The parts in detail¶

What each module does and the numbers you need when something misbehaves.

┌───────────────────────────────────────────┐
│           WT32-SC01 Plus                  │
│                                           │
│  ESP32-S3 ───── 480x320 Touchscreen       │
│      │                                    │
│      │ I2C  (SDA GPIO10, SCL GPIO11)      │
│      ├─────────────── PN532 NFC Reader    │
│      │                                    │
│      └─────────────── NAU7802 ADC         │
│                            │              │
│                        Load Cell          │
└───────────────────────────────────────────┘

WT32-SC01 Plus¶

The brain and the display in one board.

Property	Value
MCU	ESP32-S3
Display	3.5" IPS, 480x320, ST7796
Touch	FT6336U, capacitive
PSRAM	Quad (QSPI)
External I2C	SDA `GPIO10`, SCL `GPIO11`

Both external modules hang off the I/O connector, an 8 pin socket into which the supplied 7 pin cable goes flush to the left. Getting that one pin wrong leaves both modules unpowered, which the scale reports as Nothing on the I2C bus.

PN532 NFC reader¶

Reads and, since v0.7.0, writes NFC tags.

Property	Value
Interface	I2C
I2C address	`0x24`
Frequency	13.56 MHz
Protocol	ISO 14443A
Pins	SDA `GPIO10`, SCL `GPIO11`, RST `GPIO14` (pin 7, brown) - see Wiring

Set the DIP switches before you solder

The PN532 has to be in I2C mode: SW1 = ON, SW2 = OFF. In HSU or SPI mode it does not answer on the I2C bus at all. Changing the switches after the module is mounted is awkward, so do it first.

5V, and not through the NAU7802

The PN532 needs 5V from pin 1 of the I/O cable. The NAU7802's STEMMA QT passthrough only carries 3.3V - do not daisy-chain through it.

What it can and cannot read is on the NFC tags page.

NAU7802 load cell ADC¶

A 24 bit ADC built for bridge sensors, which is what a load cell is.

Property	Value
Interface	I2C
I2C address	`0x2A`
Resolution	24 bit
Pins	SDA `GPIO10`, SCL `GPIO11`

The load cell's four wires go to the screw terminals:

Load cell wire	Terminal	Function
Red	`E+`	Excitation +
Black	`E-`	Excitation -
White	`A+`	Signal +
Green	`A-`	Signal -

Numbers going down when you add weight

A+ and A- are swapped. See Load cell reversed.

Third party STEMMA QT cables

On ready-made cables from third parties the pin order often does not match the WT32 cable. Check wire by wire rather than trusting colours.

Load cell¶

A 2 kg YZC-133 beam cell is recommended; 5 kg works but is slightly less precise at low weights. Most spools sit well inside 2 kg.

Checking the bus¶

If something is not answering, the scale tells you which chip and why - see What the scale is telling you. On the serial monitor at 115200 baud, the boot line I2C_EXT scan: lists every address that answers. Expect 0x24 and 0x2A.