashioned an IR pass filter out of a set of 3D glasses and now I just need an IR flashlight and some reflectors on my head to make it complete.

I was told it would be fairly easy to simply soldier out/in some IR LEDS into an LED flashlight to make an IR flashlight. The voltages worry me since I know very little about electronics. I can remove one or more of the three batteries to alter the voltage if that would help?

Since they appear to be in parallel, you're going to need resistors for each LED if you want to hook this up without hacking at your circuit board. 3.8V (you sure?) for 3.4Vf. Those LEDs are typically 20mA so figuring that you'll need a 22 Ohm resistor for each LED. That's assuming 3.8V from your battery pack. I'd assume 3.6V nominal, so really you'd want a 12 Ohm resistor for each LED.

LEDPunisher said:

Since they appear to be in parallel, you're going to need resistors for each LED if you want to hook this up without hacking at your circuit board. 3.8V (you sure?) for 3.4Vf. Those LEDs are typically 20mA so figuring that you'll need a 22 Ohm resistor for each LED. That's assuming 3.8V from your battery pack. I'd assume 3.6V nominal, so really you'd want a 12 Ohm resistor for each LED.

Click to expand...

Well it seems my rechargables are a bit overjuiced. Not sure why they read so high:

Regardless, I don't don't know how or where to fit nine resistors into this flashlight. The LEDs are soldered directly into the board.

DrSNAFU said:

Well it seems my rechargables are a bit overjuiced. Not sure why they read so high:

Regardless, I don't don't know how or where to fit nine resistors into this flashlight. The LEDs are soldered directly into the board.

Click to expand...

1/8w resistors are more than enough for this. Ignore the plate that keeps the LEDs separate, get rid of it, clip the anode leg of each LED, use a bit of wire to extend the cathode leg of each LED, and solder the resistor to the anode leg, and mount them raised above the board. There's no heat concern with these LEDs, otherwise they'd have a third solder pad sunk to a layer of copper away from the other conductors for good measure, so leaving these raised a bit above the board is A-OKAY as long as you follow the power dissipation guidelines for the diodes.

Your registered and pictured voltage is within tolerance ranges for NiMH rechargeable batteries. No problems there, you're set just fine for this. Just calculate your resistors to match 3.85V maximum and 3V minimum, anywhere within that range for a resistor is fine, efficiency is dependent upon how closely you match impedance of the resistor to the LEDs desired output.

I have done this, and you may find that a single C cell will fit. Many of those 9 LED cheapies have quite a wide battery chamber which causes some rattle so a C cell will go straight in there. A single AA in a sabot of sorts works as well for IR LEDs.

I sourced my IR LEDs from old remote controls. The one thing to note is that some webs cameras will not pick up 940nm IR even with the IR filter removed.

Mr Floppy said:

I have done this, and you may find that a single C cell will fit. Many of those 9 LED cheapies have quite a wide battery chamber which causes some rattle so a C cell will go straight in there. A single AA in a sabot of sorts works as well for IR LEDs.

Click to expand...

I would go down this route as far as using a different battery like a AA with a spacer "pvc pipe comes to mind" You can get IR LEDs for cheap on fleabay.

Mr Floppy said:

I sourced my IR LEDs from old remote controls. The one thing to note is that some webs cameras will not pick up 940nm IR even with the IR filter removed.

Click to expand...

I would also check this bit out with your web cam, see the test I did on a flashlight I have that I put a IR LED in. The first picture is the camera on the back of my iphone, the IR LED is on but the camera can't see it. The second picture is with the camera on the front of my iphone, that camera is clearly showing the IR LED as being "on". Maybe point your TV remote at the web cam and press some buttons and see if you can see anything on the web cam.



Stoooopid imageshack redid their website and now won't let me resize my images without upgrading my account! I don't want to spend money on a image hosting site! LOL

LEDPunisher said:

1/8w resistors are more than enough for this. Ignore the plate that keeps the LEDs separate, get rid of it, clip the anode leg of each LED, use a bit of wire to extend the cathode leg of each LED, and solder the resistor to the anode leg, and mount them raised above the board. There's no heat concern with these LEDs, otherwise they'd have a third solder pad sunk to a layer of copper away from the other conductors for good measure, so leaving these raised a bit above the board is A-OKAY as long as you follow the power dissipation guidelines for the diodes.

