DIY Laundry Weight + Detergent Auto-Measure Module (Step-by-Step)

Save detergent, avoid over/under-dosing, and make laundry foolproof with a small module that measures drum/hamper weight and dispenses the correct detergent dose automatically. This DIY guide shows parts, wiring, calibration, enclosure ideas, and safety tips so you can build a reliable auto-measure module for your washer.

🔍 What This Module Does

The module measures the weight of laundry, calculates the detergent required (based on settings you define: load type, fabric, soil level), and then triggers an electronic dispenser to release the correct amount. It can be used as a standalone smart accessory or integrated with a smart home hub.

🌟 Applications & Benefits

Consistent detergent dosing (saves product & money)
Better washing results (avoids over-sudsing)
Useful for laundromats, families, and care homes
Reduces environmental impact
Optional data logging for usage tracking

🧰 Parts & Components

Load cell (5kg–50kg) with HX711 amplifier
Microcontroller: ESP32 (Wi-Fi) or Arduino Nano (no Wi-Fi)
Peristaltic pump or small DC dosing pump (food-safe)
Solenoid valve (for gravity feed systems)
12V DC power supply (or USB power for controller + separate pump supply)
Buttons or rotary switch for mode selection
OLED or LCD display for weight & dose readout
Enclosure (ABS plastic or 3D printed) and mounting hardware
Tubing & connectors (food-safe PVC or silicone)
Optional: RTC module, Wi-Fi/Bluetooth for app integration, flow sensor for verification

⚙️ How It Works — System Overview

Load cell under laundry platform or built into hamper measures weight.
HX711 reads load cell and sends stable weight value to microcontroller.
Microcontroller applies a dosing algorithm (g/weight or ml/kg) based on selected mode.
Controller runs pump or opens valve for an exact time (calibrated) to deliver the required detergent volume.
Optional: send usage data to phone/app or log to SD card for analysis.

🔧 Step-by-Step Build Instructions

1. Mechanical Platform & Load Cell Mounting

Mount the load cell on a rigid base. If measuring hamper weight, place load cell under a small platform sized to hold laundry pile.
Use rubber pads to isolate vibration. Ensure the platform can move slightly so the load cell reads accurately.
Protect the load cell from moisture (use a small plastic cover) and avoid direct detergent spills.

2. Electronics Wiring (Basic)

Connect load cell to HX711 amplifier (E+, E-, A+, A- or B+/B- per module spec).
HX711 -> microcontroller (DT, SCK pins to digital IO).
Pump/solenoid relay -> transistor or MOSFET driver (with flyback diode) if using DC pump.
OLED/LCD -> I2C (SDA/SCL) or parallel connection.
Buttons/switches -> digital inputs with pull-ups.

3. Microcontroller Logic (Pseudo-Flow)

1. Read stable weight (average multiple samples)
2. Subtract tare/empty weight (tare button)
3. Determine load class (small/medium/large) or exact grams
4. Apply dosing formula:
   dose_ml = base_ml + (weight_kg * ml_per_kg) + soil_adjust
5. Convert dose_ml to pump_time (pump_flow_ml_per_sec known):
   pump_time_s = dose_ml / pump_flow_ml_per_sec
6. Activate pump for pump_time_s
7. Display results & log event

4. Calibration

Place known weights and record raw ADC values; build a calibration curve (HX711 -> grams).
Measure pump flow: run pump for 10s into a measuring cup and compute ml/sec.
Set base_ml and ml_per_kg empirically (example: 20 ml base + 30 ml per kg).

5. Enclosure & Mounting

Design an enclosure that keeps electronics away from splashes; place pump near detergent container.
Use quick-connect tubing and secure clamps to avoid leaks.
Consider a snap-in mount or adhesive feet to attach the module to a laundry cabinet or near washer.

🧪 Safety & Best Practices

Use food-safe tubing and pumps if detergent contacts components.
Keep electronics dry and use proper insulation for AC mains or higher voltages.
Install a manual override to dispense or stop the pump anytime.
Prevent overflow: add a float sensor or use a transparent tubing loop to monitor level.
Label detergent container clearly and secure it so it cannot tip over.

📶 Optional Smart Features

Wi-Fi (ESP32): push usage stats to the cloud or a phone app and receive firmware updates.
Bluetooth: local mobile control and manual dispense.
Voice assistants: integrate with Home Assistant, Alexa, or Google Home.
Auto-learning: adjust dosing based on wash outcomes or user feedback.

🔍 Example Code Snippet (Arduino/ESP)

// pseudo-example for reading HX711 and running pump (Arduino-style)
#include "HX711.h"
HX711 scale;
const int PUMP_PIN = 5;
float grams_per_count = 0.002; // set by calibration
float pump_flow_ml_s = 1.2;    // measured value

void setup(){
  pinMode(PUMP_PIN, OUTPUT);
  digitalWrite(PUMP_PIN, LOW);
  scale.begin(DT_PIN, SCK_PIN);
  // tare: set tare offset after powering up
}

void loop(){
  long raw = scale.read_average(10);
  float grams = (raw - offset) * grams_per_count;
  float kg = grams / 1000.0;
  float dose_ml = 20 + (kg * 30); // sample formula
  float pump_time = dose_ml / pump_flow_ml_s;
  digitalWrite(PUMP_PIN, HIGH);
  delay((int)(pump_time * 1000));
  digitalWrite(PUMP_PIN, LOW);
  delay(2000);
}

⚙️ Troubleshooting & Tips

Unstable weight readings: isolate from vibrations, increase averaging, check wiring.
Pump under/over-dispenses: re-calibrate pump_flow_ml_s and check for air in tubing.
Leak: use hose clamps and test for several cycles before regular use.
False dosing: add debounce and confirmation (e.g., only dispense if weight stable for N seconds).

🎯 Final Thoughts

A laundry weight + detergent auto-measure module is a practical, low-cost retrofit that reduces waste and improves wash results. Start with a simple prototype (load cell + pump) and add smart features later. With careful calibration and safety checks, this module becomes a great addition for homes and small laundromats.

DIY Laundry Weight + Detergent Auto-Measure Module