Troubleshooting I2C module

teganburns · 2013-07-26 02:22

Hey all I'm having a lot of problems interfacing my MPU-9150 module links for PDF's here -->>(http://www.invensense.com/mems/gyro/mpu9150.html)

This is my first time writing a program that communicates using I2C bus. I tried using a few different I2C drivers from obex but with no prevail. Power should be fine(3.3v from the Quickstart board), Checked my wiring (only 2 wires so that shouldn't be an issue).
And i understand I2C communication protocol. (@DavidJames posted this a while back, thank you) http://www.nxp.com/documents/user_manual/UM10204.pdf

My code is a edited version of Jason Dorie's "ITG-3200" (Gyro Module). My guess is that the problem is in the timing...

If anyone wants to try and troubleshoot the code or give suggestions that would appreciated. :thumb:

My edited code-->> https://raw.github.com/teganburns/Mpu-9150.spin/master/README.md

average joe · 2013-07-26 02:48

Are you using pull-ups on both i2c lines? (sda & scl) I've made this mistake before. What is the problem exactly?

Clive Wakeham · 2013-07-26 03:05

So basically you should have 4 wires running from the Quickstart board to the MPU-9150. Power, Gnd, SDA and SCL.

Double check the model number of the "MPU-9150". I once spent two days trying to get a "Real Time Clock" I2C chip to communicate with a Prop to no avail. I nearly gave up then I pulled out a magnifying glass and realised that I had the wrong chip and its commands were completely different. Then it took me half an hour to put together an object for it.

teganburns · 2013-07-26 03:56

@average joe The chip is on a board from sparkfun.com so it has resistors included.

My problem is in the code... i have spent weeks trying to figure out what's wrong.

@Clive Wakeham i can't make out what it says on the chip but i don't think sparkfun would make the mistake of using the wrong chip (I should have mentioned that its on a board) https://www.sparkfun.com/products/11486

Clive Wakeham · 2013-07-26 05:19

Have you downloaded the Basic I2C Driver?

One of the James Extra bits is a method of calling a I2C address and getting a response from it.

Check it out to confirm that the module you got is on the I2C bus and responding to its 7 bit address.

This the first thing I do now (after the issue with the RTC chip) to ensure the I2C device is connected correctly to the Prop.

All you need to do is write a simple program that queries the address of the module and prints OK on the screen using Parallax Serial Terminal etc.

TrapperBob · 2013-07-26 05:53

Please check the 7-bit address is correct

ChrisGadd · 2013-07-26 08:24

I think Clive and TrapperBob have it. The device ID is indeed %0110_1000, but it needs to be shifted left one bit and a write(0) or read(1) bit shifted in. Your WriteByte methods should use %1101_0000, and your reads should use %1101_0001.
The datasheet also describes clock-stretching by slave devices, though it's not clear if the MPU-9150 makes use of it.

teganburns · 2013-07-26 09:36

Yepp It was the Device Address Thanks!!

Funny how how i wrote the internal register preliminary configuration correctly but got the device address wrong.. :P

Clive Wakeham · 2013-07-26 18:26

If that is the problem then its an easy fix.

In my last post I forgot to mention that I quickly wrote a short spin program that used the Basic I2C driver "extra bits" to cycle through all the 7 bit addresses to find where the I2C device is at.

There is an assembly language version of the I2C driver on OBEX which runs at a faster speed to the spin version.

Troubleshooting I2C module

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