Direct TTL to RS232 connection

[JaysonJT offline]

Hello everyone,

Early New Year's greetings to all - 2012 should be an exciting year

I have 2 Questions - if anyone would be kind enough to help me out with this, I'd be extremely grateful

Question 1:
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I've ordered the following TTL-to-RS232 converter board:
( http://www.virtualvillage.co.uk/max232- ... 2-008.html )

- If I connected the RX & TX pins (on the converter board) to each other & took a single wire from the combination of the 2 & link it to the data line of the 3 pin/half-duplex ttl connector on the havimo board - would my PC be able to properly recognize the RS232 link & talk to the camera via the GUI for calibration?

Question 2:
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I'm going to be powering the 2 boards via a power supply

1. How much voltage/current would I have to supply - I was thinking to go for 5V & 3.6mA, since the Atmega8 chip has been specified to work normally at that rating. Is this right?

Unfortunately, I don't have the money to buy a USB2Dynamixel adapter since I've spent most of my budget on a Kondo robot + roboard + sensors + havimo. So now I'm having to try & figure out a low cost way of connecting to Havimo.

Many thanks
Jayson

[i-Bot offline]

I am sure you will get a better answer from Hamid, but:

Question 1: An RS232 to TTL converter based on MAX232 will not work on the Dynamixel bus. The Dynamixel bus is a bidirectional bus and depends on the ability of the drivers to not drive the bus when they are not transmitting. The MAX232 drives the bus all the time. FTDI USB serial ICs provide a /TXEN pin which is usually used to enable an external tristate TTL driver. Where are you located, there may be someone local who can help if you just want to get calibrated.
Is there no way to use the Dynamixel interface on your Roboard ?
Also not sure if Robobuilder mode is possible, since this has separate TX and RX.
Question 2: The MAX232 board would need a 5V supply, but the Havimo needs a higher supply (7.5 to 12V). This is likely due to an internal regulator to 5V . You should supply with 7.5 to 12V and the supply current would probably be higher for the complete camera., I guess at least 500mA

[JaysonJT offline]

Whoa! 500mA is a lot

Yeah, I'll try using the robobuilder mode for the calibration.

I'll be using the ttl interface on the Roboard to communicate with Havimo towards the end - I'm going to try & compile a minimal Linux OS for the roboard - so I won't be able to run the Calibration GUI on it.

Thanks for your help i-Bot.

[hamid_m offline]

Hi Jayson, I-Bot,

The module sinks less than 100 mA. But the supply voltage should be more than 7.5v.

Connecting Tx and RX may work but would be a little bit tricky, as you may:
- avoid conflicts (wait until a reply packet finishes before the next command is sent)
- be prepared also to receive what you send as command on your RX line.

You don't need to use the calibration program on board. Calibration is usually done off line.

Best regards,
Hamid.