IR Tripwire

Hey guys, I'm trying to setup a dual tripwire setup for entry/exit detection however I'm having a hard time getting the tripwires to work right.

I'm using a PIC microcontroller to generate a 38khz signal at 20% duty cycle to power my IR emitter which is then amplified by a transistor, not really sure at what gain right now. Then i'm using a TSOP382 IR receiver to pick up the IR signal.

The issue is that when I trip it frequently the system works great, however if I leave the tripwire untripped for a minute then try to trip it, the receiver takes a few seconds to realize it's been tripped, what gives? there's no capacitor on the output (at least not in my circuit)

Has anyone experienced this issue or have any advice on what to do next?

I've not done much testing but even when it trips quick it's not instant (seems like there's a few ms delay, but that could just be arduino/serial delay so not worried about it yet). I must be doing something wrong.

These devices are designed for short bursts of pulses used for remote control. The specification says:

“Some examples of disturbance signals which are suppressed are:
• Continuous signals at any frequency”

After it sees a long burst (>70 cycles at 38KHz, about 2 milliseconds) it ignores that signal until that signal has been gone for four times the burst length.

You need an IR receiver designed for continuous signals.

Then i'm using a TSOP382 IR receiver

Are you sure? I don't recognise that number.

The one you need is a TSOP4038 IR receiver, that is designed for your application.

Hm, I'll take a look at that. thanks

Here's where I got the tsop382 http://www.sparkfun.com/products/10266

Do you guys have any suggestions on the emitter? I was thinking something like this maybe: http://www.newark.com/vishay-semiconductor/tsts7100/ir-emitter-950nm-4-7mm-to-18-2/dp/33C1872 it's got a nice focused beam

You haven't got a TSOP382 it is a TSOP38238, the last two digits give the modulation frequency. What you have to look for in an emitter is that it's peak emittance wavelengths match each other.

Ah, hah, yeah I just got the name straight from the sparkfun page, not where they have the datasheet listed.

Either way, yeah after reading the datasheet closely I see it has filtering but the one you recommended specifically says that it doesn't filter constant 38khz signal so ordered a few of them.

Thanks again guys!