It looks like a lot of the VEX Transmitter/Receiver add-on kits have been dumped on the market. They normally sell for around $129, but have been showing up on eBay for $20 plus shipping.
The transmitter looks like a normal R/C transmitter, but the receiver has what VEX claims is an RJ-10 jack that provides a connection from the receiver to their microcontroller.
Has anyone here ever hacked one of the VEX R/C receivers? VEX claims that the receiver to microcontroller interface is proprietary and will not release any information about it.
I suspect that VEX is sending PWM signals over the inteface and the microcontroller is decoding the pulse length like a servo does and is controlling the attached motors and servos accordingly.
A quick search on Google did not reveal any source of information on the interface. Can anyone here point me to a possible source of information on the receiver to microcontroller interface? Otherwise I will have to round up an oscilloscope, which I presently do not have, to look at the reciever output.
For anyone interested in using the VEX R/C Transmitter & Receiver add- on kit due to the low price it is selling at now on eBay and elsewhere, here is a link to an article describing the receiver electrical interface and how to decode it: allelectronics.com/spec/JS-6.pdf
I’m decoding the Vex with a BX-24 sucessfully (and easily with InputCapture), but every center-channel on both transmitters I have is ~1.125mS, not the standard 1.5mS. I’ve searched thoroughly, I think, and find nothing to suggest that the Vex timing should be anything but standard R/C 1.0-to-2.0mS pulses.
I’m wondering if the discounted transmitters on eBay and elsewhere are the result of a bad batch. Do others who have purchased these discounted Vex transmitters see non-standard modulation timing?
I believe that the VEX R/C combos for sale on eBay are the same units for sale at All Electronics where the JS-6.pdf file is located.
The VEX receiver serial output analysis in the JS-6 document seems to indicate that the channel center is located around 1.5 ms which includes the 400us servo framing pulse .
Since you are getting around 1.125 ms for you channel center, I do not think that your program is adding in the 400us servo framing pulse which will give you around 1.5ms.
You are quite right. I misunderstood the Vex pulse stream (despite having that PDF on the bench, sadly). Timing between rising edges makes perfect sense. Thanks.
