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[on:]

Hello everyone,

I am relatively new to developing with Arduino and the field of electrical engineering in general so I am looking for a more experienced eye to look over my work to prevent any costly mistakes before they occur (and clear up any confusion I have.)

I have purchased an ATAVRSBIN2 (Datasheet) and would like it to cooperate with the Arduino (Uno).

I have managed to find one other topic regarding both the ATAVRSBIN2 and Arduino (link)but I am a bit confused and before I hastily attempt to do something (and ruin something), I want to make sure my setup looks good.

My current strategy (unimplemented) is to use the GND, PWR, SDA and SCL to use I2C with the Arduino.

Question 1: Can I safely use the 3.3V from my Arduino to power the device?

Question 2: Do I need a 4K7 pull-up resistor for the SDA/SCL connections (as specified here) or am I correct when I read "The I2C pull-up resistors are included on the Inertial Two Sensors Xplained board. " (Top of page 4 in the datasheet).

Question 3: In the article/blog I referenced, the two of them used a "logic level converter" (link), do I need this and what purpose is it serving? (From my understanding, it's just regulating 5V to 3.3V; which I believe my Arduino board already does for me.)

Thanks in advance, sorry if this board is not intended for this. I tried to be detailed in my questions but if I missed anything, just let me know.

[Reply #1 on:]

1 : Yes, you should use the 3.3V for the 9DOF board.
2 : No, the 9DOF board already contains pull-up resistors of 2k2. Also that level shifter contains pull-up resistors.
3 : Yes, the sensor chips use 2.5V. You should use a level shifter for the signals. Since the low side is 2.5V, the level shifter low voltage should be connected to the 2.5V of the 9DOF board. I think that 2.5V is not on a pin on the header, so you have to solder a wire to the 2.5V on the board.

I'm not sure how many level shifters you need. Is it only for the I2C-bus (SDA and SCL) ?
This page is about the I2C levels : http://playground.arduino.cc/Main/I2CBi-directionalLevelShifter

Other 9DOF sensor boards would be more suitable for the 5V Arduino Uno.

[Reply #2 on:]

The Arduino internal pull up resistors are 20k http://www.arduino.cc/en/Tutorial/DigitalPins

[Reply #3 on:]

The Arduino internal pull up resistors are 20k

sp. "The Arduino internal pull up resistors are a minimum 20k, with a maximum of 50kohms" (ref. ATmega datasheet)

[Reply #4 on:]

Thanks for the great information.

Question three really was the one that stumped me Because it stated "The Inertial Two Sensors Xplained development board has an onboard 2.5V regulator to supply power to all three sensors." I'm glad to have that cleared up and it looks like I'll need to find either a level converter or another sensor board.

EDIT: I think I understand now. The A4/A5 pins used for SDA and SCL are 5V and we need to protect the sensor from that 5V source. Thus the level converter shifts those signals to/from 5V to 3.3V, correct? The power isn't so much the issue because that is regulated to 3.3V from the Arduino Uno.

The reason I got this sensor board is because it was affordable and available at Digi-Key. I get same day delivery on my Digi-Key orders and it was really the only one I could find on their website.

Are there any sensor board you would recommend that are in the same price range (preferably available from Digi-Key)?

Thanks again

[Reply #5 on:]

The sensors use 2.5V, so also the I2C signals of the sensors are 2.5V.

The level shifter protects the sensors from the 5V signals from the Arduino, but also raises the 2.5V signal from the sensors to the 5V signal of the Arduino. It's in both directions.
To be able to do that, the level shifter needs the high voltage (5V) and the low voltage (2.5V). That's why I wrote that the low voltage must be connected to the 2.5V on the sensor board somewhere.

If you take a look at the websites of Sparkfun and Adafruit, you will find more suitable sensors for the Arduino.

[Reply #6 on:]

Alright, I'll look online. Looks like there is no escaping an online order.

I'll likely just buy a new sensor and I'll just be out $20 on this one (all part of the learning process). Maybe in the future I will have more experience and will find a use for it.

Thanks again for all the help.