PRESSURE CARRIER - ELECTRICAL AND ASSEMBLY REVIEW

EXTERNAL WIRING (function mapping; confirm cable orientation before assembly)
J1.1 USB_5V       -> sensor brown, supply +
J1.2 GND          -> sensor blue, supply -
J1.3 SENSOR_OUT   -> sensor white, analogue output
J1.4             -> leave unconnected; verify fourth cable conductor first
J2.1 GND          -> OLED GND
J2.2 3V3          -> OLED VCC
J2.3 I2C_SCL      -> OLED SCL; XIAO D5 / GPIO7
J2.4 I2C_SDA      -> OLED SDA; XIAO D4 / GPIO6
XIAO D1 / GPIO3   -> ADC_PRESSURE

The reference identifies an ANAVI 0.96-inch yellow/blue SSD1306 128x64 OLED.
It does not establish a separate display SKU, individual sensor MPN, or
photographed Molex series. The selected Samtec J1 is an adapter header.
Two Samtec SSQ-107-03-G-S-LL sockets support removable XIAO installation.
Check the pin-1 orientation and USB/stack clearance against physical parts.

PULL-UP POPULATION
R3 and R4 default DNP. Verify the OLED module before assembly:
- Existing suitable pull-ups to 3.3V: leave R3/R4 unpopulated.
- No pull-ups: fit both specified 4.7k resistors and verify I2C waveforms.
- Pull-ups to another voltage: resolve the module wiring before connecting.
The correct value also depends on cable capacitance and chosen I2C speed.

CALCULATED CHECKS
R1=R2=10k, 0.1%. Sensor output sees a nominal 20k load, exceeding the
manual's required minimum 10k load; worst resistor tolerance gives 19.98k.
Divider ratio: 0.4995 to 0.5005 from resistor tolerance alone.
Nominal sensor output 0.5-4.5V becomes ADC input 0.25-2.25V.
At 4.5V, the resistor-only worst-case ADC input is 2.25225V.
R1 parallel R2 = 5k; with C1=100nF the nominal filter pole is 318.3Hz.
Firmware must select an ADC range covering that voltage and calibrate it.
Nominal conversion: sensor volts = 2 * measured ADC volts;
pressure_bar = (sensor_volts - 0.5) * 125, subject to sensor calibration.
The sensor's measurement range is distinct from the regulator operating rating.

POWER REVIEW - NOT YET CLOSED
Power through the XIAO USB-C connector. J1.1 is a supply output to the sensor.
Do not use J1 as an additional external supply input in this assembly.
The sensor requires 4.75-5.25V at its terminals. USB cable, module protection,
and sensor cable voltage drops must be included in the loaded measurement.
Sensor maximum supply current and exact OLED maximum current are not stated
in the available reference. A complete power budget cannot yet be signed off.
Measure 5V/3V3 rails with sensor/display connected and Wi-Fi transmitting.

INPUT PROTECTION - NOT YET CLOSED
The existing 10k series divider resistor and 100nF filter are not a qualified
ESD or cable-fault protection network. No additional clamp has been fitted.
A protection design needs the fault voltage/polarity, source impedance,
duration, cable exposure and acceptable leakage/error. A clamp to 3V3 also
needs a power-off/back-power review. Do not treat this draft as fault tolerant.

VALIDATION
Altium Designer 26.10.1: Project > Validate PCB Project completed on
2026-10-15: "Compile successful, no errors found." This uses the current
project reporting settings and does not replace PCB DRC or hardware tests.
Nine No ERC crosses are restricted to the eight unused XIAO GPIO pins and
J1.4. They do not suppress the seven connected circuit nets globally.
Component identifiers and routed copper are preserved. Full PCB DRC,
physical mating and loaded hardware measurements remain outstanding.

SOURCES
https://www.spectronik.com/uploads/topics/17436589569704.pdf (chapter 4)
https://wiki.seeedstudio.com/XIAO_ESP32C3_Getting_Started/
https://files.seeedstudio.com/wiki/XIAO_WiFi/Resources/Seeeduino-XIAO-ESP32C3-SCH.pdf
https://www.crowdsupply.com/anavi-technology/anavi-thermometer/updates/mini-monochrome-oled-displays
https://donation-trainers-kathy-joy.trycloudflare.com/#stripboard-both-mounted