IR proximity sensor

[varuntejavarma]

Hello,

I want to design a Low cost IR proximity sensor. I have tried a normal circuit from internet and achieved a range of about 3- 4 cms. I want to acheive a range of about 1.5 metres. so I have decided to pulse the signal at a particular frequency.

I have decided to pulse the signal at 56khz. I would do this at the transmitter side using a pic mcu. But at the receiver side i have tried using a tsop4856 Ir sensor. But i would like to design a circuit of my own using a normal Ir photodiode or Photoresistor. I checked the tsop sensor datasheet and found that it uses a bandpass filter and an amplifier to allow and amplify only 56 khz signals. I am not sure about the calculations and design of a circuit at receiver end to acheive my task.

I have attached a circuit diagram which i found in internet with 10khz band pass. I dont know if this is correct . If so, which values should i change to get a bandpass at 56khz and why. It would be very helpfull if someone could explain the circuit as well.
I am a beginner in this field and technically this is my first project on my own. I want to learn by doing.Any kind of help would be appreciated.

Regards and Thanks

[pebe]

The circuit you show is of a bandpass amp,U2B, followed by a detector, D2, then U1B used as a level detector. It should be OK if you change the feedback values of U2B.

This link will give details of component values. Your filter is shown about half-way down the page.
http://www.electronics-tutorials.ws/fil ... ter_7.html