Reflective IR wall sensors: design and test

Tony Wilcox of Birmingham City University has been working with the design and implementation of Infra Red wall sensors for their student micromouse design. This type of sensor has become common in mouse designs although there are several variations on the theme. Tony’s version uses readily available parts in a robust and repeatable design with a couple of extra tweaks that make it possible to use the same sensor to measure distance over a very wide range of distances without having to change the drive current to the emitter…

The key to making these sensors able to work over a range of distances lies in the behaviour of the detector immediately after the pulse. The rise time of the detected light is dependant upon distance. That is, with a very bright pulse, corresponding to a close object, the signal from the detector rises more quickly than it would with a less bright pulse. Normally, the processor would simply measure the steady-state value of the detected light after some fixed time period. Here a measurement is made while the received signal is still rising. By carefully timing the instant at which that reading is taken, the sensor can respond to a much greater range of distances.

For full details of the sensor including the schematics, response curves and software implementation, have a look at Tony’s powerpoint presentation:

IR Sensor Design – Tony Wilcox