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2. Hardware Setup
This page covers the full bill of materials, how each component works, and exactly how to wire everything together.
| Component | Quantity | Notes |
|---|---|---|
| ESP32-S3 Development Board | 1 | The firmware is written for the ESP32-S3. Other ESP32 variants are selectable at install time but the S3 is the primary target. |
| NAU7802 24-bit ADC Breakout (Adafruit) | 1 | Used to read the load cell with high precision. Adafruit |
| 5 kg Load Cell | 1 | A standard half-bridge or full-bridge load cell rated for 5 kg. Adafruit |
| AM2320 Temperature and Humidity Sensor | 2 | One goes inside the dry box; one monitors ambient room conditions. Adafruit |
| MFRC522 RFID Reader Module | 1 | Reads 13.56 MHz NFC/RFID tags. US - AMAZON |
| NFC Tags (13.56 MHz, NTAG213 or compatible) | 1 per spool | Attach one to each filament spool you want to track. |
| 10k Ohm Resistor | 4 | Pull-up resistors for the I2C lines of the two AM2320 sensors. |
| Breadboard or custom PCB | 1 | For prototyping the connections. |
| Jumper wires | As needed |
The Adafruit NAU7802 breakout is a high-resolution analog-to-digital converter specifically designed for load cell applications. It communicates over I2C and provides a 24-bit reading of the differential voltage produced by the load cell. The firmware reads this value, subtracts the tare offset (set when the scale is empty), and divides by a calibration multiplier to produce a weight in grams.
The NAU7802 shares the first I2C bus (Wire) with AM2320 sensor #1. Both devices operate correctly on the same bus because they have different I2C addresses.
The AM2320 is a low-cost, accurate combined temperature and humidity sensor. It communicates over I2C at a fixed address of 0x5C. Because both sensors share the same fixed address, they cannot be placed on the same I2C bus. The firmware solves this by using the two independent hardware I2C controllers built into the ESP32-S3:
-
AM2320 #1 (inside the dry box) connects to
Wire(I2C bus 1) on GPIO 4 and GPIO 5. -
AM2320 #2 (outside, measuring ambient) connects to
Wire1(I2C bus 2) on GPIO 8 and GPIO 9.
Each AM2320's SDA and SCL lines require a 10k ohm pull-up resistor connected to the 3.3 V rail. Without these, the I2C bus will not function reliably.
The MFRC522 module reads 13.56 MHz RFID and NFC tags. It communicates via SPI. When a spool is tapped to the reader, the firmware captures the unique tag UID (a hexadecimal string such as A1B2C3D4) and immediately sends a telemetry update to the backend, which uses the UID to look up the matching spool in Spoolman.
Important: The MFRC522 operates at 3.3 V. Do not connect its VCC pin to a 5 V supply, as this will damage the module. Always double-check the voltage label on the pin header before applying power.
All pin numbers refer to the GPIO numbers on the ESP32-S3 development board.
| Module Pin | Connect to |
|---|---|
| VCC | 3.3 V |
| GND | GND |
| RST | GPIO 1 |
| IRQ | Not connected (optional interrupt, not used by the firmware) |
| MISO | GPIO 13 |
| MOSI | GPIO 11 |
| SCK | GPIO 12 |
| SDA (SS) | GPIO 10 |
| Module Pin | Connect to |
|---|---|
| VDD | 3.3 V |
| GND | GND |
| SDA | GPIO 4, with a 10k pull-up to 3.3 V |
| SCL | GPIO 5, with a 10k pull-up to 3.3 V |
| Module Pin | Connect to |
|---|---|
| VDD | 3.3 V |
| GND | GND |
| SDA | GPIO 8, with a 10k pull-up to 3.3 V |
| SCL | GPIO 9, with a 10k pull-up to 3.3 V |
| Module Pin | Connect to |
|---|---|
| VIN | 3.3 V |
| GND | GND |
| SDA | GPIO 4 (shared with AM2320 #1) |
| SCL | GPIO 5 (shared with AM2320 #1) |
| AV | Not connected |
| DRDY | Not connected |
The load cell wires connect directly to the NAU7802 breakout board's differential input terminals according to the Adafruit NAU7802 guide.
| Bus | GPIO Pins | Devices |
|---|---|---|
Wire (I2C bus 1) |
SDA: GPIO 4, SCL: GPIO 5 | NAU7802 ADC, AM2320 #1 (inside) |
Wire1 (I2C bus 2) |
SDA: GPIO 8, SCL: GPIO 9 | AM2320 #2 (ambient) |
| Signal | GPIO Pin |
|---|---|
| SCK | GPIO 12 |
| MISO | GPIO 13 |
| MOSI | GPIO 11 |
| SS (SDA) | GPIO 10 |
| RST | GPIO 1 |
- Use short, neat wiring runs especially for the load cell, as long wires can introduce noise into the ADC reading.
- The pull-up resistors for the AM2320 sensors should be placed as close to the sensor as possible.
- If you notice inconsistent RFID reads, ensure the SPI wires are not running parallel to the I2C or load cell wires, as this can cause interference.
- All logic in the system runs at 3.3 V. Do not use 5 V logic signals on any of the GPIO pins.
Any 13.56 MHz NFC tag (NTAG213, NTAG215, NTAG216, or compatible MIFARE cards) will work. The system only reads the tag's fixed UID - it does not write any data to the tag. You do not need to pre-program the tags in any way. Simply attach one to each filament spool (a small piece of double-sided tape works well) and then scan it in the DryDock dashboard to link it to a Spoolman spool record.