Your registered and pictured voltage is within tolerance ranges for NiMH rechargeable batteries. No problems there, you're set just fine for this. Just calculate your resistors to match 3.85V maximum and 3V minimum, anywhere within that range for a resistor is fine, efficiency is dependent upon how closely you match impedance of the resistor to the LEDs desired output.

Click to expand...

Actually, the plate is made of plastic and meant to go on the front of the LEDs. It's the reflector. The back offers access to the solderings but I'm not sure there's enough room for the resistors AND the battery cartridge back there. The LEDs pictured are the ones I'm going to remove. I'm not sure how I'll be able to get new ones in there without the legs touching the electrodes on the board. There's a little metal dog-leg pictured on the second image in the main post that connects the board's ground lead to the body of the flashlight. Is it possible to just use one resistor there? If the obvious answer is no, then it'll bring home just how much of a noob I am, and I'll gladly express that I have no idea what a solder pad or dissipation guideline is.

Mr Floppy said:

I have done this, and you may find that a single C cell will fit. Many of those 9 LED cheapies have quite a wide battery chamber which causes some rattle so a C cell will go straight in there. A single AA in a sabot of sorts works as well for IR LEDs.

I sourced my IR LEDs from old remote controls. The one thing to note is that some webs cameras will not pick up 940nm IR even with the IR filter removed.

Click to expand...

A c-cell won't fit. I have an adapter that changes AA to C size and that won't slide in there sadly. Maybe I could get a AA in there with the tube method, but would changing to a single AA battery make the project easier?

jason 77 said:

I would go down this route as far as using a different battery like a AA with a spacer "pvc pipe comes to mind" You can get IR LEDs for cheap on fleabay. I would also check this bit out with your web cam, see the test I did on a flashlight I have that I put a IR LED in. The first picture is the camera on the back of my iphone, the IR LED is on but the camera can't see it. The second picture is with the camera on the front of my iphone, that camera is clearly showing the IR LED as being "on". Maybe point your TV remote at the web cam and press some buttons and see if you can see anything on the web cam.

Click to expand...

Yeah I do plan on getting them from ebooy. And I did check my webcam, at first it only showed the IR leds faintly from my remote. After taking it apart and hacking out the IR filter, tv remotes look like bloody strobe lights, really bright. So I think my webcam is good to go.

You can use one resistor, sure! Also, just modify the circuit path on the battery holder to only utilize one section, then you can carry that plus keep two extra batteries stored in the same light!

DrSNAFU said:

ut would changing to a single AA battery make the project easier?

Click to expand...

you can do without the resistors. Ideally you should have a resistor for each LED like the others say but it will work. Using NiMH in these 9 LED things can make individual LED's do strange things but if all your LED's are of the same quality or close, it will be fine. At worse, you change a few burnt ones out but that's like culling the weakest from the herd.

Mr Floppy said:

you can do without the resistors. Ideally you should have a resistor for each LED like the others say but it will work. Using NiMH in these 9 LED things can make individual LED's do strange things but if all your LED's are of the same quality or close, it will be fine. At worse, you change a few burnt ones out but that's like culling the weakest from the herd.

Click to expand...

Now I checked, and my AA rechargeables are about 1.3 volts. I looked and noted some IR LEDs on eblay with a forward voltage of 1.2-1.4 volts. Does that mean I could simply solder out/in some IR LEDs, retrofit the body to hold a single AA (or even AAA since they're rated at 1.28v) and it should work?

Or am I horribly misunderstanding something really basic about electronics?

DrSNAFU said:

Now I checked, and my AA rechargeables are about 1.3 volts. I looked and noted some IR LEDs on eblay with a forward voltage of 1.2-1.4 volts. Does that mean I could simply solder out/in some IR LEDs, retrofit the body to hold a single AA (or even AAA since they're rated at 1.28v) and it should work?

Click to expand...

Yep, but ideally they should have a 1 ohm resistor on each LED. If you measure the resistance in the the circuit for some of these cheap 9 LED lights, you probably will get 1 ohm or more anyway.

Don't over think too much about the voltage of you batteries. You are looking at the open circuit voltage anyway, so under load it will be different. A single AAA will probably sag too much under load to keep 20mA going through the LED.

In any case, IR LED's usually can take a 1.6V max voltage (as in single IR LED in a maglite solitaire with a lithium primary) and 20mA is typically 1.25V so 9 of these typically works ok.

So you're saying just pick up a pack of common IR LEDs, solder them in and power em with a AA? Suspiciously easy...