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IR distance sensor design

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Someone Electro

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I am designing a simple IR distance sensor for a robot. Its main job is to estimate how the walls around the robot are. It runs trough a maze so it needs to look left and right and also forwards. The left and right sensors will need to work for aprox 4 to 15 cm while the front sensor will need to see up to 30 or 40 cm.

The circuit i made blinks a LED at about 500Hz and then measures the bounced back signal. Because i will need 3 of these i try to keep component count down and use only 1 opamp per sensor. The circuit is basically a very high gain active high pass filter that has a 0,6V virtual ground (to compensate for the drop on the output rectifier) Also i found out that i needed to put a filter on the phototransistor circuit as it was slightly picking up the 500Hz signal off the power rails.

So i want to know if my circuit has any design flaws that might become problematic and suggestions how to improve on the linearity and such. I designed this from scratch so i guess some of you analog guys have flaws to point out.

EDIT: The opamp is MCP6002
 

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Someone Electro

New Member
Oh sorry that's MCP6002. Its a rail to rail 1Mhz low power opamp. Dont think this circuit would need a special high performance opamp.
 

audioguru

Well-Known Member
Most Helpful Member
The opamp is a noisy one and you have it operating with no negative feedback at high frequencies. A low noise opamp with a resistor in series with C2 to ground would work better.
 

Someone Electro

New Member
There was a resistor there originally but without it it seams totally immune to 50 and 100Hz light sources (Room lighting) while still working fine for that 500Hz signal. Or it could be that the breadboards capacitance is making this work

Oh and i didn't find the op amps noise to be a problem since with a 10M feedback it could measure up to 100cm without noise being a problem (Also this is tested on a breadboard so lots of noise and capacitance there)
 

momo26

New Member
hello,
i've tried to implement this circuit this morning for a project but it doesn't work for me
someone has tried it ?? it works??
thkx:)
 
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