Tagging wildlife is never straightforward in the best of times, but it becomes a great deal more complicated when you’re trying to track flying insects. Instead of trying to use a sensor package, [DeepSOIC] attached tiny, light retroreflectors to bees and hornets, then used a pulsed infrared light mounted on a drone to illuminate them. Two infrared cameras on the drone track the bright dot that indicates the insect, letting the drone follow it. To get a spot bright enough to track in full sunlight, though, [DeepSOIC] had to drive some infrared LEDs well above their rated tolerances.
The LEDs manage to survive because they only fire in 15-µs pulses at 100 Hz, in synchrony with the frame rate of the cameras, rather like some welding cameras. The driver circuit is very simple, just a MOSFET switch driven by an external pulse source, a capacitor to steady the supply voltage, and a current-limiting resistor doing so little limiting that it could probably be removed. LEDs can indeed survive high-current pulses, so this might not really seem like component abuse, but the 5-6 amps used here are well beyond the rated pulse current of 3 amps for the original SFH4715AS LEDs. After proving the concept, [DeepSOIC] switched to 940 nm LEDs, which provide more contrast because the atmosphere absorbs more sunlight around this wavelength. These new LEDs were rated for 5A, so they weren’t being driven so far out of spec, but in tests they did survive current up to 10A.
We’ve seen a similar principle used to drive laser diodes in very high-power pulses a few times before. For an opposite approach to putting every last bit of current through an LED, check out this low-power safety light.
It’s not clear from the text whether the shutter (camera exposure) time is the 50 us, or whether only the LED is on for that duration. If you operate it like those welding cameras mentioned, the camera has a very short shutter time and “blind” to sunlight for most of the time, and is integrating light only when the LED is illuminated.
Depending on how much the scene changes from frame to frame you can also increase the conspicuity of the retroreflection a lot by subtracting a previous “no flash” frame from the “flash” frame. If you have enough processing horsepower to do scene tracking and registration before subtraction, even better.
Pushing more current through a LED than datasheet specs certainly is in the “abuse” category. Very often it’s also quite senseless, as the efficiency of the LED goes down when over driven. You do not get 2x the light output when pushing 2x the current though a LED. From the (limited) experience I have datasheet values already seem a bit optimistic, and LED efficiency already starts deteriorating at around 60% of the rated current. But there are of course always exceptions, and some LED’s are designed for pulse rated use. And a good datasheet does of course have these values.
LED’s are also not very expensive anymore, and thus adding more leds at a more moderate current extends battery life for the same light output.
It’s also relatively easy to make some usable measurements yourself. You can use a light sensor, and measure it’s response with a fixed LED current but with different distances from the LED, and then you can repeat those measurements with a different LED current.
Cool, but if your goal is something like a single-cell flashlight that comfortably fits in a shirt pocket yet has enough output to melt holes through a credit card, how do you do that without blatantly disregarding everything in the LED’s datasheet? Three Cree XPLs (R.I.P.) on a direct-copper board, with a direct-drive driver using a super-low Rdson FET, and PWM modes from attiny13, powered by an unprotected 18650 like Molicel P30B… these things will draw more than 20 amps, yet the lower modes are still perfectly usable as a ‘normal’ flashlight. I’ve built many of those, and have one example I have carried every day for at least the past 8-9 years with zero component failures.
Aren’t most IR LED are designed specifically for pulse operation? I thought they were.
So you should not compare them to visible light LED for that reason alone already.
And they are in general different from visible/UV LED.
And the pricing for high power IR LED is different too.
Watching the video made me feel sad for the hornet, he’s like a human and can hardly escape tracking, more so because of the stuff attached to him, again like humans.
And of course the music enhanced that feeling.
We used to do this the analog way on the farm when hunting down underground wasp nests. Catch a wasp, stick it in a jar with sone flour. Shake it and release. Way easier to follow a white wasp against a green or wooded background. The abduction and flouring seemed to make them want to head home straight away (who wouldn’t I guess). Once we’d located the nest it was off to the workshop for the oxy acetylene cart and some bad life choices :-)