I2C Interface & Voltage Help


4 posts
by crsskynet » Sat Oct 20, 2012 9:04 pm
Dear fellow Raspberry Pi users & experts,

I'm in need of some advise. I'm about to start building my first ever Raspberry Pi project and what i'm wanting to do is use the Pi as the brain and then using I2C Interface Bus to control everything and get the sensor inputs back.

However i'm a little worried about all the messages and info all over the www that I read regarding 3.3v and 5v circuits for I2C equipment and the Pi itself.

So I'm wondering can anyone give me an answer to the following;

The modules I intend to use are as follows;
http://www.byvac.com/bv3/index.php?route=product/product&product_id=79 as my main A to D / D to A and startup relay controller

http://www.byvac.com/bv3/index.php?route=product/product&product_id=103 to give me 8 more relays.

and finally as a way of displaying some nice outputs from my program this LCD display http://www.byvac.com/bv3/index.php?route=product/product&product_id=59 using the I2C Controller http://www.byvac.com/bv3/index.php?route=product/product&filter_name=BV4618&product_id=100 which convinently also give me my inputs from a keypad.

Now just about all of these boards use 5V to power them, in fact the page about the BV4618 controller for my LCD display states although it can run at 3.3V most LCD's run at 5V.

So what i'm getting at is thus, if all of these boards run as I2C Slaves (because the Pi will be Master and running my programs) and they run on 5V power supplys. -----

Will I blow up my Pi if I connect it to the I2C bus of the above???

Or will it work?

Or do I need some kind of level thingy (sorry i'm new to this so dont know the correct term)??



Help Much Appreciated! Dont want to turn my first project into a very expensive pile of scrap metal.

Thanks,

Gareth
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by morphy_richards » Sun Oct 21, 2012 5:53 am
You do need a level thingy. But its not too hard, I made one using 2 MOSFETs in this thread
viewtopic.php?f=37&t=16973&start=75
See comment 4 onwards.
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by crsskynet » Sun Nov 04, 2012 11:56 pm
morphy_richards wrote:You do need a level thingy. But its not too hard, I made one using 2 MOSFETs in this thread
viewtopic.php?f=37&t=16973&start=75
See comment 4 onwards.



Thanks for the advise - just wanted to say it works a treat and the first Pi Project for my 5yr old daughter is underway.
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Location: Stirling, Scotland, UK
by pygmy_giant » Sun Nov 04, 2012 11:58 pm
I bought a ready-made level thingy because I'm too lazy to make one.
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