Difference between revisions of "ADC max1027"

Revision as of 10:47, 12 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:

If you don't have one and are a good electronician, you can order a sample at Maxim's website and solder it directly on your board (footprint is available).

Introduction

The Max1027 is an 8 channels 10 bits A/D converter with an integrated temperature sensor.

Hardware

The 8 inputs voltage range is [0 - 3,3V]. Don't try to put higher voltage on ADC inputs !!
By default internal reference voltage is used (2,5V), so if you apply analog values > 2,5V, they will be truncated.
The i.MXL SPI_1 interface is used to communicate with the device.


If you want to use the MAX1027 then you will have to connect #EOC pin (End Of Conversion) to an i.MXL GPIO, configured as Interrupt (see apf9328.c for more details). By default the driver is using CSI_D6 (PortA 10) pin.

Driver

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

"Slow" interface (for temperature or battery level measurements)

Several interfaces in /sys/bus/spi/devices/spi... are created in order to:

• read the 8 analog inputs values: inx_input (in mV)
• read the temperature: temp1_input (in m°C)
• modify the max1027 registers: conversion, setup & averaging

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

These values are only updated each time you launch a conversion and are only dedicated to measure slow evolving greats.

"Fast" interface (frequencies > 10Hz)

In that case you can use /dev interface (using blocking read to wait end of conversion). To create /dev nodes you can use the loadmax.sh script. As driver MAJOR number is dynamically allocated, you may need to update /dev depending on the drivers loaded on you system.

• repeatedly read value of analog input 0 (variable sampling rate = depends on system load):

# cat /dev/max1027/AIN0

• read analog input 0 once:

# time dd if=/dev/max1027/AIN0 bs=2 count=1 > tmp.bin
# hexdump tmp.bin

Chip registers configuration

Independent of the mode, /sys interfaces allow direct access to the corresponding register in the MAX1027:

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

You can also get current (hexadecimal) values of conversion, averaging and setup registers with (for example):

# cat /sys/bus/spi/devices/spi1.0/setup
0x62

For more details on how to use these registers, take a look at the datasheet.

Shell examples

• Get channel 0 and temperature values:

# let conv=0x87; echo $conv > /sys/bus/spi/devices/spi1.0/conversion
# cat /sys/class/hwmon/hwmon0/device/temp1_input
# cat /sys/class/hwmon/hwmon0/device/in0_input

• Get channels [0-7] and temperature values:

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

• Get 4 average values (of 32 conversions) for channel 0:

# let avg=0x3c; echo $avg > /sys/bus/spi/devices/spi1.0/averaging
# let conv=0x84; echo $conv > /sys/bus/spi/devices/spi1.0/conversion

Links

• MAX1027 datasheet on Maxim website
• hwmon documentation