TSOP1738 when used as a Beam Break Detector
by ericgibbs , 30th November 2011 at 12:12 PM (1332 Views)
When using the TSOP1738 IR Receiver Module in a Beam Break application it is necessary to interrupt the 38KHz signal being generated by the IR Emitter.
An example is a 'People In/Out Counter', where the beam break is used to detect a person entering or leaving a room.
If the TSOP detects a continuous 38KHz pulse if will consider it as a interference source and will not work as expected.
[refer to the attached extract from the TSOP datasheet]
The attached circuit transmits at 38KHz, with a break in the transmission at approx 650Hz.
This gives a group of ~45 IR pulses, with a gap equal to ~ 20 pulses.
The circuit shows two options for the LED IR driver.