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Topic: Level Shift 5 & 3.3 (Read 1 time) previous topic - next topic

magnethead794

Nov 17, 2011, 07:57 am Last Edit: Nov 17, 2011, 05:28 pm by magnethead794 Reason: 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.
KF5RVR

madworm

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.
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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?
KF5RVR

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..
KF5RVR

Runaway Pancake

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.
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