ADC max1027
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 !!
The i.MXL SPI_1 interface is used to communicate with the device.
If you want to use MAX1027 in "fast" mode (ie measure signals with frequencies > 10 Hz) 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).
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
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
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