This library lets you read weight from a standard USB scale using pure PHP.

Could be ported to other languages with ease, should they have unpack()

Tested with:

• Stamps.com Stainless Steel 5 lb. Digital Scale
• DYMO M25 25 lb Digital Postal Scale

See read_stupid.php or usbscale.c if you want to understand how it works at a glance.

composer require sanmai/usb-scale-reader

And then:

$reader = \USBScaleReader\Reader::fromDevice('/dev/scale');
$weightInGrams = $reader->getWeight();
var_dump($reader, $weightInGrams);

Sample output:

class USBScaleReader\Reader#2 (5) {
  public $report =>
  int(3)
  public $status =>
  int(4)
  public $unit =>
  int(2)
  public $exponent =>
  int(0)
  public $weight =>
  int(144)
}
int(144)

Add to /etc/udev/rules.d/80-persistent-scale.rules:

KERNEL=="hidraw*", ATTRS{manufacturer}=="Maker Name", SYMLINK+="scale"
KERNEL=="hidraw*", SUBSYSTEM=="hidraw", MODE="0664", GROUP="plugdev"

Maker name is either Stamps.com or DYMO.

And then reconnect your scale.

For other makers see:

udevadm info -a -p  $(udevadm info -q path -n /dev/hidrawN)

These rules imply that you should be in plugdev for the scripts to work.

There is also a simple reading program written in C.

To build it and run tests against PHP implementation:

cd example
make test

Usage is as simple as it can be:

./usbscale /dev/hidraw3

Outputs something like

70.87 g