I am a beginner in field of circuits, so excuse me for my amateur questions. Let me explain my task:
I have to build a low cost proximity sensor for a sense and spray device. I have read various posts on IR proximity sensors in this site. But I am still not clear in understanding the concepts. As I am a beginner, I get stuck at some silly amateur doubts.
So, this is what I am planning to do:
Build a IR sensor transmitter by pulsing the signal to 56 kHz using the oscillator from PIC MCU and then build the receiver part by using IR photodiode, band pass filter that allows only signals with 56khz carrier frequency, amplifier, op amp as a comparator and then the output is given to the microcontroller.
When someone walks by the device, it should detect the movement and spray the liquid. after that it should go to standby mode for 15 min. It should not spray even if anyone passes at this time. After 15 min, it should come back to running mode.
This is the link for a similar type of product in the market.
My hurdles so far which I haven't crossed yet:
To reduce the effect of ambient light and other IR sources, I decided to pulse the signal. But I couldn't get the right circuit in the receiver end to demodulate and amplify the signal. Because it has to be sensitive up to 50- 75 cms (even more would be better). I can use a tsop series photodiode which comes with bpf and amplifier. But I want to build the circuit with as simple of components as possible.
When a black body is in front of sensor it absorbs all the IR radiation and does not reflect back any. I don't know how to solve this problem.
I have to design a circuit and then write a program for a PIC18F4550 microcontroller. But I think I can find a solution for the program. But the circuit diagram seems to be a bit difficult for me.
Please suggest a circuit diagram for the receiver part with the band pass filter that allows only 56khz signals, amplifier and opamp. Any kind of help and suggestions are welcome. Please don't hesitate to explain in a simple way.