Qualcomm Pressure Sensing System — Yocto BSP Integration

Piezoresistive Pressure Sensor + ADS1115 ADC + Qualcomm SoC + Yocto BSP

This repository provides a complete implementation for integrating a piezoresistive pressure sensor with a Qualcomm-based development board using Yocto Project Build System.

It includes a custom Yocto meta-layer, device-tree overlay, kernel fragment, systemd service, and a Python daemon for real-time pressure monitoring.

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Project Overview

This project reads analog pressure from a piezoresistive pressure sensor (PDF included in docs/) using an ADS1115 ADC and exposes the data via IIO subsystem on Qualcomm hardware.

✔ Works on:

• Qualcomm Snapdragon boards (C8750, APQ8096, APQ8098, RB3/RB5, etc.)
• Any Yocto-based BSP with available I²C interface

✔ Provides:

• Yocto Layer: meta-pressure/
• Kernel Config Fragment
• Device Tree Overlay for ADS1115
• Python Pressure Daemon
• Systemd service
• Wiring instructions
• Original sensor technical PDF

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Repository Structure

pressure-qualcomm-project/
│
├── README.md              → Project overview & instructions
├── LICENSE                → MIT License
│
├── meta-pressure/         → Yocto layer (recipes, DT, daemon)
│   ├── recipes-kernel/
│   ├── recipes-bsp/
│   └── recipes-support/
│
├── dts/
│   └── myboard-ads1115.dts → Device tree overlay for Qualcomm board
│
├── kernel/
│   └── ads1115.cfg        → Kernel fragment enabling IIO + ADS1115
│
├── software/
│   ├── pressure_daemon.py → Python daemon (reads IIO sysfs)
│   └── pressure.service   → systemd unit
│
├── wiring/
│   └── WIRING.md          → ADS1115 + Sensor + Qualcomm wiring
│
└── docs/
    └── Fachbeitrag_Piezo_e.pdf → Technical PDF about the sensor

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Hardware Requirements

✔ Piezoresistive pressure sensor

(Analog bridge output — described in included PDF)

✔ ADC (Recommended)

• Texas Instruments ADS1115 (I2C, 16-bit, differential)

✔ Qualcomm Development Board

Examples:

• TurboX C8750 (Snapdragon)
• RB3 / RB5
• APQ8096 / APQ8098

✔ Power & Wiring

• 3.3V supply for ADS1115
• Common GND
• SDA + SCL connected to Qualcomm board I²C

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Wiring Summary

See full wiring in wiring/WIRING.md

Basic Connection

Sensor	ADS1115	Qualcomm Board
OUT+	AIN0	—
OUT−	AIN1	—
VEX	VCC	3.3V
GND	GND	GND
SDA	SDA	I2C SDA
SCL	SCL	I2C SCL
ADDR	GND	—

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Yocto BSP Integration

1️⃣ Add Layer to Yocto

Edit bblayers.conf:

BBLAYERS += " \
    /path/to/meta-pressure \
"

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2️⃣ Add Kernel Fragment

The file kernel/ads1115.cfg enables:

• IIO subsystem
• I2C
• ADS1015/ADS1115 driver support

Included automatically through: meta-pressure/recipes-kernel/linux/linux-yocto-ads1115.bbappend

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3️⃣ Add Device Tree Overlay

Located at:

dts/myboard-ads1115.dts

Edit the I²C node to match your Qualcomm DTS:

Example:

/soc/i2c@78b6000 {
    status = "okay";

    ads1115@48 {
        compatible = "ti,ads1115";
        reg = <0x48>;
        #io-channel-cells = <1>;
    };
};

The Yocto recipe compiles it into a .dtbo.

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Testing on Board

After flashing the Yocto build:

1. Check ADC on I2C bus:

i2cdetect -y 0

→ Should show 0x48

2. Check IIO device:

ls /sys/bus/iio/devices/

3. View raw reading:

cat /sys/bus/iio/devices/iio:device0/in_voltage0_raw

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Pressure Daemon

Located at:

software/pressure_daemon.py

Features:

• Reads raw ADC data from IIO
• Converts to voltage
• Applies calibration (a, b values via JSON)
• Logs pressure readings
• Triggers warnings when above threshold

Run manually:

python3 /usr/bin/pressure_daemon.py

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Systemd Integration

Enable service:

systemctl enable pressure.service
systemctl start pressure.service

Check status:

systemctl status pressure.service

Logs:

journalctl -u pressure.service -f

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How to Build Full Yocto Image

bitbake core-image-minimal

Or your custom image:

bitbake my-image

Flash to board → daemon starts automatically → pressure logged.

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Documentation

The original technical PDF explaining piezoresistive sensors is included:

docs/Fachbeitrag_Piezo_e.pdf

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License

MIT License — free for commercial and personal use.

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Support & Customization

If you want, I can generate:

✔ A full flowchart ✔ System block diagram ✔ Professional architecture diagrams ✔ Advanced DTS for your exact Qualcomm board ✔ MQTT / Cloud upload support ✔ A GUI for real-time graphing