Touch Sensors

The project uses both touch sensors and infrared reflective light sensors.

The touch sensors are Fischertechnic microswitches, which fit easily onto the chassis members. One is fitted near the rear, as a pushbutton for the operator, and another is fitted to the front to simulate a collision detector.

Infra-Red Sensors

The infra-red sensors are home made, and about as simple as such things get. Each has an infra-red LED for illumination and an infra-red phototransistor as a detector. The LED has a current limiting resistor and connects to a Picaxe output. The phototransistor connects to a Picaxe digital input, and relies on the project board's pull-down resistor to complete its circuit.

In use, the sensors are 1cm or so away from the track. The phototransistor appears "off" to the controller when it is over the black track and "on" when it is over the white background. There is some sensitivity to ambient light but, in use, they are fitted on the underside of the chassis which provides sufficient shadow.

Three of the IR sensors are generally used: two for detecting the track and one for detecting the trackside markers. We supply them hot-glued to Fischertechnic bricks, for easy mounting on the chassis.