IR proximity sensor

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

Hopefully you know what D1 R10 does. Light to voltage.
C8, R8 blocks DC. Passes high frequencies. This should remove room light and pass the 56khz.
R5,R2,C6,C5 makes a filter that is not set to 8khz. (not 10khz)
D2,C7,R7 is a peak detector that will capture the strongest signal.
U2A compares the signal to a set level. Set level = R3.


If now we have a 8khz filter and we want a 56k filter then we need 7x faster. So lets reduce C5,6 and 8 to 140pf.
Here is the frequency response of the new filter. At the left side is 60hz where light bulbs add noise. The gain peaks at 55khz.

Hope that helps.

varuntejavarma, It is important to note here that this is a professionally designed circuit and since this is your first project, you might not be about to differentiate between different small sub-circuits used in this schematic. Resisters and capacitors are used together to make high-pass filters and using an op-amp in this feedback configuration basically makes it a peak detector. Anyways, with the correct values of resistors and capacitors, you’ll be able to make this circuit work.

complete pcb