wondering how this circuit works...

[ant9985]

hi, i was thinking of building an infrared object detector like the one on this webpage. i was wondering, would anyone be kind enough to give me a detailed description of how the emiter and detector circuits on this page work? :?

**broken link removed**

also, would it be possible to attach a sounder on the output?

 

[plot]

Well, the Emitter uses a 555 timer in order to turn on and off the IR diode at a rate of 5kHz. This basically sends out a 5kHz square wave from the IR diode. Pretty simple.
The reason they decided to make it output a 5kHz signal apparently, is so the detector wouldn't pick up any outside sources of IR light, it'd only look for a 5kHz signal of IR light.


The detector receives the signal, sends it into a OpAmp to amplify the incoming signal, after the first OpAmp there is the bandpass filter which snubs out any signal received that's not at 5kHz, which the emitter outputted. After the second bandpass filter, it sends the signal into a comparitor... basically a comparitor is an OpAmp that's always going to be saturated unless both inputs are equal. If the - input is greater, then the output of the comparitor will be -12 volts. if the + input is greater, then the output of the comparitor is going to be +12 volts.

So, the output of the dector will always put out either 0volts, 12 volts, or -12volts, depending on which part of the signal is received... so when an IR signal is detected, the output of the entire detector will be a 5kHz signal with +12volt and -12volt peaks. You can hook this into whatever you want... there's no real apparent reason for doing it this way unless the next stage wants 12 volt swings.

 

[ant9985]

ok, thnx very mutch