Cerb40: Connecting 5v i2c sensor

NETMF & Gadgeteer
1

I have to connect 3 i2c pressure sensors to my Cerb40.Two sensors are operating at 3.3v and the third one is operating at 5v.

The 2 two 3.3 sensors are MS5611 barometric pressure sensors and they are already operational:
http://www.meas-spec.com/downloads/MS5611-01BA03.pdf

I have to add this HCLA differential pressure sensor:

The HCLA sensors are also available with 3.3v interface. Unfortunately, I have to experiment now with the 5v sample that I have.

The idea is to power the HCLA sensor at 5v while the others are powered at 3.3v. And then to share the ground and the i2c lines.

My question is:
Is this wise? Is it possible to mix 3.3 and 5v devices through one 12c interface?

Thanks, Sinan

2

The datasheet for the sensor indicates that High Level on I2C lines should be in the range of 90-100% of Vs. For 5V supply it is in the range of 4.5-5V. I am afraid it will not work with additional level shifting components.

3

@ Architect,

Are these requirements coming from the Cerb40 documentation?

And, do you have any references build a simple level shifter. As a software guy, I am completely lost in this.

4

No, as Architect said that’s from the sensor’s datasheet. Page 9 of the PDF you linked to.

Simplest form: https://www.sparkfun.com/products/8745

1 Like
5

@ sinan

I was about to suggest https://www.sparkfun.com/products/8745 , but Brett already did it.

Please check the comments on the sparkfun page as well.

6

I have one of these in house from a previous project. I am wondering if this can be used instead of the Sparcfun component.
http://store.3drobotics.com/products/i2c-smbus-voltage-traslator

This image suggest one way only interface (5v board → 3.3v device)
https://docs.google.com/file/d/0BzPjLNusr5lKOTMxNWUwY2MtNGJlNC00ZDViLWFhNDctYjMyZTU1MWRkN2Jk/edit?hl=en&pli=1

7

No, unfortunately, this one will not work in this case.

8

@ Architect, Bret,

Thanks, I will order the SparcFun converter. Meanwhile, I am going to interface the sensor to a 5v Arduino board to experiment a little bit.

Cheers, Sinan

9

Also check out the ADUM1251ARZ from Analog Devices.

This is a nice little digital isolator and level switcher that works with I2C.

I use this in a design where the ADC is isolated power wise from the processor but you can common the grounds and use it as a simple level shifter.

10

@ Dave,
Thanks, looks good. Its little overkill (= too pricy) for this project but I will keep it in mind for future projects.