boylesg
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Assuming I am OK with setting up a 555 bases PWM (53kHz) to run a few IR LEDs and that I can get an unmodulated IR LED and phototransistor to drive a red LED as an indicator as you pass your hand over the phototransistor.
What is the best way to go about demodulating a 50kHz IR signal coming from the phototransistor.
I have tried a high pass filter with a 4 x 1n5891 rectifier and a smoothing capacitor to convert the signal back to an analog voltage level but the high pass filter seems to reduce the voltage level down to millivolts.
I have tried a class A amplifier with a min frequency of 30kHz, but the 50kHz signal can't seem to pass the 220pF coupling capacitors that 'Transistor Amp' (class A amplifier design software) computes. I specified 50k for both input and output impedance - I suppose I am not specifying the correct impedance for the 50kHz signal.
Does any one know of a good website that explains in detail how to do this sort of thing?
Some else on another website has suggested a bandpass filter. Although I understand what one is and how in theory to arrange one on a breadboard, I need specific worked examples with a square wave in order to gain a decent understanding. I have found numerous examples but not this sort of specific application.
Can anyone point me in the direction of a good web page?
What is the best way to go about demodulating a 50kHz IR signal coming from the phototransistor.
I have tried a high pass filter with a 4 x 1n5891 rectifier and a smoothing capacitor to convert the signal back to an analog voltage level but the high pass filter seems to reduce the voltage level down to millivolts.
I have tried a class A amplifier with a min frequency of 30kHz, but the 50kHz signal can't seem to pass the 220pF coupling capacitors that 'Transistor Amp' (class A amplifier design software) computes. I specified 50k for both input and output impedance - I suppose I am not specifying the correct impedance for the 50kHz signal.
Does any one know of a good website that explains in detail how to do this sort of thing?
Some else on another website has suggested a bandpass filter. Although I understand what one is and how in theory to arrange one on a breadboard, I need specific worked examples with a square wave in order to gain a decent understanding. I have found numerous examples but not this sort of specific application.
Can anyone point me in the direction of a good web page?
