Adding Bluetooth to Vex

[foobert]

Originally Posted by BrianBSL

I wouldn't say they aren't serial - they are somehow modulated as there are only 4 conductors there and you have 6 chans of PWM there, so something has to happen to squeeze that onto 4 pins. I would guess, however, that it isn't RS232 but rather some proprietary protocol. If you knew the protocol that was sent there you could use another PIC to convert RS232 to that protocol, but that would be pretty pointless and a lot more work, unless you didn't want to spend $100 on a Vex programming kit and already had a PIC programmer.

I think what foobert is referring to are the TX/RX TTL pins on the same header as the Analog In/Digital IO ports. Note that to do full RS232 you likely need a level converter as well, as I'm pretty sure they are only TTL level.

ok, last things first. the bluetooth modules these guys are considering are ttl, so no level converter is required.

that was pretty easy, so on to the first thing. the inputs to rx1 and rx2 are ppm which is a sort of multiplexed pwm signal.

the way i understand it is this. for the six channels on the vex radio, you get seven short pulses. the time from the beginning of the first pulse to the beginning of the second pulse is the duty cycle for the 1st channel pwm, the time from the beginning of the second pulse to the beginning of the third pulse is the duty cycle for the 2nd channel pwm, etc.

so the data for the six channels take anywhere from 6 to 12 ms depending on the sum of their duty cycles. these are followed by the seventh pulse and a lengthy pause of say six to twelve ms before the next data frame is sent. the long pause allows the receiver to synchronize the data frames.

hope that makes sense.