I need to buy some IR LED Detectors but I am having a hard time finding anything except for the 940nm. It seems that there are only three types of IR LED emitters and detectors sold. 850nm, 880nm & 940nm. Is this correct? My main question is can I use a 940nm detector with the 850nm and 880nm? Will it detect those two? Can anyone recommend a place to get IR LEDs that has all of these?

I use them because I service redemption and other coin-op games. Many times these things are used in the games but they don't tell you what the part number is. I needed to replace two pairs on a game the other day and they wanted $55.00 for it. That was four LED's mounted on a short wiring harness. So I want to stock up on all of the likely IR LEDs and then swap them in until I get the game working.

Thanks again Russ

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    \$\begingroup\$ What type of IR detector - photo-transistor or photo-diode? \$\endgroup\$ – Leon Heller Jul 19 '10 at 23:25

No, there are more than 850, 880, and 940nm transmitters: the IR spectrum ranges from 700nm to 1mm. A distinct set of values is sold, typically in the 700 to 1400 nm range (IR-A), where 850, 880, and 940 are common values. Here's a selection of the Mouser listing of IR emitters. I've used the TSAL series of emitters from Vishay, although I'm not sure that they're in your current, brightness, or bandwidth specs.

The parameter you're interested in for transmitters is the "Relative Radiant Power vs. Wavelength", and for receivers, you want to know the "Relative Spectral Sensitivity vs. Wavelength". For instance, the bell curve in Fig. 9 of the datasheet for the TSAL6100 shows that it has a relative intensity of 1 at 940nm, and outputs about 0.125 times this intensity at 890 nm. That likely means that it's not bright enough to use with an 850 nm detector, and would be iffy at best with an 880nm detector.

On the plus side, receivers are usually more generous, for example the TSOP348 detector [picked at random] has a spectral sensitivity of better than 80% for all wavelengths between 850 and 1050nm. Taos Inc. also makes some nice digital, analog, and frequency output detectors for many wavelengths; I've used them with good success before. This will help you if you need to replace a sensor, especially if it's just used as an on/off digital sensor, for instance in a light curtain application, because 80% is pretty close to 100%.

However, that sort of receiver will only tell you about the quantity of light. If you knew that your LEDs were the same brightness (you don't), then you might be able to infer a frequency (i.e. this one is 75% as bright as the 950nm, therefore it's about 820 or 1070nm). You can also determine that an LED is on with just a digital camera, like the one in your cell phone.

Color Sensors
An infrared camera could tell you the wavelength after compensating for temperature, but would not fit most budgets. (Note: These are awesome for determining all kinds of things - Night vision, temperature gradients, etc.)

What you need for that is an color sensor in the infrared range. A color sensor will have multiple narrow-band and/or filtered detectors, so that you can determine the color of the light. See Figure 1, Photodiode Spectral Responsivity" of the datasheet for the TAOS TCS3200D[pdf] for an example (No, it's not going to be a pretty algorithm...). However, you'll notice that the visible light filters stop at about 750nm, and everything goes back to the same curve. Finding a color sensor that works into the infrared range is left as an exercise to the reader, but this sort of IC is what you're looking for.

An alternative to an IR color sensor (which may not exist) would be to use a broadband sensor with a set of infrared transmitting filters tuned to the region of the spectrum which you need. A quick Google search turned up this page, you'll probably find something better.

As for distributors, I find that Mouser has a better selection and cheaper prices on optoelectronics than Digikey.

  • \$\begingroup\$ Thank you everyone. Thanks for the link to Mouser. I always have trouble finding things at both Mouser and Digikey. Mouser has the Largest selection between 850nm-940nm, Should the TSOP348 or something just like should detect the 850m 880, 940nm emitters? Is there an inexpensive test instrument that can show me the wavelength of an IR LED? Thanks again Russ \$\endgroup\$ – Russ Jul 20 '10 at 15:25
  • \$\begingroup\$ If you have the time and the parts, build one yourself. For testing what kind of transmitter you have, get one of each detector, and build a circuit which measures their responses relative to each other (microammeter or something...) For a transmitter, have a circuit with a switch to select each diode, and a rheostat and ammeter to test at which point you get a satisfactory response. Lowest current here wins. \$\endgroup\$ – Jesse Jul 20 '10 at 16:23
  • \$\begingroup\$ @Jesse - No, the detectors are generally too broadband for that purpose. In addition, you can't know which side of the detectors' peak value that the frequency lies. You do need multiple detectors, and you need to filter them. This is packaged as a color sensor. You could build your own, but it would be tedious and hard to calibrate. \$\endgroup\$ – Kevin Vermeer Jul 20 '10 at 17:22

Some IR receivers are more than just a photodiode - they also demodulate the IR carrier. Make sure you also look at the carrier frequency for the IR as there are a few variants with that as well - 38kHz seems to be the most common.

There is some info on Wikipedia here


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