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I'm doing this project where I control an RC car using infrared. Everything is perfect with 1 IR LED connected to a 220ohm resistor. I'm worried about the range of the signal so I'm thinking of using multiple IR LEDs (let's say 4 to 6 LEDs) to emit the signal.

My problem is achieving this while controlling them through a single pin.

For testing, I tried connecting 2 normal red LED in series through a 220ohm resistor and both of them became dimmer. The LEDs need to be bright.

On hand now I have the IRF520 transistor. Will it work?

I bought my IR LEDs online, while it doesn't say its part number it comes with this description:

  • IR transmitter
  • Emitted color: infrared
  • Lens: 5mm, water clear
  • 940nm wavelength
  • Forward current: 50mA
  • Forward voltage: 1-1.4V
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    \$\begingroup\$ You have to connect them in parallel each with it's own resistor and make sure your pin can handle the combined increased current. \$\endgroup\$
    – Arsenal
    Commented Dec 11, 2015 at 15:50
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    \$\begingroup\$ Arduino pins can only provide 20mA of current, so you'd most likely be better off switching on a transistor, which is connected to the IR LEDs, from the arduino. \$\endgroup\$
    – Funkyguy
    Commented Dec 11, 2015 at 15:52
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    \$\begingroup\$ IRF520 is a poor choice- it doesn't turn on very well with 5V drive. Use a BJT or a logic level MOSFET, preferably a smaller one such as TN0104. \$\endgroup\$ Commented Dec 11, 2015 at 18:40

3 Answers 3

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Typical Collector Follower setup.

schematic

simulate this circuit – Schematic created using CircuitLab

Size the R1-R3 for your leds and current, choose a transistor that can handle that current. A common 2N3904 or 2n2222 type transistor would do for a few leds no problem.

Edit:

The IRF520 N Channel Power Mosfet is overkill for this but as the saying goes, there's no kill like overkill (Yes).

Based on the LED specs you provided, you can skip multiple resistors per 3 leds. (Sized for 40 mA instead of 50mA). Add more in parallel as the other circuit.

schematic

simulate this circuit

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  • \$\begingroup\$ In the edit's diagram the transistor is labeled IRF530. Was that a typo or was it intended to be IRF520? (a quick Google search shows that IRF530 does exist). Also, you mentioned that it is overkill for what I'm trying to achieve. Which transistor would you recommend? I'll be looking for another component for the project in the near future, I can try to look around. \$\endgroup\$
    – Edwin
    Commented Dec 11, 2015 at 16:08
  • \$\begingroup\$ @Edwin that's Circuit Lab's default n-channel mosfet part number. Its just a higher power version of the 520 though. As for common transistors, the two I mentioned are simple general purpose NPN transistors. 2n3904 and 2n2222 perfect for the 40mA that the circuit above shows. \$\endgroup\$
    – Passerby
    Commented Dec 11, 2015 at 16:11
  • \$\begingroup\$ I see. One final question, if I were to extend the number of LEDs (let's say 6), would this diagram be accurate? (Sorry I know nothing about electrical engineering) \$\endgroup\$
    – Edwin
    Commented Dec 11, 2015 at 16:21
  • \$\begingroup\$ @Edwin close. The second resistor should be connected like the first one. One side to the 5V pin, the other to the 1st of the 3 leds in series. Look at the first picture, its like that, but with the 100 ohm resistor and 3 leds instead. \$\endgroup\$
    – Passerby
    Commented Dec 11, 2015 at 16:24
  • \$\begingroup\$ Ah I understand it now. Thanks for the help! I'll be building the circuit tomorrow. \$\endgroup\$
    – Edwin
    Commented Dec 11, 2015 at 16:27
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Everything is perfect with 1 IR LED, connected to a 220ohm resistor.

Infra red LEDs usually are pretty "active" at about 1 volt so, if you have a 5V GPIO pin you can use 4 in series and a smaller resistor (56 ohm) to control the current. This means energy saving too.

enter image description here
(source: mec1995 at www.sentex.ca)

To do this answer more justice I'd need to know the LED part number (data sheet required) and what the GPIO voltage and current is.

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  • \$\begingroup\$ I've edited the post and added some information about the IR LEDs \$\endgroup\$
    – Edwin
    Commented Dec 11, 2015 at 15:58
  • \$\begingroup\$ That tells me nothing I couldn't have guessed. What about the all important info I asked for i.e. a part number? \$\endgroup\$
    – Andy aka
    Commented Dec 11, 2015 at 15:58
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    \$\begingroup\$ @Edwin Are you aware that putting them in series will save wasted energy being dissipated in the 220 ohm resistor, especially if they are put into parallel operation? Important for a battery powered application. The same 18 - 20 mA drives several LEDs in series. \$\endgroup\$
    – Andy aka
    Commented Dec 11, 2015 at 16:00
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I’ve been building IR lights for my night paranormal investigations, and have used up to 6 by wiring in parrallel with a resistor before the diodes. While the forward voltage is only 1.6 I’ve ran it off a 12v system consisting of the 8 pack of AA batteries. I also have a 12v pigtail I can use for the wall charger if I just want to use direct current.

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