Difference between revisions of "ADC max1027"

Revision as of 22:57, 10 December 2007

Instructions to install and use the onboard ADC (MAX1027)

Introduction

The Max1027 is a 8 channels 10 bits A/D converter with an integrated temperature sensor.
The 8 inputs voltage range is 0 - 3,3V. Don't try to put higher voltage on ADC inputs !!
The i.MXL SPI_1 interface is used to communicate with the device.
For the Linux kernel, the Max1027 is considered as a Hardware Monitoring device. For the moment only a low speed interface (/sys) is available: the eight channels and the temperature are updated every 10ms.

Installation

From the top directory:

# make linux-menuconfig

Then select in Device Drivers->SPI support->Freescale iMX SPI controler driver (builtin not module !!)

Then select in Device Drivers->Hardware Monitoring Support->MAX1027 sensor chip (Module)

Once the new config saved, rebuild your image

# make

and copy hwmon.ko and max1027.ko driver to your target or reflash your rootfs.

On the target, the driver can be started like this:

# insmod /lib/modules/drivers/hwmon/hwmon.ko
# insmod /lib/modules/drivers/hwmon/max1027.ko

or like this if you reflashed your rootfs:

# modprobe max1027

Usage

Several interfaces in /sys/bus/spi/are created in order to

• read the 8 inputs (inx_input). Result in mV
• read the temperature (temp_input). Result in deg celsius
• modify the default configuration (config and conv)

An input can be read like that

# cat /sys/bus/spi/devices/spi1.0/in0_input

The temperature can be read like that

# cat /sys/bus/spi/devices/spi1.0/temp1_input

The two configurations files allow direct access to the corresponding register in the MAX1027. For more details, take a look at the datasheet

• http://datasheets.maxim-ic.com/en/ds/MAX1027-MAX1031.pdf

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