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Neither Baradur nor Orthanc, |
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Carrera uses the same IR hardware for their Pro X, Digital 132 and Evolution/Exklusiv lines, so what follows is valid for all those systems.
Not surprisingly there is an IR receiver and an IR transmitter inside the tower. The transmitter is build from 4 IR Leds one for each point of the compass. The IR receiver is a single device combining an IR diode or IR transistor and a frequency detector. It is set to 38 kHz. With ordinary data transmission over cable, logic values are determined by the existence of a certain voltage. When using IR transmission the logic levels are determined by the existence of an IR signal with a given frequency. In this case the existence of a 38 kHz signal with an impulse ration of 1:1 represents a logic 0 and the absense represents a logic 1.
The Blackbox starts a transmission every 75 ms by sending two zeroes. The first one is 30 pulses long and the second 20 pulses. The pause in between is 30 pulses long. As you can see in the above diagram, the receiver delays the signal and makes the low phases a bit longer than they should ideally be. The controllers will register the two zeroes and will answer. They will anser in a fixed schedule. The controller with id 0 will answer after 15 ms, the controller with id 1 after 30 ms etc. When a controller will answer depends only on it's id and is independent from the number of controllers in use.
The answer is sent using a Manchaster code, being the preferred code in Carreras system. The baudrate is about 2kb. First there is a startbit consistng of a low Phase of about 800µs and a highphase of about 750µs or 1000µs depending on the value of the first data bit. The exact times vary. A word consists of startbit and 7 data bits. The data bits are inverted. Controllerdata: SB C1 C0 T3 T2 T1 T0 SW
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