udev_rules_for_linux.md

How to access the Helios DAC without requiring root privileges

Linux systems normally require running with sudo to access USB devices. udev rules can be used to allow access without requiring root privileges.

(This solution has been tested on a Raspberry Pi running Raspbian Stretch 2018-06-27. Other flavors of Linux may work differently.)

1. Create a file heliosdac.rules in /etc/udev with the contents:

    ACTION=="add", SUBSYSTEM=="usb", ATTRS{idVendor}=="1209", ATTRS{idProduct}=="e500", MODE="0660", GROUP="plugdev"
   

2. Create a link in /etc/udev/rules.d to heliosdac.rules:

    cd /etc/udev/rules.d
    sudo ln -s /etc/udev/heliosdac.rules 011_heliosdac.rules
   

3. Make sure the user account communicating with the DAC is in the plugdev group. On a Raspberry Pi, the "pi" user is in the plugdev group by default.

4. Issue the command sudo udevadm control --reload (or restart the computer).

Confirming a device's vendor and product IDs

1. Disconnect the device.
2. In a terminal window, run the command dmesg --follow.
3. Connect the device.

Example output:

[ 8239.754638] usb 1-1.4: new full-speed USB device number 16 using dwc_otg
[ 8244.968718] usb 1-1.4: New USB device found, idVendor=1209, idProduct=e500
[ 8244.968731] usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 8244.968739] usb 1-1.4: Product: Helios Laser DAC
[ 8244.968748] usb 1-1.4: Manufacturer: Gitle Mikkelsen

These are the idVendor and idProduct values used in heliosdac.rules.