Difference between revisions of "ADC max1027"

Revision as of 09:40, 7 September 2008

Instructions to install and use the MAX1027 ADC. This device is an option of the APF9328 boards. To know if you have one on your board, take a look at the connectors side:

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/devices/ 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:

# let conv=0xb9; echo $conv > /sys/bus/spi/devices/spi1.0/conversion

For more details, take a look at the datasheet.

Links

• MAX1027 datasheet on Maxim website