“I am trying to use IR sensors to detect where someone is sitting in a room. The IR sensor would be placed on a rotating panel where it will send signals to the microprocessor about where it detects people sitting and the microprocessor can then plot in the 360 circle at which angles it received the input.
For this, what do you suggest is the best way to go? I was thinking more about getting IR body heat sensors premade components (~$6-$10) which give out high or low processed signals when they detect heat and sending it off to an arduino board. But it looks a bit on the expensive side. Is there anyway of creating this setup cheap?
What a fun question!
I spent the past couple of days coming up with what I think would be viable solution to your problem. To start, Adafruit happens to offer a great little PIR that, as you suggested, responds with a high/low signal in correlation to a IR source crossing its path. Adafruit’s PIR also has a 120 degree viewing angle, which is a bit wide if you are trying to pinpoint a person in a room. Because the device relies on the “path” state to change between the two sides of the sensor and you want to pinpoint a heat source, you will have modify the sensor to limit the viewing angle. You can do this by removing the faceted Fresnel lens and attaching a small tube about 1″ long over the sensor or by covering a percentage of it with some non-transparent tape (this certainly would require some experimentation). Ladyada has a wicked tutorial about PIRs work and how to modify/use it.
The next problem is the fact that you want to view in 360 degrees. I came up with three solutions for this. First, which is the most costly, would be to make your circuitry wireless, relaying the data back to a server. This also poses the problem of powering the device. The second would be to keep the sensor tethered and sweep the device clockwise then counter clockwise. Finally, the third, would be to follow the attached diagram. I had the idea that if you used an 1/8″ stereo “headphone” plug & jack you could simulate a slip-ring (commonly found in wind turbines to transfer electrical energy from the generator in the rotating nacelle). This would allow you to isolate the PIR on a rotating platform and transfer signal/power to the device without interruption. You might want to add a little non-conducting grease to the interface to keep it from wearing out.
In order to make the device rotate, I would recommend using a stepper motor attached to a larger gear, which acts as a yaw bearing for the PIR platform. You can easily control the stepper using an H-bridge (for bipolar) or darlington array (for unipolar) to precisely cover your 360 degrees. Now you get to do the math to determine how many steps per rotation, decoding the PIR, etc.
I hope this answers your question! Up next is J.Miraldi with a question about creating a robotics program for their high school!
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