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I have a pair of IR transmitters and receivers, but I have found that the brightness of the transmitter is very low, so that I can't use it to detect an object in front of them.

What should I do?

  • Please specify the part(nr) you are using. – Gerben Mar 19 '16 at 15:28
  • ? Anyway, how is your Arduino connected? Try using an external power supply (5V) to connect your IR transmitter. – Paul Mar 22 '16 at 11:42
  • A schematic would help. We have no idea of what transmitters you are using, whether or not you are using driver transistors, and what part numbers you are using. Adafruit has an example which sadly does not have a current-limiting resistor for the LED. However the idea of using a transistor to increase output is sensible. – Nick Gammon Mar 26 '16 at 6:39
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IR transmitter LEDs are literally just LEDs that emits Infrared Light which is not visible to the human eye. That being said, IR LEDs behave very similarly to regular LEDs and therefore to increase the brightness you need to increase the Voltage it is receiving, just like you would do with a regular LED.

But the problem with LEDs is that they drain current and that's why we use resistors,to protect our electronics(i.e. Arduino).

So to recieve maximum voltage you can reduce the resistance of the resistor (let's say 220ohm or even 100ohm).

Forgot to mention that the correct wiring of LEDs to an arduino is as follows:

5V pin(or digital pin set to high) -> Anode leg(longer) of LED -> Resistor(connected to shorter leg :3) -> ground pin

  • That is indeed a correct way. Others are: Anode to +5, Cathode to resistor to I/O pin (LOW pin enables, HIGH pin disables the LED). The resistor can be on the Anode side or the Cathode side of the LED; it is absolutely irrelevant which way it is done. – JRobert Mar 19 '16 at 16:40
  • Actually you need to increase the current not the voltage. Increasing the voltage without changing the resistance has the knock-on effect of increasing the current. Or you can decrease the resistance and keep the voltage the same to increase the current. Either way you are limited to either the IO pin's absolute maximum (40mA) or the LEDs absolute maximum, whichever is lower. – Majenko Mar 19 '16 at 17:45
  • @Majenko True. But I thought that because the resistor and LED are in series then they should Hv an equal current draw. But the you are right because the LED and resistor act like one load and voltage is constant . So the only way to increase power is by reducing resistance. – Mero55 Mar 19 '16 at 17:48
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If you aren't at the current limit of either the IO pin (40mA) or the LED (usually around 30mA) you can increase the current as far as the lower of those. That can be done by reducing the value of the resistor you are using with the LED or using a higher current drive circuit.

However, just having an LED turned on all the time is not a good way of using it - you are constantly fighting against the background light.

Instead the LED needs to be pulsed on and off using PWM at a very high frequency (typically 30-50kHz) and you need to detect that pulsed light with the receiver.

This is usually achieved by using a high-pass (or band pass) filter and amplifier on the receiver.

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