USB to TTL cable

[billyzelsnack]

I'm thinking of buying a USB to TTL cable to interface directly with the Dynamixels. This cable + a uC to handle direction should allow me to go at full 1M baud.

http://apple.clickandbuild.com/cnb/shop ... :+TTL-232R

My question is will I need the 3.3V or the 5V version?

Also, anyone know of a place where I can get one of these in the USA or better yet.. Give me a hint to when the USB2Dynamixel is going to come out so I can buy that instead?

[billyzelsnack]

Cool. Looks like I can get it at mouser for $20. I could go ahead and get some connectors while I am at it.

http://www.mouser.com/search/refine.asp ... L-232R-3V3

[JonHylands]

That will not allow you to talk to AX-12's directly, or DX-series servos either for that matter.

You need a microcontroller in the middle. The USB2Dynamixel shown on the Robotis site has some electronics inside the shroud.

- Jon

[billyzelsnack]

I was thinking about this last night, but why do you need a uC at all? Is there any reason why you could not control the small circuit in the ax-12 docs with the RS232 control flags? Tie RTS or CTS to that circuit and always set it when you want to transmit. Set it opposite once you are done transmitting and wait until you get the expected reply before you transmit again.

[JonHylands]

The problem is one of timing. You would need a bus switch to do that, and then you would need to be able to switch the Tx pin off and the Rx pin on within a hundred microseconds of being finished transmitting. Since the UART is being done on a USB chip, you really have no idea when it is done sending characters, at least not on a micro-second level.

- Jon

[billyzelsnack]

I guess the only way it would work was if you could do your transmits and then set your control flag and can count on that control flag only setting once that data is done transmitting. Hey.. Maybe it does do that by design? It sure would be nice if it did. Guess I need to go look at some RS232 specs.

[billyzelsnack]

I just realized that I have TINI devkit laying around. I could use it to setup a ethernet to rs-485 connection. Maybe I'll try that tonight.

[billyzelsnack]

Wait a minute.. The AX-12 is not actually 485. Only the fancier servos are. Scratch that idea.

[JonHylands]

Yeah, the AX-12 is TTL-level half-duplex RS-232 on a single wire.

The DX series uses standard RS-485 comms...

- Jon