node-red-contrib-usbhid

A node-hid (USB HID device access library) wrapper for nodered

Credit goes to node-hid.

You can look up either git to find information on setup, Prerequisites and Platforms to get the node working: https://github.com/node-hid/node-hid

Prerequisites:

• Node.js v0.8 - v4.x+
• Mac OS X 10.8, Linux (kernel 2.6+), and Windows XP+
• libudev-dev, libusb-1.0-0-dev (if Linux, see Compile below)
• git

node-hid uses node-pre-gyp to store pre-built binary bundles, so usually no compiler is needed to install.

Platforms we pre-build binaries for:

• Mac OS X x64: v0.10, v0.12, v4.2.x
• Windows x64 & x86: v0.10, v0.12, v4.2.x
• Linux Debian/Ubuntu x64: v4.2.x
• Raspberry Pi arm: v4.2.x

How to Use

HID ( USB ) read/write access for non root users ( in my case for user pi on an raspberry pi 4 running nodered )

The Pd-extended [hid] object allows you to access Human Interface Devices such as mice, keyboards, and joysticks. However, in most Linux distributions, these devices are setup to where they cannot be read/written directly by Pd unless you run it as root.

Running a non-system process as root is considered a security risk, so an alternative is to change the permissions of the input devices so that pd can read/write them.

sudo mkdir -p /etc/udev/rules.d
sudo nano /etc/udev/rules.d/51-blink1.rules

Now add the following rules to /etc/udev/rules.d/51-blink1.rules:

SUBSYSTEM=="input", GROUP="input", MODE="0666"
SUBSYSTEM=="usb", ATTRS{idVendor}=="27b8", ATTRS{idProduct}=="01ed", MODE:="666", GROUP="plugdev"
KERNEL=="hidraw*", ATTRS{idVendor}=="27b8", ATTRS{idProduct}=="01ed", MODE="0666", GROUP="plugdev"

And replace 27b8 and 01ed with your device idVendor/idProduct or add this generic rules for ALL devices:

SUBSYSTEM=="input", GROUP="input", MODE="0777"
SUBSYSTEM=="usb", MODE:="777", GROUP="plugdev"
KERNEL=="hidraw*", MODE="0777", GROUP="plugdev"

Reload udev rules

sudo udevadm control --reload-rules

Unplug and plug back your HID device

Then create an "input" group and add yourself to it:

sudo groupadd -f input
sudo gpasswd -a $USER input

Reboot your machine for the rules to take effect. Your nodejs / nodered has now FULL ACCESS !! to you usb devides. Feel free to adjust the permissions to fit your needs.

Parse keys

The buffer that is sent to the output needs to be parsed in order to detect the key pressed. To detect the key you can use a function node with this code:

var keymap = {'04':'A','05':'B','06':'C','07':'D','08':'E','09':'F','0a':'G','0b':'H','0c':'I','0d':'J','0e':'K','0f':'L','10':'M','11':'N','12':'O','13':'P','14':'Q','15':'R','16':'S','17':'T','18':'U','19':'V','1a':'W','1b':'X','1c':'Y','1d':'Z','1e':'1','1f':'2','20':'3','21':'4','22':'5','23':'6','24':'7','25':'8','26':'9','27':'0','00':''}
var hex = Buffer.from([msg.payload[3]]).toString('hex');

var key = keymap[hex]

For more info check:

• https://github.com/node-hid/node-hid/issues/228#issuecomment-408710289
• https://github.com/imyelo/hid-scanner
• https://github.com/imyelo/hid-scanner/blob/master/lib/keymap.raw.json