IR beam circuit - need to know how it works - Electronic Circuits Projects Diagrams Free

ant9985 · 11th June 2006, 11:58 AM

hi, could anyone give me a detailed description of how this circuit works and where the bandpass filters are plz. circuits are in the link below:

http://www.ee.washington.edu/consele...inal/final.htm

this is the discription iv got now, but its sketchy on some parts and i dont know where the bandpass filters are(what parts they consist of)
im not even sure if its entirely correct. thnx a lot.

Description
The emitter uses a 555 timer to turn on and off the IR LED at a rate of 5khz. This sends out a 5khz square wave. By emitting a 5khz signal, the detector shouldn’t pick up any light sources other than the signal from the IR LED.

The detector receives the signal and sends it to an Op. Amp to amplify the incoming signal, after the first Op. Amp there is a bandpass filter which snubs out any signal received that isn’t at 5khz, which the emitter outputted. After the second bandpass filter, the signal is sent into a comparator.

If the - input to the comparator is greater, then the output will be -12 volts. If the + input is greater then the output of the comparator will be +12 volts.

The output of the detector will always put out either 0 volts, 12 volts or –12 volts, 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 +12 volt and –12 volt peaks.

audioguru · 11th June 2006, 12:29 PM

They removed the bandpass filter because it didn't work. It was replaced by a highpass filter with the 0.47uF capacitor, and a lowpass filter with the 220pF capacitor. This makes a very poor bandpass filter so other frequencies can easily be detected.

The output opamp has a gain of a few hundred thousand so its output voltage is either near +12V or near -12V, never near 0V.

ant9985 · 11th June 2006, 12:35 PM

ok, so the high pass and low pass filters act as a bandpass filter but dont actually work?

**Nigel Goodwin** · 11th June 2006, 12:53 PM

The whole 'design' is really poor, I'm presuming they didn't pass the course with such a poor effort?.

Whatever you're trying to do (and you've not mentioned it!), this isn't the way to do it!.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

11th June 2006, 11:58 AM	(permalink)
ant9985	IR beam circuit - need to know how it works hi, could anyone give me a detailed description of how this circuit works and where the bandpass filters are plz. circuits are in the link below: http://www.ee.washington.edu/consele...inal/final.htm this is the discription iv got now, but its sketchy on some parts and i dont know where the bandpass filters are(what parts they consist of) im not even sure if its entirely correct. thnx a lot. Description The emitter uses a 555 timer to turn on and off the IR LED at a rate of 5khz. This sends out a 5khz square wave. By emitting a 5khz signal, the detector shouldn’t pick up any light sources other than the signal from the IR LED. The detector receives the signal and sends it to an Op. Amp to amplify the incoming signal, after the first Op. Amp there is a bandpass filter which snubs out any signal received that isn’t at 5khz, which the emitter outputted. After the second bandpass filter, the signal is sent into a comparator. If the - input to the comparator is greater, then the output will be -12 volts. If the + input is greater then the output of the comparator will be +12 volts. The output of the detector will always put out either 0 volts, 12 volts or –12 volts, 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 +12 volt and –12 volt peaks.

11th June 2006, 12:29 PM	(permalink)
audioguru	They removed the bandpass filter because it didn't work. It was replaced by a highpass filter with the 0.47uF capacitor, and a lowpass filter with the 220pF capacitor. This makes a very poor bandpass filter so other frequencies can easily be detected. The output opamp has a gain of a few hundred thousand so its output voltage is either near +12V or near -12V, never near 0V. __________________ Uncle $crooge

11th June 2006, 12:35 PM	(permalink)
ant9985	ok, so the high pass and low pass filters act as a bandpass filter but dont actually work? Last edited by ant9985; 11th June 2006 at 12:39 PM.

11th June 2006, 12:53 PM	(permalink)
Nigel Goodwin	The whole 'design' is really poor, I'm presuming they didn't pass the course with such a poor effort?. Whatever you're trying to do (and you've not mentioned it!), this isn't the way to do it!. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk