Level Shift 5 & 3.3

Projects General Guidance
1

Converting system from the Mega down to the Pro Mini 5V. I think I blew the 3.3 Regulator on my Mega by I2C'sing 3.3 and 5V together.

4" x 6" double sided perfboard

Arduino Pro Mini 5V 16Mhz

3.3V 0.8A Voltage Regulator

5.0V 1.0A Voltage Regulator

BMP085 Barometer/Temperature Sensor

HH10D Hygrometer

BlueSmirf RP-SMA

DS1307 RTC

2x I2C Level Shifter

The power source is 9VDC nominal.

The BMP085 is 3.3V I2C.

The HH10D is 3.3V I2C with a frequency output for data processing.

The DS1307 is 5.0 V I2C.

First question: How can I correctly I2C the voltage mixture? Since I'm using a 5V board, do I run the BMP085 and HH10D through the level shifter to bring them up to 5V, or do I run the DS1307 through it and bring it down to 3.3V? i am assuming the former?

Second Question: Can I just connect the +5 of the Mini, VCC of the DS1307, and VCC of the BlueSmirf to the 5 volt regulator, and the BMP085 and HH10D to the 3.3V regulator? That way I don't have to worry about current consumption through the board itself, all it has to do is take in the I2C lines and the frequency output of the HH10D.

2

Seems like you need a bi-directional level shifter for the 2 low-voltage I²C devices.

Google for "AN97055". A very useful document!

Edit: seems like the sparkfun thing will work. The appnote explains how it works in great detail.

3

Do I need one shift board per sensor, or can I combine both 3.3V sensors, and just use one shift board to jump to 5V with the I2C from the clock?

4

magnethead794:
Do I need one shift board per sensor, or can I combine both 3.3V sensors, and just use one shift board to jump to 5V with the I2C from the clock?

I'm assuming I can combine the 3V3 sensors, but would like conformation so I can alot space on the board..

5

The app_note mentioned by madworm shows how to make your own 3V-5V interface, so does the sparkfun board's schematic.

Providing each I2C device has its unique address then they can share SDL and SCK.