Help with IR motion sensor

[slackjack]

I'm trying to buld this



Left = transmitter
Right = receiver

This circuit has a transmitter and a receiver. So from what I understand, the interruption in a modulated pulsating beam that is transmitted by an infrared diode and received by an infrared transistor sets off the alarm. So what I am looking at is two different circuits. Can't these two be integrated into one circuit?
So I absolutely must have the circuit with the Photodiode right? If they cant be integrated, how must the receiver be placed with respect to the transmitter?

What are some uses of a Phototransistor?

--thank you 8)

[ante]

Hi jack,

What would be the point of integrating the two circuits? What would you use it for then?

[audioguru]

If the circuits were integrated side-by-side and pointing in the same direction then they could be beaming and receiving the IR from a mirror on the other side of a corridor to be monitored. An intrusion would break the beam and signal the alarm.
If the intruder had his own mirror or modulated IR beam then he could easily not be detected. ;D

[stevedabear]

What confuses me about this system, is that ii cant see that it would stay on once it has been tripped... Surely it would be best fed into a locking transistor ? with a reset... just a thought.

[audioguru]

That's correct. The circuit doesn't have a latch on its output so it could be used to count cars driving by or somethin'.

[slackjack]

Hi jack,

What would be the point of integrating the two circuits? What would you use it for then?

I was just asking if its possible. Mayb it would just be easier to build one circuit instead of two...or did I miss something.

[slackjack]

So without the latch, the output would not remain high when its activated right? What kind of latch do you recommend. Probably a NOR latch?

[audioguru]

So without the latch, the output would not remain high when its activated right? What kind of latch do you recommend. Probably a NOR latch?

Correct. Make a latch with a pair of cross-coupled NOR gates. Consider using power-up reset and a manual reset. ;D

[Shahriar]

You can Also creat a latch with D-Filp Flops. 7475. (Check it!)

Anyway, there is a project in the Project section of this site. Its name is Park-Aid. Take a look. It will anserw to some of your questions.

HTH - Shahriar

[slackjack]

Thanks for the link Shahriar. It seems they have integrated the emitter and receiver circuits.

D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it.

All what this circuit does is detect an object as it moves toward it, in this case the car right? If thats so, then this circuit would do just fine for experimental purposes. A vehicle is relatively wide though. Would it detect a person just as good as the car?

[audioguru]

The Park-Aid circuit detects the strength (which is also its distance) of the IR beam reflected from a mirror (or white paint) on the wall. If something blocks the beam then its output indicates it as no received reflected IR signal. It would easily detect a person.