Re: [Paparazzi-devel] HMC5843 magnetometer (Hector Garcia de Marina)

[Prof. Dr.-Ing. Heinrich Warmers]

Hi
we had also same problems  with the HMC5843 on Sparkefun modules.
On one we double the capacitance of  5µF to 10uF.
Then the  module were running.
The new one with the  HMC5883L runs  without problems.
It seems that there is a error on the old chip.
To use the chips with 5V I2c you can use 2 Fets or a level translator ic.
Voltages over 3.3V on the I2c lines can destroy the chip!
On Mikrokopter there use a 200 Ohm series resistors on the i2c line.
We destroy the LPC2148 chip as we use the mikrokontroller motor controllers (5V I2c) and
had situations that the LPC power was down and  the motor controllers not.
Also you will destroy the electronic if the ground wire is broken.

Heinirch

cristina barrado schrieb:

Hi Hector,

Actually there is nothing else connected in the I2C_1 but the HMC board.
Wires are short (2cm) but connector needs to be improved. I may work on this!

Cristina

Hi Cristina,

it seems your problem is in pull-up resistors and/or total bus capacitance.

How many devices are connected to the I2C bus? how length is the bus/wire?

H?ctor

On Mon, Jan 23, 2012 at 1:32 PM, cristina barrado
<address@hidden>wrote:

  

Dear all,

At the ICARUS group (UPC-Barcelona Tech, Spain) we have been trying to set
up a quadrotor for quite a long time. Thanks to Gautier and Michiel we had
it almost set, but we still have some problems with the magnetometer.

We use a Booz2 with LPC21 and BoozIMUv-1.1. Since the magnetometer in the
IMU was not working we tried to connect an HMC4853 (
http://store.diydrones.com/**HMC5843_Triple_Axis_**
Magnetometer_p/br-hmc5843-01.**htm<http://store.diydrones.com/HMC5843_Triple_Axis_Magnetometer_p/br-hmc5843-01.htm>)
board using the I2C_1. The board is set for 5V, thus we connected it to the
UART0+I2C_1 (LTranslated) connector.

Values read from magnetometer are still 0,0,0!! Software seems to be fine
(some debugging using leds tells us that the I2C device is not responding).
Then we looked at the oscilloscope and find out the the SDA lines of the
I2C_1 were only 1.6V (while CLK line was fine!). The most surprising thing
is that voltage levels are OK (close to 3V and 5V on each I2C_1 connector)
when we disconnect the HMC board !!?

Has any of you work with the HMC board at 5V?? Do we need to add new pull
up resistors? The Booz2 board already has them...

Thanks!

Cristina Barrado
Barcelona Tech

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