The synchronization frame is six short pulses and six long pauses followed one extra-long pulse and one extra-long pause. The signal appears to consist of a synchronization frame followed by a payload. HC361 PWM output probed with an oscilloscope The short pulses and pauses are about 210 us long, and the long pulses and pauses are about 420 us long. If you look at where the signal goes high, you can see it ripple at (I assume) 315 MHz as the transmitter draws power from the battery and causes the system voltage to droop. There are short and long pulses and short and long pauses. I probed the PWM output of it and found that it outputs a PWM signal (duh). I did some digging and found out that the "rolling code generator IC" is a Microchip HCS361 (even though it's labeled as HC361 in the schematic.). In the picture below, I labeled the interesting bits of the circuit: the "rolling code generator IC" (a Microchip HCS361), the 315 MHz SAW resonator, 94430-T44 RF transistor, a trace used as an inductor, and the trace used as an antenna. Here's the schematic from the FCC website:Īnd here's what the key fob circuit actually looks like: By looking at these I was able to figure out, generally speaking, how my key fob works. The FCC entry for KOBLEAR1XT has a schematic, a block diagram, and even internal photos of this device. The FCC ID of my key fobs is written on the back of the case: "KOBLEAR1XT". My key fobs are registered with the FCC (as most electronic equipment is), so I was able to look them up by their FCC ID to get a lot of information on them.
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