Electronics Oppos help?

"Smallbear wants a modern Syclone, local Maple Leafs spammer" (smallbear94)
09/16/2016 at 12:25 • Filed to: None

So, I converted an old digital camera to an IR camera a while ago. Gets some pretty cool pictures. But really what I want from it is to use it at night with IR illumination. SO:

I bought one of these. !!!error: Indecipherable SUB-paragraph formatting!!!

I was planning on swapping the LED’s for IR LED’s, but I don’t know which LED’s and what resistors I need to get to make it work properly. As it stands it has four LED’s powered by four CR2032 3V batteries.

All I know about it is that LED’s aren’t plug and play units and I don’t exactly know what I’m doing with them...

DISCUSSION (9)

jimz > Smallbear wants a modern Syclone, local Maple Leafs spammer
09/16/2016 at 12:29

you could build it yourself with a little project board and some IR LEDs. The calculation for the correct current limiting (ballast) resistor is simple; R = (Vs-Vd)/Id, where Vs=supply voltage, Vd=LED rated voltage, and Id=LED rated forward current. if you want to put multiple LEDs in series, then you sum the LED’s voltage drops.

it’d be kind of difficult to retrofit them into that light you linked; a lot of those white LED lights powered by coin cells have no ballast resistor, they just rely on the internal resistance of the battery. which also has the effect of making the battery’s voltage sag when the LED is lit. An IR LED is likely to have a much lower rated voltage than the ultra-bright blue LEDs used to make white ones.

JawzX2, Boost Addict. 1.6t, 2.7tt, 4.2t > jimz
09/16/2016 at 12:36

Yes, like JimZ said.

Most IR LEDs have low rated voltage and/or forward current. They tend to be *VERY* efficient and require very little power for the amount of (invisible) light they put out. Also search your IR LEDs carefully, many are designed for remote controls and have very narrow (10-15 degree) beam patterns, which is great for making an effective long-range remote control, but very poor for lighting a scene.

these look like a good starting point if you’re not affraid to spend $20+ on your project...

http://www.ledsupply.com/leds/osram-gol…

these are a little cheaper...

http://www.ledsupply.com/leds/cree-xlam…

Smallbear wants a modern Syclone, local Maple Leafs spammer > jimz
09/16/2016 at 12:43

Would they usually be wired in series?

This for example:
https://www.adafruit.com/product/387

Actually has a 1.6V forward voltage. If I had all 4 LED’s in series with the 4 batteries, would that be (4V-1.6V)/100mA=0.024, just one resistor for all 4? I feel like I’m doing this wrong.

The reason I want to retrofit this one is because of the camera mount. I could make one myself but I’d rather use the existing one if I can...

jimz > Smallbear wants a modern Syclone, local Maple Leafs spammer
09/16/2016 at 12:53

your mistake is dividing by the milliamps; you need to divide by the current in amps, so divide by 0.1. also, the sum of the LED’s voltage drops can’t exceed the supply voltage otherwise you’ll get little to no light out of them.

edit: cripes, I don’t know if CR2032s can even supply near 100 mA continuous...

edit edit: nope. they’re only 240 mAh at 0.19 mA (0.0019 A) current draw. if those IR LEDs can safely draw 100 mA they’d tank CR2032s in no time.

Smallbear wants a modern Syclone, local Maple Leafs spammer > JawzX2, Boost Addict. 1.6t, 2.7tt, 4.2t
09/16/2016 at 12:56

I found these:

https://www.adafruit.com/product/387

1.6FV 20deg beam. They LOOK like they’d work, but then that’s why I’m asking first...

I’ve been trying to stay away from the 850nm LED’s as apparently they still glow slightly and I don’t want that.

As far as spending money, I’ve probably put $35-40 into the project, so it would be nice to do it cheap. I don’t mind spending the money if it comes to that, but I also don’t want to spend it twice.

Smallbear wants a modern Syclone, local Maple Leafs spammer > jimz
09/16/2016 at 13:03

OK, so I definitely have to find something less robust if I’m going to do it this way.

And the voltage drops: you mean add the forward voltage of all 4 together, or is there something else to consider?

And thanks, this is a huge help.

JawzX2, Boost Addict. 1.6t, 2.7tt, 4.2t > Smallbear wants a modern Syclone, local Maple Leafs spammer
09/16/2016 at 13:13

yeah, those would probably work... 20-degrees is a pretty narrow beam, but those look like a robust LED and should throw with good reach.

jimz > Smallbear wants a modern Syclone, local Maple Leafs spammer
09/16/2016 at 13:14

yes. but it’s wise to make sure you still have some “room” between the sum of the forward voltages and supply voltage; LEDs are “negative temperature coefficient” devices and as they heat up they draw more and more current until they burn out, so you still need some form of current limiter. I don’t know how much room that thing has inside, but you could theoretically gut it and use a 9V battery. Then your calculation would be (9-(1.6*4)/0.1 = 26 ohms. You’d definitely want to use at least a 1/2-watt resistor.

Smallbear wants a modern Syclone, local Maple Leafs spammer > jimz
09/16/2016 at 13:23

It doesn’t have room inside, but I could piggyback it underneath. That would still be easier than building from scratch.

But it doesn’t look like a 1/2W 26 ohm resistor is going to be easy to find... maybe if I wired them in 2 separate circuits, 2 LED’s each, and used 1/2W 58 ohm resistors instead it would work. I did find those ones.