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Topic: Arduino 5v supply (Read 622 times) previous topic - next topic

sjef

Hello,

I have an Arduino and an Adafruit data logger shield.
I want to log the data from this IMU sensor:

http://viacopter.eu/index.php?page=shop.product_details&flypage=flypage.tpl&product_id=64&category_id=11&option=com_virtuemart&Itemid=53

The sensor has to be connected to the 5v power supply on the Arduino board and the i2c lines are operating at 3.3v.
The i2c lines from the RTC on the data logger shield are operating at 5v because of the pull up resistors R1 and R2 in this schematics:

http://www.ladyada.net/make/logshield/design.html

Because the sensor already has internal pull up resistors, I removed the R1 and R2 pull up resistors of the shield.

When I connect the logger and the sensor to the Arduino, they aren't working correctly.
Both the logger shield and the sensor are working nice when I connect them separately.
Maybe the problem is that the shield also uses the 5v power supply on the Arduino.

I don't fully understand the schematics of the shield, but it seems the shield is using the 5v power supply from the Arduino.

Is this true?
If not, what am I doing wrong?

Thanks in advance!
Sjef

MarkT

mixing 3.3 and 5V on I2C bus isn't really a great idea - you could try pulling up to 3.8V (4.7k pull up to 5V, 15k to gnd) - this should be high enough to work with most 5V inputs yet not take 3.3 inputs too high.
[ I won't respond to messages, use the forum please ]

Docedison

Adafruit sells a really nice little board that is a 4 channel for lack of an immediately better word that will do to translation from to 3V3 -5V for 2 pairs of data. Or you could read the attached App note from NXP (Phillips) get 2 2N7000 Mosfets or their equivalent and build the one described. I did and it was not only easy... It worked and the parts cost me $0.20 US.

Bob
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
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sjef

Thanks for your replies!

I have a logic level converter.
Found some schematics for connecting this board:

http://aeroquad.com/attachment.php?attachmentid=5555&d=1333126134

But, my sensor requires 5v input and outputs 3.3v on the i2c lines.
Could I just power the sensor as a 5v sensor and keep the i2c lines the same as for a 3.3v sensor in the above schematics?

sjef

It didn't work because the RTC and the IMU had the same i2c address, so this topic can be closed.

dhenry

Quote
the RTC and the IMU had the same i2c address


That's really weird.

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