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I'm building a IR hub to control several LEDs stripes, and a projector in a room and noticed that my IR transmitter works even when VCC is not connected.

Should I wire it in anyways? Why is it there? What does it do?

This is the IR transmitter I have.

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  • \$\begingroup\$ Include the datasheet of that module. Oops! It's a "Cheapy-Chinese" module and there is no datasheet. Just buy one, reverse engineer it's schematic and post that here then perhaps we can tell you why VCC isn't needed. My guess is that on the module it is not connected. \$\endgroup\$
    – Bimpelrekkie
    Sep 23, 2019 at 14:01
  • \$\begingroup\$ You're probably right. I used the connectivity thing on a voltmeter (the one that beeps when connected) and couldn't get a beep on none of the little things on the board. Figured I'd ask. - Sorry for using improper terms, I just don't know what half of the things are called. Thank you! \$\endgroup\$
    – Matthew Abrman
    Sep 23, 2019 at 14:05

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Ideally, the IR-led is powered by a VCC line, capable of delivering the ~60mA a infrared LED generally needs. This should be done by a MOSFET, which is essentially a switch, which switches on and off based on the data line, which is connected to the gate.

In the case of your IR transmitter, no MOSFET can be seen. It means that the IR-led is directly fed from your data line. It works, because your data source can deliver enough current. It's generally not the way you'll want to switch an IR-led on and off. Hence the fact you can detach your VCC line: it's not being used.

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You power it from the data line connected to the uC pin it is called parasitic power and it is definitely very dangerous for your uC.

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  • \$\begingroup\$ What does uC stand for? Should it be of concern? I just started with Arduino without proper schooling so I'm learning as I go. \$\endgroup\$
    – Matthew Abrman
    Sep 24, 2019 at 15:34
  • \$\begingroup\$ uC means microController. So it is your atmega there. max pin current is 16-20mA depending on the model. Your IR diode myy consume up to 60mA. Do you think that they give max pin current for no reason? Saying it quicker you can kill your atmega \$\endgroup\$
    – 0___________
    Sep 24, 2019 at 16:12
  • \$\begingroup\$ It's actually ESP8266 on a WeMos D1 board. I read that the maximum current that can be drawn from a single GPIO pin on ESP8266 is 12mA, that doesn't sound good. I run them in a setup based on this guy's comment -> github.com/z3t0/Arduino-IRremote/issues/… . I didn't find a better way to run 5 IR transmitters off of one board other than this (because of IR and chip clock speed?) Then again, they only flash once in a while - can that still damage the ESP8266? \$\endgroup\$
    – Matthew Abrman
    Sep 25, 2019 at 17:09
  • \$\begingroup\$ yes it can, I adraid \$\endgroup\$
    – 0___________
    Sep 25, 2019 at 18:49

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