Does anybody know of a USB Postage Scale that's Linux compatible? - linux

Question

I'm looking for a postage scale that already has linux support (drivers, etc) for a shipping system that I'm working on. I'm planning to use Ubuntu 9.04, but I am willing to switch distro's for compatibility.
Does anybody know of any scales that currently work? Is there an open source project that's working on scale drivers or similar?
Thanks!

Answer 1

I use the 5lb stamps.com scale. You can pick it up for $10 if you sign up for an account with them and then cancel it.
To read from it in linux, get this script: http://gist.github.com/503896
Edit the script file to set the proper hidraw device path. You can find the path by running dmesg after you've plugged the scale in. You will see something like "/dev/hidraw2".
After setting the hidraw path in the script, add execute permission and then run it as root:
chmod +x usbscale.pl
sudo ./usbscale.pl
Place an object on the scale and it will print the weight.

Answer 2

Update:
I've created a newer version of my earlier script that mattismyname linked. It's written in C, and you can find it at https://github.com/erjiang/usbscale
To use it, just download the source code and run (inside its directory):
sudo aptitude install libusb-1.0-0-dev
make
./usbscale
You might need to copy the 50-usb-scales.rules to your /etc/udev/rules.d (or run as root, haha) if you run into a permissions error.

Answer 3

Exponent value is passed as signed integer, and weight is passed in little endian byte order. Other answers do not properly account for these factors. See a more comprehensive example here.
<?php
$binary = fread(fopen('/dev/hidraw3', 'r'), 7);
$data = (object) unpack('Creport/Cstatus/Cunit/cexponent/vweight', $binary);
if ($data->report == 0x03 && $data->status == 0x04) {
$data->weight = $data->weight * pow(10, $data->exponent);
if ($data->unit == 0x0B) {
// convert ounces to grams
$data->weight *= 28.349523125;
// and unit to grams
$data->unit = 0x02;
}
if ($data->unit == 0x02) {
echo "{$data->weight} g\n";
} else {
echo "{$data->weight} in other unit\n";
}
}