IR protocol #4
Description
From Edward: Regarding the bandwidth, i am thinking about having multiple level's of PWM ratio to have more bits into one HI/LOW cycle, i.e. 10% Hi 90% Low = 0, 20/80=1, 30/70=2, ... 90/10 = 8, essentially I could have 1 byte per Hi/Low cycle.
Datasheet of various 39K receiver units recommend a minimum 6~10 38k pulses for a single HIGH signal, which means with the scheme listed above, each Hi/Low cycle would last about 2.63ms, which gives us 380byte/second.
Another choice we have is to modulate a low braudrate UART signal directly over the 38K signal, the main reason i didn't make this the first choice is almost all infrared control signal uses PWM instead of UART, and with UART, there is a possibility that a long chain of 0s transmitted would result in wrong interpretation on the receiver side. Also, PWM scheme allows us to use some dumb circuit to generate a fixed pwm signal as beacon.
Experiments needs to be conducted to determine exactly how many bits can be put in one cycle before it starts to become unreliable.