Hi,
Can someone please provide me with a diagram of a circuit that I can use to detect the output from an IR diode which is being switched with an underlying frequency of around 36KHz. The output from the LED will be on/off pulses, each pulse having a period of say, 200ms. When the LED is 'on' it will be sending IR out at a frequency of about 36KHz.
What I need to do is detect when the beam from the diode is interrupted.
I've been trying to do something similar using a specialised IR receiver chip (ZD-1952) but without success. I thought that going back to basics, using an IR phototransistor, some kind of amplifying circuit, and a filter should let me detect the square wave that I will be emitting from the diode. Once I have the waveform reconstructed in the receiver, I can then use the 555 'missing pulse' circuit to detect when the beam (pulse train) is broken.
However, the part I don't really understand is how to filter the signal being received by the IR photo transistor, so that only the required frequency gets through. I need to eliminate all other spurious IR frequencies.
I have seen a few sites that provide filter calculators, but I immediately get lost, for example, I don't know what value to use for impedence etc. Any help in determining the component values for the filter is appreciated.
Can someone please provide me with a diagram of a circuit that I can use to detect the output from an IR diode which is being switched with an underlying frequency of around 36KHz. The output from the LED will be on/off pulses, each pulse having a period of say, 200ms. When the LED is 'on' it will be sending IR out at a frequency of about 36KHz.
What I need to do is detect when the beam from the diode is interrupted.
I've been trying to do something similar using a specialised IR receiver chip (ZD-1952) but without success. I thought that going back to basics, using an IR phototransistor, some kind of amplifying circuit, and a filter should let me detect the square wave that I will be emitting from the diode. Once I have the waveform reconstructed in the receiver, I can then use the 555 'missing pulse' circuit to detect when the beam (pulse train) is broken.
However, the part I don't really understand is how to filter the signal being received by the IR photo transistor, so that only the required frequency gets through. I need to eliminate all other spurious IR frequencies.
I have seen a few sites that provide filter calculators, but I immediately get lost, for example, I don't know what value to use for impedence etc. Any help in determining the component values for the filter is appreciated.