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Originally Posted by JBotAlan
After reading over the CMUcam documentation, I see that the camera board has a TTL port. I remembered this from the RC, so I read the docs for it, and sure enough, we have a TTL port there. So, I have to know, why do we use a TTL to RS-232 converter? Is it a matter of convenience (3 wires to run instead of four)?
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2 notes:
1) When the camera first appeared in 2005, I wanted to use the TTL capability of the camera. Unfortunately, when I inspected the camera back then, it appeared that the jumper on the original CMUcam2 design which allowed you to switch from RS232 levels to TTL was omitted, making it impossible to use the TTL port. I didn't check to see if this was fixed on the 2006 version of the camera but I don't believe it was.
2) A good reason to use RS232 levels over TTL is noise immunity. Using RS232 levels will give you better noise immunity which could be important when running with all those noisy motors all over a robot. That being said, we've used TTL serial for things on our robot in the past and have never had a problem.
Also, regardless of which method you use, you only need 3 wires. The fourth wire on the TTL serial port is +5v which doesn't need to be connected (assuming your camera is already getting power from the PWM port).