IR Matrix

This robot has a square matrix of IR sensors pointing to the ground which gives the ability to detect complex patterns on the floor.

How it's built

Since it's a 7 by 7 square matrix it becomes unfeasible to connect every single IR sensor to an ADC input pin, thus a multiplexer was used to alternate between each row. This means that data is read in parallel row by row by setting the multiplexer's select pins.

Electrical configuration

This configuration not only decreases MCU pin count usage but also greatly reduces power since each row it's connected to a single 12V power rail in series. Special attention has been given to the size of the resistor in series with each row, and because there is a transistor at the end of the rail to be able to switch off the sensors when not needed this introduced another resistance in series so both had to be taken into account.

Resistor sizing