Design of an IR sensor for the Fischertechnik ball track.
The sensor module has a 15mm grid, suitable for Fischertechnik and takes only 15mm extra length. The sensor is designed to work in strong ambient light without problems. It can handle fast burst mode very well. The sensor uses an IR diode TSHA6203 with a small opening of 12° to avoid being disturbed by the ambient light. The same for the phototransistor receiver SFH313FA, it also has a narrow viewing angle of 10° and has an internal IR filter. The mounting of the diode and transistor are inline built in and shielded from the environment. The light first passes through a 4mm opening on both sides. This prevents side lights from entering. The light beam is low at the surface of the ball. This allows the sensor to still look between 2 burst balls. Signal ratio is about 50% for adjacent balls. If there would be sunlight on the ball then the reflection angle is such that it cannot enter the light channel. If no ball is present, extra ambient light acts as positive feedback, i.e. the sensor gets an even better control signal.
The sensor can operate on 5V and 9V. At 5V the resistors are 390 and 820 Ohm, at 9V they are 820 and 1800 Ohm. This is shown on the pictures. The sensor is tested with the Fischertechnik TXT Controller and works perfectly, also for fast burst cycles. I use the connection of the TXT Controller 9V output as VCC and the digital inputs on 10V. The necessary current is 13.2 mA with light and 8.8mA dark. The phototransistor load at about 4.5mA.
A curve180° has also been made so that the trajectory for the balls can be quite close together. The sides of the sensor have the necessary slots to connect additional Fischertechnik blocks.