IR detector behaviour query

Trying to get a RPM7100 IR detector going (Jaycar cat no ZD-1952). I have the IR source emitting a 38 KHz square wave, as specified, but the device appears to only respond to sudden changes in the received light signal, ie. if I hold it steadily in front of the continuously emitting diode, the output stays high. The data sheet is fairly vague (increasingly common problem?), but it does specify maximum, typical and minimum values for a

600uS 'subcarrier' (my term), suggesting that the device is designed to activate if it receives a 38 KHz carrier that is pulsing on and off every 600 uS.

Checked some other sources, they all bring up the same datasheet.

Can anyone confirm what the behaviour of this device is? TIA

Reply to
Bruce Varley
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"Bruce Varley"

** The datasheet makes it clear the device is designed to sense IR light with a 38 kHz intensity modulation rate further modulated at approx 833Hz with a 50% duty cycle.

It then outputs an 833 Hz square wave.

Any more complex modulation pattern is then up to the designer.

Seems it should be inherently very immune to ambient IR light and various other IR sources with 38kHz intensity modulation.

Did I hear CFLs being mentioned ??

..... Phil

Reply to
Phil Allison

A lot of the IR detectors require you to switch the carrier (38Khz in your case) on and off to represent the ones and zeros that you want to send. The spec sheet will probably tell you the maximum length of carrier on and the minimum length of carrier off times that you need to work with.

Perhaps look at:

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If you don't want to use a carrier then just get an IR photodetector (diode or transitor) and use that.

HTH Alan

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