IR reflex

Posted on Feb 6, 2014

The vehicle acts in any way at this point electronically - for example, by its metal (change frequency of an oscillator) or by its components (eg RFID) Depending on the method used different grades of security and error tolerance can be acheived. Even recognition of individual car types is possible. Example: with the help of a light barrier (direct light) and the characteristic patterns

IR reflex
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when a train moves by it is possible to automatically separate passenger trains and freight trains. A barcode could be read as well as an RFID chip. A relatively inexpensive method for detection are reflective light barriers. These are mounted in the center of the rails and detect the reflection by a train passing by. The diode should be operated with a current of 20mA at a voltage drop V(forward) of 1. 3V. The resistor calculates 180 ©. According to the data sheet of the CNY70 the collector current at the output with an object in 10mm distance is approximately 50 µA. Thus, with 47k © pullup resistor a reasonable voltage (0 to 2. 5V) at the input of the attiny will result. The pullup is connected to an auxiliary voltage of 2. 5V. The photo transistor will not only be activated by the reflected light, but by the overall ambient light as well. To ensure reliable detection, the influences of the ambient light (eg, 50Hz hum from the room light) must be eliminated. This can be achieved by an accordingly protected installation and on the other hand by appropriate filtering. This is done by sending a certain code to the emitting diode and checking at the recipient, whether the fluctuation of the measured light intensity matches this code. Here a very simple code`01010` is used. The symmetry in the code smoothens slow fluctuations. The measurement is performed with the integrated ADC of the ATtiny26. This converter requires 13...

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