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I'm trying to make a stationary TV remote control and I'm not noticing the difference between using 12 IR LEDs and 1 IR LED. I still can't get the TV (for example) to get the IR message if the LEDs are not facing the IR sensor on the TV. Whereas the TV remote I already have works fine if its facing the opposite direction. Do I need to use more LEDs or different IR LEDs entirely? The LEDs I'm using are TSAL7400.

The LEDs are arranged like so (12 instead of 20 that are in the picture): enter image description here

I've checked and each LED is getting 100mA when they are on so they are definitely all turning on.

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  • \$\begingroup\$ The problem is not the number of LEDs on the transmitter ( a solution for distance) it is that the receiver is (line of sight) directional \$\endgroup\$ – JIm Dearden Mar 20 '14 at 20:40
  • \$\begingroup\$ It is directional but I assume the IR light can reflect. When I use the TV manufacturer remote it can face the opposite direction and still work (the IR light must be bouncing around the room and eventually reach the receiver). I just want to know if I need to change the arrangement of the LEDs to make the reflection better or add more or change the LEDs entirely \$\endgroup\$ – user2665581 Mar 20 '14 at 20:43
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    \$\begingroup\$ I do the same with my remote but I have to bounce it at specific angles to get the set to work. You can't assume the multiple reflections will eventually (and always) end up at the receiver. As a mythical Scottish engineer once said, "Ye canna change the laws of physics." \$\endgroup\$ – JIm Dearden Mar 20 '14 at 20:57
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    \$\begingroup\$ Some mobile phone cameras are sensitive to IR, you might try using your camera to determine if they're lighting up at all. \$\endgroup\$ – JYelton Mar 20 '14 at 21:11
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    \$\begingroup\$ What wavelength are your leds? What wavelength is the receiver sensitive to? What wavelength is the remote's led? Different sensors, different wavelengths, a reduced sensing capability. \$\endgroup\$ – Passerby Mar 20 '14 at 22:40
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One. It works very well with just one led.

You need one led, not more. If it is not working with one led, then you have different problems. The TV receiver is usually an integrated receiver such as http://www.vishay.com/docs/82491/tsop382.pdf It is quite sensitive, contains an AGC circuit to control the amplification, and works very well even if the infraled light is bouncing off from some walls.

There are two ways to reduce the distance (what you may also see):

  • using a wrong modulation frequency. Although a 38KHz receiver can receive 40KHz signal too, the distance will be much smaller.
  • using wrong light power. It is important that one infrared pulse at 38Khz is a clean pulse, with a 50% pulse width. If you have this many leds, your power supply can easily have glitches. You can see that on scope.

If you show the driving circuit and tell about the power supply, there is a chance we can reveal more potential problems.

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