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Panopticon Towers – Adding a Side Facing Sensor

January 21, 2015

The original arduino carbot used a second ultrasonic sensor mounted low on the side of the carbot frame (circled in red in the pictures below).  Sadly, I can’t find the second sensor so i’m thinking of using the sharp IR sensor even though it seems a bit flaky.  It would simplify the code a bit because you don’t have to explicitly ping it or wait between pings – you just read an analog value.  My first thought was to mount the sensor fairly high on a bit of perfboard.  That would get it above the wiring mess, put the weight back near the rear axle, and give me a place to mount the analog to digital converter chip.  I’m rejecting that because of the number of flying wires connecting the tower to the driver board – besides power, ground and signal, I’d need four for the SPI signals and chip select.

Sharp GP2D12 sensor and MCP3002 ADC

The second approach is to mount the sensor lower, on a smaller piece of whatever attached to the header that holds the motor driver.  The ADC chip would be mounted on the driver board and only power, ground, and signal would be flown up to the sensor.  The sensor is marked out with a red ellipse in both photos and the original ultrasonic is marked with a circle.  I can’t put the IR sensor there because it has to stay at least 4″ from the wall at all times.  If it gets within 4″ it reads as if it were farther away leading to a wall-tastrophy.

15-01-21 lotower

If I’m going to solder, I’ll add a header for the bluetooth dongle at the same time if i can find room.

Update: when I actually measure it, even those locations could let the sensor get within 4″(10cm) of the wall. The sensor would have to overhang the left side of the car to be sure of staying outside of the danger zone. My only other thought is to mount the sharp sensor facing forward at the rear of the driver board and use the ultrasonic in the original position for the side facing sensor. I think maybe I’ll just order another ultrasonic and spend my energy getting the bluetooth working.

15-01-21 midtower


Update: well double-poop, the ultrasonic sensors are like $35 on digi-key.  Add tax and shipping and it’s $50.  I knew i wanted to make the infrared work!


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