Adding Bluetooth to Vex

[CyberTroniX]

Originally Posted by Joe Johnson

#5 You will have to modify the VEX default code to get messages from the serial port rather than from the Rx radios. Not too complicated I would guess because the VEX machines are supposed to be easily used in autonomous mode. This would look just like an automonomous mode only with information coming in from the serial port.

Good luck.

Joe J.

Why use the serial input although i can use Rx1 ??

[foobert]

Originally Posted by CyberTroniX

Why use the serial input although i can use Rx1 ??

ok. i have been confused.

my controller is still sandwiched in the middle of my squarebot so i was unable to actually look at it and see the labels on anything. i was under the impression that you were referring to the i/o pins labelled rx and tx on the top side of the controller. connect your blue tooth module to them.

rx1 and rx2 on the back, (?), side of the controller are not serial ports. they are for connecting the vex radio receivers. they wouldn't know an rs232 protocol if it jumped up and bit them on the... well, you know. they expect six channels of pwm data which your bluetooth module will be unlikely to produce.

sorry for the confusion.

mea culpa.

[BrianBSL]

Originally Posted by foobert

ok. i have been confused.

my controller is still sandwiched in the middle of my squarebot so i was unable to actually look at it and see the labels on anything. i was under the impression that you were referring to the i/o pins labelled rx and tx on the top side of the controller. connect your blue tooth module to them.

rx1 and rx2 on the back, (?), side of the controller are not serial ports. they are for connecting the vex radio receivers. they wouldn't know an rs232 protocol if it jumped up and bit them on the... well, you know. they expect six channels of pwm data which your bluetooth module will be unlikely to produce.

sorry for the confusion.

mea culpa.

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.

[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.

[CJO]

The easiest way to do it would be to use the "programming" port on the vex as opposed to the radio port.

[Joe Johnson]

Originally Posted by CJO

The easiest way to do it would be to use the "programming" port on the vex as opposed to the radio port.

Does the programming port on the VEX use RS-232 voltage levels (<-5V = 1, >5V = 0) or TTL voltage levels (<1.4V = 1, >1.4V=0)?

Sorry for the silly question. I am out of the loop on VEX stuff.

If the Programming Port uses RS-232 voltages, then you could use an off the shelf Blue Tooth radio like this one.

Otherwise, I would use the TTL voltage level serial port and use one of the modules that is compatible with that voltage level.

Joe J.

[foobert]

Originally Posted by Joe Johnson

Does the programming port on the VEX use RS-232 voltage levels (<-5V = 1, >5V = 0) or TTL voltage levels (<1.4V = 1, >1.4V=0)?

programming port is ttl. programming dongle, however, has level shifter in it and since you need one anyway to program the controller to listen to the serial port, there's no point in not using it with an rs-232 level radio if that's what you've got. otherwise a ttl level radio could be used on either the programming port or the rx and tx connectors up top.

[Joe Johnson]

Originally Posted by foobert

programming port is ttl. programming dongle, however, has level shifter in it and since you need one anyway to program the controller to listen to the serial port, there's no point in not using it with an rs-232 level radio if that's what you've got. otherwise a ttl level radio could be used on either the programming port or the rx and tx connectors up top.

This Radio, by AirCables, is an RS-232 radio that have used a lot and that I love. It has only 10M range, but it is beautiful in terms of its performance. I have not done it myself, but the engineer at AirCables tells me that if you crack the case it has the ttl signals easily available on pins. Highly recommended.

Joe J.

[AJBelayer]

Ok I am new to the vex world but I have been in programing (C, C++, java, assembler, etc.) for a while now and I want to add bluetooth to my vex robot for control, I assume this is done easiest over the serial port connection and i have rad this entire thread. Has anyone successful done this? If so would you be willing to help me get figured out where to start and what radios work best? I would like to stay with the 100m range bluetooth.

AJBelayer

[rswsmay]

I can't really speak to whether this is entirely "doable", however you should post this question on the vexlabs.com forums.

[Joe Johnson]

As I have said before, I am really happy with AirCables, and recommend that you try to use one of there products.

If you want 100m range, you are going to have to go with something with an antenna. The AirCables parts with antennas are listed as "coming soon" But, I would call or e-mail Juergen at AirCables. I think they are shipping some of these 100m products but have not updated their website.

The PC side is pretty straightfoward. The USB dongle from AirCables is only a Class 2 (10m) device but there are many, many, many "Class 1" (100m) Bluetooth USB Dongles available that you can use to make your connection to the robot. I have never used any of them so I can't help you with a specific recommendation. But, I have used many of the 10m devices and they basically all work okay. The only difference between them is whether they use the standard WindowsXP BT driver or whether they have written their own. I had pretty good success with a Linksys 10m dongle as well as the AirCable 10m dongel part for what it is worth. As to the programming, once the device is installed and the BT radios have been paired and connected, the BT driver provides transparent virtual COM port.

Hope this helps.

Joe J.

P.S. I take back many of the good things I said about the SMART Modular Bluetooth Serial Adapter above -- I can't speak for other applications, but for mine, they ended up being the source of subtle problems that were very hard to find but caused me fits for MONTHS. Your mileage may vary... JJ

[Joe Johnson]

I just came across this product from the guys at SparkFun.com

Shown here:

Anyway, the purpose of this thing is to provide an easy way to do level shifting between RS-232 <->TTL voltages.

If you want to use an RS-232 voltage level device with the TTL level pins of the Vex controller, this thing could come in handy.

FYI.

Joe J.