Cerb40: Connecting 5v i2c sensor

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

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.

@ 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.

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

@ 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.

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

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

@ 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

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.

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