mfraser
Posts: 19
Joined: Thu Oct 18, 2012 2:52 pm

Bright Pi I2C 5 volt and 3 volt

Tue Feb 17, 2015 4:56 pm

I currently have a Raspberry Pi B+ with a HTU21D-F Temperature + Humidity Sensor from Adafruit connected to I2C. I would like to add a Bright Pi from www.pi-supply.com also on I2C, but I'm concerned about having the HTU21D-F running off 3.3V and the Bright Pi running off 5V.

Looking at the specification for the HTU21D-F it does seem to be OK with 5 volts, but are there other options in case I have something that won't work from 5 volts?

vthielen
Posts: 35
Joined: Wed Mar 05, 2014 9:32 am

Re: Bright Pi I2C 5 volt and 3 volt

Thu Feb 19, 2015 12:31 pm

You can find some methods on this page:
http://www.savagecircuits.com/content.p ... 3V-Devices

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mikronauts
Posts: 2710
Joined: Sat Jan 05, 2013 7:28 pm
Contact: Website

Re: Bright Pi I2C 5 volt and 3 volt

Thu Feb 19, 2015 2:50 pm

Hi,

Pi Jumper provides both 3v3 and 5V I2C headers:
http://www.mikronauts.com/raspberry-pi/pi-jumper/

Adafruit also has an I2C buffer module.
mfraser wrote:I currently have a Raspberry Pi B+ with a HTU21D-F Temperature + Humidity Sensor from Adafruit connected to I2C. I would like to add a Bright Pi from http://www.pi-supply.com also on I2C, but I'm concerned about having the HTU21D-F running off 3.3V and the Bright Pi running off 5V.

Looking at the specification for the HTU21D-F it does seem to be OK with 5 volts, but are there other options in case I have something that won't work from 5 volts?
http://Mikronauts.com - home of EZasPi, RoboPi, Pi Rtc Dio and Pi Jumper @Mikronauts on Twitter
Advanced Robotics, I/O expansion and prototyping boards for the Raspberry Pi

pjr_pdco
Posts: 17
Joined: Thu Jan 08, 2015 6:08 pm

Re: Bright Pi I2C 5 volt and 3 volt

Fri Feb 20, 2015 2:03 pm

From a review of the datasheet for the Semtech SC620 it looks to me it would be OK to power the BrightPi from 5v and connect the SDA & SCL to the Pi I2C port ( connect the SC620 & Pi GND also ). A device operation from 5v does not also mean/require the I2C bus pins are operating at 5V too. The I2C bus pull up's are provided by the Pi to 3.3v. The datasheet specifies a minimum level of 1.6V on a I2C bus line to be considered HIGH ( spec for VB-IH on page 4 ) . So 3.3V should be OK

Pat

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mikronauts
Posts: 2710
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Re: Bright Pi I2C 5 volt and 3 volt

Fri Feb 20, 2015 2:33 pm

Yes, as long as the I2C module does not pull up SDA & SCL to 5V it should be fine.
http://Mikronauts.com - home of EZasPi, RoboPi, Pi Rtc Dio and Pi Jumper @Mikronauts on Twitter
Advanced Robotics, I/O expansion and prototyping boards for the Raspberry Pi

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