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pfcs49 28th February 2008 10:47 PM

infra-red detectors
I want to source an IR detector that is compatible with the one in my NAD L40 receiver so I can put it on the rear of the receiver and mount a mini-toggle and jack for it at the rear of the chassis.
The existing sensor is cylindrical/yellow, about 3mm dia, 7mm L, has 2 pins, has 10.8mV across it w/power on and doen't seem to express polarity thru ohmeter.
I don't want to use a repeater system.
Digi-Key seems to have many, but which to choose? Phil

gmphadte 5th March 2008 05:07 AM

They have a number on them but what u intend to do may not work.

Gajanan Phadte

edit:two mirrors will do the trick without opening the unit.

pfcs49 6th March 2008 12:33 AM

If the replacement sensor has the same values as the original, I don't see how it can't work.
The window between the two spaces is plexiglass type; I've tried a mirror in various sensible positions, but it doesn't work through the window although it works fine in the room.
so-how to pick a sensor-help! phil

gmphadte 6th March 2008 09:00 AM

pfcs49 wrote

If the replacement sensor has the same values as the original, I don't see how it can't work.
I hope electronics was that easy to design and modify

Gajanan Phadte

pfcs49 6th March 2008 12:53 PM

the modification consists of extending the wiring 18" to the "stock" replacement sensor. tell me how that's a problem.
The problem is matching the sensor. phil

gmphadte 7th March 2008 04:19 AM

Yes, the wire length is the problem, as any wire will act as an antenna and pickup surrounding interference. The interference is always present inside and also outside the box. Besides these sensors like clean power.

These are some of the suggestions for modifying assuming the sensor has 3 pins...
Use shielded cable for extending - 3core plus shield
Connect shield to ground pin of the original sensor and leave other end open and insulate it.
Use 10fd and 0.01 to 0.1 fd ceramic capacitor across the supply pins of and close to the add-on sensor
Use changeover switch on the outputs of the sensor.

Best of luck

Gajanan Phadte

Conrad Hoffman 7th March 2008 05:07 AM

If one was an optimist, they might be using a photodiode, all of which are IR sensitive. It isn't black, so it doesn't have a visible filter- maybe a red or black window on the front of the unit?

They might be going into a current-to-voltage converter (- pin of an opamp), so pickup wouldn't be a problem. Just parallel another photodiode with it and see what happens. I'd surround it with some kind of filter to knock out ambient light, but since the remote signal is ac, they probably just ac couple it and ignore ambient.

If the remote sends a code, don't try to filter the diode, or you'll filter out the signal you want. It's worth a try, as you're unlikely to hurt anything, but don't be too unhappy if it doesn't work, as all of the above is a wag. A schematic of the circuit would help immensely.

As for what part to pick, throw a dart. Something that looks physically similar will have a similar size die.

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