OpenServo.com Forum Index OpenServo.com
Discussion of the OpenServo project
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

3.3 volt compatibility

 
Post new topic   Reply to topic    OpenServo.com Forum Index -> Hardware
View previous topic :: View next topic  
Author Message
ahoeben



Joined: 20 Jun 2008
Posts: 20

PostPosted: Sat Mar 26, 2011 2:09 pm    Post subject: 3.3 volt compatibility Reply with quote

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?
Back to top
View user's profile Send private message
Cliff



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

PostPosted: Sun Mar 27, 2011 2:38 am    Post subject: Reply with quote

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
Back to top
View user's profile Send private message
ahoeben



Joined: 20 Jun 2008
Posts: 20

PostPosted: Sun Mar 27, 2011 7:39 pm    Post subject: Reply with quote

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?
Back to top
View user's profile Send private message
Cliff



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

PostPosted: Sun Mar 27, 2011 10:17 pm    Post subject: Reply with quote

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
Back to top
View user's profile Send private message
ahoeben



Joined: 20 Jun 2008
Posts: 20

PostPosted: Mon Mar 28, 2011 12:12 pm    Post subject: Reply with quote

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).
Back to top
View user's profile Send private message
servet



Joined: 24 Jun 2013
Posts: 1

PostPosted: Mon Jun 24, 2013 5:41 pm    Post subject: Reply with quote

You need to use the level shifters or use a 555timer in monostable mode to decrease load from your controller in case youíre using a lot of servos. The servos are mechanical parts and since I donít know the exact specification of your servos, Iím going to assume that they require a lot of current for operation like normal servos, when you try to make them operate at a lower voltage, they draw more current, hence endangering your controller circuitry. So to be on the safer side, always use a level translator or an external buffer.
_________________
turn-key circuit assembly
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    OpenServo.com Forum Index -> Hardware All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group