Electronics > Projects, Designs, and Technical Stuff
Questions about infrared LEDs for remotes
Peabody:
Maybe so. But then "high" isn't actually high, but rather just the 38K carrier being on. The scope did fine reading the IR input which was not demodulated first. Anyway, I've posted on the Arduino forum asking if someone with a real scope could do the same test. That would settle the question.
mikerj:
--- Quote from: Peabody on September 22, 2019, 07:22:25 pm ---My completed remote works, kinda, but the IR isn't getting through as well as it should, and some commands are missed at the receiver. And when I look at the transmitting remote in my camera's live view, I barely see anything, whereas the original Roku remote LED is plainly visible. So I'm not putting out enough IR. Attached is the circuit I'm using, which includes a Darlington. The LED itself is a mystery because I took it from an old remote, which worked fine in its day.
--- End quote ---
Not all IR LEDs have the same peak wavelength, if the LED you found is not matched to the receiver (which most always include an IR filter) then range will be greatly reduced.
Peabody:
A guy on the Arduino forum did the same test, and the output was perfect on his scope. Then I did a bit-banged version of the command, once with the carrier on during the high pulses, and again with the output a solid high during those pulses. The latter show perfectly on my scope, but the carrier version looks messed up. So apparently the problem is indeed my scope. The carrier is throwing it off.
So now I can get back to working on the LED drive.
Peabody:
I ended up, for now, with a 10Ω resistor for the IR LED, and a Darlington with a 2.2K base resistor. That's noticeably brighter when viewed in my camera, and seems to work fine in practice with both the Roku and the TV. I have a 220µFd cap on the power rail, but I'm not sure that's even needed. The power supply is an 18650 with no regulator, and I think it provides current pretty readily for the LED pulses. I don't see any variation in Vcc as the pulses are sent. The final project is here:
https://github.com/gbhug5a/Roku-Sling-IR-Channel-Number-Remote-for-Arduino
tooki:
--- Quote from: Peabody on September 25, 2019, 03:44:49 am ---A guy on the Arduino forum did the same test, and the output was perfect on his scope. Then I did a bit-banged version of the command, once with the carrier on during the high pulses, and again with the output a solid high during those pulses. The latter show perfectly on my scope, but the carrier version looks messed up. So apparently the problem is indeed my scope. The carrier is throwing it off.
So now I can get back to working on the LED drive.
--- End quote ---
Make sure you’re not using an averaging mode. Also, using holdoff might help.
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