IRED Distance Meter 1

[Umar]

I made an IRED distance detector circuit based on MX-171 AF IC from Macronix. I have covered the Photodiode and the IRED LED with a filter. The filter is a focusing lens with IRED-pass-filter material. It works perfectly in indoor. But it really unstable when I tried to use it outdoor. I live in Indonesia, country with very bright sunlight.
Any comments or suggestion ? Thank you. :

 

[nbucska]

I suggest use pulsed high-current IR with AC coupled
narrow band amplifier at the receiver side.

<nbucska@pcperipherals.com>

 

[IRstuff]

> Use more and better filtering. The transmitter diode is very narrow band, so you can get by with less than 0.1 um bandwidth on the receiver filter.

> Bear in mind that daylight ranging is extremely limited, given the available power that you probably have to play with.

> Use a retroreflector material such as bicycle tail reflector or Scotchlite. Most laser rangefinders use similar reflectors to get adequate performance for longer ranges and daytime.

> If you are trying something that's significantly difficult, you may need an APD or photomultiplier as a detector.

TTFN

 

[rickcappels]

One other thing you can do is remove the filter from the IRED. Though it is an IR pass filter, it is attenuating some of the llight (even clear glass looses about 8% to reflection losses), and it serves no practical purpose, so loose the filter on the transmit side and get a little more power to work with..

You did not decribe your receiver circuit, but AC coupling is good, but also including a bias loop (a slow loopo, something like an AGC) to make sure there is always enough voltage across your diode may help as well.

Two other solutions: Come on up to Thailand where its cloudy all day, or use it at night

Good luck.

 

[BrianR]

I have made devices like this before and noted that there is a great deal of infrared from the sun around the 900-1000 nm region where these IR relay devices operate. Filtering helps a bit but restricting the viewing angle of the detector so it only sees the transmitter and not other areas illuminated by the sun, helps more, (make it look through a tube).

Also modulating the transmitter beam and using a receiver tuned to the modulation frequency really made a difference.

 

[IRstuff]

I agreee, but bear in mind that the narrower the field of view of the receiver, the hard to align the transmitter to the receiver.

Also, pulsing the signal must be coupled with a matched filter input with no more bandwidth than absolutely necessary to minimize the noise bandwidth.

TTFN

 

[rickcappels]

Yeah, its a good idea to filter the receiver, but doesnt' do any good to filter the transmitter.