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@erjiang erjiang/usbscale.pl

Last active May 23, 2020
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#!/usr/bin/perl
#
# Eric Jiang
# http://notes.ericjiang.com/posts/54
# This software is public domain.
#
# NOTE: This code is not maintained!
# There is a newer version written in C:
# https://github.com/erjiang/usbscale
#
use bytes;
my $data;
#prevents us from repeating messages
my $waitingflag = 0;
while (1) {
$data = `cat /dev/hidraw4 | head -c 7`;
my $report = ord(substr($data, 0, 1));
my $status = ord(substr($data, 1, 1));
my $unit = ord(substr($data, 2, 1));
my $exp = ord(substr($data, 3, 1));
my $lsb = ord(substr($data, 4, 1));
my $msb = ord(substr($data, 5, 1));
my $weight = ($msb * 256 + $lsb) / 10;
if($exp != 255 && $exp != 0) {
$weight ^= $exp;
}
#print "$report $status $unit $exp $weight\n";
if($report != 0x03) {
die "Error reading scale data!\n";
}
if($status == 0x01) {
die "Scale reports FAULT!\n";
} elsif ($status == 0x02 || $weight == 0) {
if($waitingflag != 0x02) {
print "Zero'd...\n";
$waitingflag = 0x02;
}
} elsif ($status == 0x03) {
if($waitingflag != 0x03) {
print "Weighing...\n";
$waitingflag = 0x03;
}
} elsif ($status == 0x04) {
my $unitName = "units";
if($unit == 11) {
$unitName = "ounces";
} elsif ($unit == 12) {
$unitName = "pounds";
}
print "$weight $unitName\n";
last;
} elsif ($status == 0x05) {
if($waitingflag != 0x05) {
print "Scale reports Under Zero...\n";
$waitingflag = 0x05;
}
} elsif ($status == 0x06) {
if($waitingflag != 0x06) {
print "Scale reports Over Weight!\n";
$waitingflag = 0x06;
}
} elsif ($status == 0x07) {
if($waitingflag != 0x07) {
print "Scale reports Calibration Needed!\n";
$waitingflag = 0x07;
}
} elsif ($status == 0x08) {
if($waitingflag != 0x08) {
print "Scale reports Re-zeroing Needed!\n";
$waitingflag = 0x08;
}
} else {
die "Unknown status code: $status\n";
}
}
@mattismyname

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mattismyname commented Oct 12, 2010

FYI, I just upgraded to Ubuntu 10.10 and the script stopped working. A bit of poking and it seems that you can make it work by shifting the variable indices down by 1:

my $report = ord(substr($data, 0, 1));
my $status = ord(substr($data, 1, 1));
my $unit   = ord(substr($data, 2, 1));
my $exp    = ord(substr($data, 3, 1));
my $lsb    = ord(substr($data, 4, 1));
my $msb    = ord(substr($data, 5, 1));
@erjiang

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erjiang commented Oct 12, 2010

@mattismyname My first reaction is that it doesn't make sense for the variable indices to be shifted in 10.10 unless the USB HID protocol changed or Perl suddenly switched to 1-based indices or something weird. I haven't tried 10.10 yet but I will double-check this script when I do.

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mattismyname commented Oct 12, 2010

Yes, it is weird. Maybe the hidraw kernel driver changed...?

@basilgohar

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basilgohar commented Oct 22, 2010

I can confirm the problem + solution for Fedora 13, 64-bit (not sure if that matters). Shifting the indices down by one made it report the weights again.

@erjiang

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erjiang commented Feb 14, 2011

The indices for the scale data have been shifted down, per mattismyname's investigation.

@basilgohar

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basilgohar commented Feb 14, 2011

Thanks! I'll give this a try and get back with you.

@erjiang

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erjiang commented Feb 14, 2011

I have just finished an early version of a C program that reads USB scales. Try it out and let me know how it goes. https://github.com/erjiang/usbscale

@sanmai

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sanmai commented Jun 6, 2014

Consider using unpack() instead of ord(substr()). Example here.

@joshuaer

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joshuaer commented Jun 23, 2016

Hello, I am trying to use this script with a Metler Toledo PS60. I am able to get the script to talk with the scale, but it is reading the weight incorrectly. For example, a 4lb item will read as 255lb, how in the script can I possibly correct this?

thanks

@bhartvigsen

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bhartvigsen commented Nov 20, 2019

Just a note, this can be adapted for Fairbanks scales by removing the line $weight ^= $exp; and changing / 10 to /100

@erjiang

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erjiang commented Nov 20, 2019

@bhartvigsen Interesting find. Can you open an issue on https://github.com/erjiang/usbscale/issues with details about your scale? It'd be nice to add support for it.

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