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.

[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.

[AJBelayer]

Ok so I am looking at this Bluetooth device for me they are a local company so I can pick up the device and not have to worry about any shipping time. As I understand it i connect the Tx and Rx to the Tx and RX on the vex controller but then where do I connect the pwr and ground? An independent power source or is there 3V-6V power on the vex. Also I still have to check with the manufacter to make sure this is putting out TTL signal and not RS232 correct?

P.S. the link for the site of the bluetooth chip is here http://www.sparkfun.com/shop/index.p...rds=Bluetooth&

[Joe Johnson]

Originally Posted by AJBelayer

... As I understand it i connect the Tx and Rx to the Tx and RX on the vex controller but then where do I connect the pwr and ground? An independent power source or is there 3V-6V power on the vex. Also I still have to check with the manufacter to make sure this is putting out TTL signal and not RS232 correct?

As to the TTL question, this is from the datasheet

Note: All pins are VDD tolerant. This means that the BlueSMiRF can interface to 5V logic, 3.3V logic, and even 6.82V logic. Onboard MOSFETs translate the onboard 3.3V to whatever voltage you power the unit to. If you power the unit with 5V, the unit will output 5V for a logic high, OV for a logic low, and can tolerate logic high levels into the input pins up to +5V.

As to the power question, I suppose you can steal power and ground from a PWM output. I have not put a meter to the power but I think it just passes power from the battery. Now that I think about it this may cause you problems.

The problem is that the Vex battery fully charged could be as high as 8V or so. From the datasheet, the input voltage would be okay (under 10V is the spec I see) but the problem is that :

1. On data TO the radio: I am not sure that the Vex TTL logic level 1 output would be read as a 1 by the radio input (read above)
2. On data FROM the radio: I am not 100% sure that the Vex TTL logic level input will like have 8V as an input

I would GUESS that it is okay, but I wouldn't want to bet my Vex controller on it.

I recommend buying a 7805 5V regulator and knocking the PWM power output down to 5V.

Good Luck.

Joe J.

[foobert]

Originally Posted by AJBelayer

As I understand it i connect the Tx and Rx to the Tx and RX on the vex controller but then where do I connect the pwr and ground?

the rx and tx connections on the top of the vex controller each have 5v and ground available on the connector next to them. so connect rx-i on your bluetooth module to the pin next to the label on the rx connector, connect tx-0 on the bluetooth module to the pin next to the label on the tx connector, connect ground to the pin opposite the label on either rx or tx, and pwr to the middle pin on either rx or tx. when you get around to programming you'll be using usart2 rather than usart1 which is the programming port with the rj-12 connector on the back of the unit.

[Vex13]

I'm pretty new to all this and wanted to just confirm a couple points, if someone would be so kind... Thanks in advance for your time and help!

1) With the programming dongle, any rs232 bluetooth device should work fine since it has a level shifter built in. Is that a correct statement?

2) Is there power provided on pin 9. I.e. for the devices mentioned (the aircable card http://www.aircables.net/serial.html, and the smart bluetooth module http://zbausa.com/bluetooth_serial_port_adapter.asp)? If not, what would be the easiest way to provide power to these devices? Preferably it would come from the vex module, but an easy external source would be fine too.

3) If you already have the desired behavior occuring between the pc and micro via a thethered link, add a bluetooth link between the pc and programming dongle should be pretty much plug and play (add the module and pc dongle, set up the link, adn we're set). Right? Or am I being too naive here?

4) If the power isn't provided for the aircard cable that Joe is recommending (which would currently be my first choice), do you forsee any problems with the following device, which has an internal battery: http://www.lemosint.com/scripts/blue...gle_class2.asp

Thanks again for taking the time to help where you can. It is greatly appreciated!