Controlling the Analog Devices AD7746 Evaluation Board under Linux

The Analog Devices EVAL_AD7746EB is a low cost evaluation board for the AD7746 capacitance to digital converter. This board uses a Cypress FX2 as a USB-I2C bridge. The kit ships with a Windows GUI that provides basic control of the device. The GUI is written in LabView and Analog has provided this code as a demo. They do not provide support for communicating with this board using other means.

This code provides a simple example of how to communicate with the board using fxload and libusb in C under Linux, using the Analog-provided FX2 firmware.

Install

1. Install prerequisites:

    sudo apt-get install libusb-dev
    sudo apt-get install fxload
   

2. Optional: You can skip this step and just use the firmware file in this repo. Download and install the Analog Devices EVAL-AD7746 software for Windows. Grab this firmware file and copy it to ./firmware/Icv_usb.hex:

    C:\Program Files (x86)\Analog Devices\AD7745-46EB\data\Icv_usb.hex
   

3. Build and install.

    make
    sudo make install
   

Usage

Plug the board into USB and run the example program:

$ ./eval_ad7746eb
time: 1593624499.785889  capacitance_raw: 80f720  capacitance_pF: 0.061781  temp_raw: 8434629  temp_C: 22.471
time: 1593624499.956193  capacitance_raw: 80f697  capacitance_pF: 0.061647  temp_raw: 8434684  temp_C: 22.498
time: 1593624500.181381  capacitance_raw: 80f6b2  capacitance_pF: 0.061674  temp_raw: 8434666  temp_C: 22.489
time: 1593624500.417508  capacitance_raw: 80f6f0  capacitance_pF: 0.061734  temp_raw: 8434689  temp_C: 22.500
time: 1593624500.643616  capacitance_raw: 80f693  capacitance_pF: 0.061644  temp_raw: 8434671  temp_C: 22.492

or log data to a file:

./eval_ad7746eb > data.log 2>/dev/null

You can modify the config_ad7746() and config_board() functions as needed for your application.

Troubleshooting

When the eval board is plugged in, the udev rule will invoke fxload to load the firmware. You can check that the device was detected:

$ lsusb -d 0456:b481
Bus 001 Device 003: ID 0456:b481 Analog Devices, Inc.

You should see something like this in syslog indicating firmware was loaded:

$ tail /var/log/syslog
Jul  1 16:19:59 hostname kernel: [74691.005245] usb 1-1: new high-speed USB device number 16 using musb-hdrc
Jul  1 16:19:59 hostname kernel: [74691.153842] usb 1-1: New USB device found, idVendor=0456, idProduct=b481, bcdDevice= 0.00
Jul  1 16:19:59 hostname kernel: [74691.153890] usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
Jul  1 16:20:00 hostname root: AD7746EB firmware loaded.

There was a note in the Analog docs that the USB microcontroller would lock up if the I2C communication fails. I did not see any failures, but beware.

If the device is unplugged or a communication failure occurs the program will exit.

The settings in config_ad7746() are specific to my application. You will need to change them for your hardware.