OpenServo.com

ahoeben · Joined: 20 Jun 2008 Posts: 20

I'm considering using a 3.3v microcontroller to control my openservos.

Given that the openservo boards (V3) are powered with 6V+ (and a regulator on-board to get that down to a stable 5V), would it work if I used 3.3V signals for SDC and SDA, or would I really need to levelshift these lines?

Cliff · Joined: 23 Jan 2007 Posts: 150 Location: Saratoga, CA

Hi ahoeben,

It depends on the specifications of the microprocessor you are using - if it has 5V tolerant I/O (for Reset and INTn signals), it will work without level shifting. However, you will have better noise margin if you level shift.

The SCK and SDA signals are open drain (no pull-ups on OS board), so they can be pulled-up to 3.3V, but pull-ups to 5V will give better noise margin.

Cliff

ahoeben · Joined: 20 Jun 2008 Posts: 20

Thanks for your response. I'll be using an Arduino Pro Mini 3.3v:
http://www.arduino.cc/en/Main/ArduinoBoardProMini

Why would I need 5v tolerance onthe reset line of my mc? It is not connected to the i2c port, is it?

Cliff · Joined: 23 Jan 2007 Posts: 150 Location: Saratoga, CA

ahoeben,

The reset line is brought out on the OS connector and can be used to get one or more OS's into a known state without power cycling (e.g. in the case of mind loss after a brown-out). The reset line is pulled-up (10K) to 5V on the OS board.

Cliff

ahoeben · Joined: 20 Jun 2008 Posts: 20

Ah, right. Thanks for the explanation. I'm not connecting the reset-line, so I guess I'm not going to blow up my os boards by talking to them with 3.3v (apart from possibly increased noise issues).