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IR proximity sensor

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varuntejavarma

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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
 

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  • HaX9f.png
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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.

hax9f-png.86596

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.
upload_2014-5-31_19-26-27.png

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
 
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