commit

README.md

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 # scale-code
 
+USB ID: `1446:6a73`
+
+A CLI utility in Go to read weight data from a Stamps.com USB postal scale via HID.
+
+Originally developed to revive old electronics gifted by a family member. This project documents the quirks, bias, and calibration of the device for others interested in low-cost hardware reuse.
+
+---
+
+## Usage
+
+```sh
+go build -o scale-code
+sudo ./scale-code
+```
+
+The program continuously polls the scale and displays the weight in ounces, rounded to the nearest 0.1 oz.
+
+You must run it as root (`sudo`) or use a proper udev rule to grant access to `/dev/hidraw` devices.
+
+---
+
+## Calibration
+
+### Observed Bias:
+
+```
+W  = Stamps.com scale
+WT = Taylor digital scale (Walmart, new)
+
+Test object: consistent, arbitrary small item
+
+W1: 1.9
+W2: 1.9
+W3: 2.0
+
+WT1: 2.0
+WT2: 2.0
+WT3: 2.0
+```
+
+### Adjustment:
+
+A linear correction factor of `0.952` is applied to compensate for the 0.1 oz low bias, yielding more accurate readings.
+
+---
+
+## License
+
+MIT License © firebadnofire 2025
+
+FOSS, for the preservation of still-functional hardware and the freedom to study it.

go.mod

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+module archuser.org/scale-code
+
+go 1.24.4
+
+require github.com/karalabe/hid v1.0.0

go.sum

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+github.com/karalabe/hid v1.0.0 h1:+/CIMNXhSU/zIJgnIvBD2nKHxS/bnRHhhs9xBryLpPo=
+github.com/karalabe/hid v1.0.0/go.mod h1:Vr51f8rUOLYrfrWDFlV12GGQgM5AT8sVh+2fY4MPeu8=

main.go

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+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"math"
+	"os"
+	"os/signal"
+	"time"
+
+	"github.com/karalabe/hid"
+)
+
+const (
+	vendorID     = 0x1446
+	productID    = 0x6A73
+	refreshRate  = 500 * time.Millisecond
+	calibration  = 0.952 // scale correction factor: 2.1 reported = 2.0 actual
+)
+
+func main() {
+	devices := hid.Enumerate(vendorID, productID)
+	if len(devices) == 0 {
+		fmt.Println("❌ Scale not found.")
+		os.Exit(1)
+	}
+
+	device, err := devices[0].Open()
+	if err != nil {
+		fmt.Println("❌ Failed to open scale:", err)
+		os.Exit(1)
+	}
+	defer device.Close()
+	fmt.Println("✅ Scale connected. Reading... (Ctrl+C to quit)")
+
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, os.Interrupt)
+	go func() {
+		<-c
+		fmt.Print("\n👋 Exiting.\n")
+		device.Close()
+		os.Exit(0)
+	}()
+
+	for {
+		buf := make([]byte, 8)
+		n, err := device.Read(buf)
+		if err != nil || n < 6 {
+			fmt.Print("\r⚠️  No data              ")
+			time.Sleep(refreshRate)
+			continue
+		}
+
+		raw := binary.LittleEndian.Uint16(buf[4:6])
+		oz := float64(raw) / 10.0 * calibration
+		rounded := math.Round(oz*10) / 10
+
+		fmt.Printf("\r📦 Weight: %.1f oz       ", rounded)
+		time.Sleep(refreshRate)
+	}
+}