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185 changes: 185 additions & 0 deletions docs/tutorials/class-d-audio-amplifier-hat.mdx
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---
title: Class D Audio Amplifier HAT
description: Learn how to build a 3W stereo Class D audio amplifier HAT using the PAM8403 amplifier chip, speaker terminals, and volume control with tscircuit.
---

## Overview

In this tutorial, we will build a **Class D Audio Amplifier HAT**. This board takes stereo line-level audio input and amplifies it to drive two 3W speakers (Left and Right channels) with excellent efficiency and minimal heat output.

Unlike traditional analog amplifiers (such as Class A or AB) which dissipate excess power as heat, **Class D amplifiers** work by converting the analog input into a high-frequency PWM (Pulse Width Modulation) signal. The output MOSFETs switch fully ON or fully OFF rapidly, leading to efficiencies up to 90%, making them perfect for battery-powered or compact projects like Raspberry Pi audio HATs.

We will use the **PAM8403** Class D amplifier chip, which is a filterless 3W stereo amplifier requiring minimal external components.

---

## 📋 Components Checklist

Our amplifier HAT will consist of:
1. **PAM8403 Class D Amplifier (U1)** — 3W stereo audio amplifier in an SOP-16 package.
2. **Dual-Gang 10kΩ Potentiometer (RV1)** — Standard stereo volume control dial.
3. **2x 2-pin Screw Terminals (J1, J2)** — Speaker output blocks for Left and Right speakers.
4. **40-pin Raspberry Pi Header (J3)** — Pi HAT connector for power (5V) and audio line signals.
5. **Bulk Decoupling Capacitor (C1)** — 470µF electrolytic capacitor to buffer high-current speaker transients.
6. **Filtering Capacitors (C2, C3, C4, C5)** — Small ceramic capacitors (0.1µF to 1µF) to filter power supply noise and input signals.

---

## 🛠️ Step-by-Step Implementation

Create a new file in your project or editor and paste the following tscircuit design code.

### Complete Circuit Code

import TscircuitIframe from "@site/src/components/TscircuitIframe"

<TscircuitIframe defaultView="schematic" code={`
export default () => {
return (
<board width="65mm" height="56mm">
{/* 40-pin Raspberry Pi Hat Header */}
<chip
name="J3"
manufacturerPartNumber="RPI-HAT-HEADER-40P"
schX={-20}
schY={0}
pinLabels={{
pin2: "5V",
pin6: "GND",
pin12: "AUDIO_L",
pin35: "AUDIO_R",
}}
/>

{/* PAM8403 Class D Amplifier */}
<chip
name="U1"
manufacturerPartNumber="PAM8403"
schX={10}
schY={0}
pinLabels={{
pin1: "+OUT_L",
pin2: "PGND_L",
pin3: "-OUT_L",
pin4: "PVDD_L",
pin5: "MUTE",
pin6: "VDD",
pin7: "IN_L",
pin8: "SNS",
pin9: "BYP",
pin10: "IN_R",
pin11: "SHDN",
pin12: "PVDD_R",
pin13: "-OUT_R",
pin14: "PGND_R",
pin15: "+OUT_R",
pin16: "VREF",
}}
/>

{/* 10k Dual-Gang Potentiometer for volume control */}
<chip
name="RV1"
manufacturerPartNumber="POT-STEREO-10K"
schX={-5}
schY={-12}
pinLabels={{
pin1: "L_IN",
pin2: "L_WIPER",
pin3: "L_GND",
pin4: "R_IN",
pin5: "R_WIPER",
pin6: "R_GND",
}}
/>

{/* Speaker Output Screw Terminals */}
<chip
name="J1"
manufacturerPartNumber="SCREW-TERMINAL-2PIN"
schX={25}
schY={10}
pinLabels={{
pin1: "SPK_L+",
pin2: "SPK_L-",
}}
/>
<chip
name="J2"
manufacturerPartNumber="SCREW-TERMINAL-2PIN"
schX={25}
schY={-10}
pinLabels={{
pin1: "SPK_R+",
pin2: "SPK_R-",
}}
/>

{/* Input Coupling Capacitors */}
<capacitor name="C4" capacitance="1uF" schX={0} schY={0} />
<capacitor name="C5" capacitance="1uF" schX={0} schY={-5} />

{/* Decoupling & Bypass Capacitors */}
<capacitor name="C1" capacitance="470uF" schX={5} schY={12} />
<capacitor name="C2" capacitance="0.1uF" schX={10} schY={12} />
<capacitor name="C3" capacitance="1uF" schX={15} schY={12} />

{/* Connections */}
{/* Power Rails (5V & GND) */}
<trace from=".J3 .pin2" to="net.5V" />
<trace from=".J3 .pin6" to="net.GND" />

{/* PAM8403 Power Pin connections */}
<trace from="net.5V" to=".U1 .pin4" /> {/* PVDD_L */}
<trace from="net.5V" to=".U1 .pin12" /> {/* PVDD_R */}
<trace from="net.5V" to=".U1 .pin6" /> {/* VDD */}
<trace from="net.5V" to=".U1 .pin5" /> {/* MUTE disabled (pulled high) */}
<trace from="net.5V" to=".U1 .pin11" /> {/* SHDN disabled (pulled high) */}

<trace from="net.GND" to=".U1 .pin2" /> {/* PGND_L */}
<trace from="net.GND" to=".U1 .pin14" /> {/* PGND_R */}

{/* Power Filtering Caps */}
<trace from="net.5V" to=".C1 .pin1" />
<trace from=".C1 .pin2" to="net.GND" />
<trace from="net.5V" to=".C2 .pin1" />
<trace from=".C2 .pin2" to="net.GND" />

{/* Bypass Reference Capacitor */}
<trace from=".U1 .pin9" to=".C3 .pin1" />
<trace from=".C3 .pin2" to="net.GND" />

{/* Audio Input Left Connection */}
<trace from=".J3 .pin12" to=".RV1 .pin1" />
<trace from=".RV1 .pin3" to="net.GND" />
<trace from=".RV1 .pin2" to=".C4 .pin1" />
<trace from=".C4 .pin2" to=".U1 .pin7" /> {/* IN_L */}

{/* Audio Input Right Connection */}
<trace from=".J3 .pin35" to=".RV1 .pin4" />
<trace from=".RV1 .pin6" to="net.GND" />
<trace from=".RV1 .pin5" to=".C5 .pin1" />
<trace from=".C5 .pin2" to=".U1 .pin10" /> {/* IN_R */}

{/* Left Speaker Output */}
<trace from=".U1 .pin1" to=".J1 .pin1" />
<trace from=".U1 .pin3" to=".J1 .pin2" />

{/* Right Speaker Output */}
<trace from=".U1 .pin15" to=".J2 .pin1" />
<trace from=".U1 .pin13" to=".J2 .pin2" />
</board>
)
}
`} />

---

## 🔊 Important Audio Circuit Design Notes

1. **Input Coupling Capacitors (C4, C5)**:
- These DC-blocking input capacitors are absolutely critical. They block any DC bias voltage from the host audio source while allowing the AC audio waveform to pass into the PAM8403 input pins.
2. **Bulk Capacitance (C1)**:
- Class D amplifiers switch high currents to drive speakers. A large bulk decoupling capacitor (like the 470µF **C1**) must be placed as close to the power pins as possible to handle sudden current draws and prevent power sag.
3. **Filterless Design**:
- The PAM8403 uses a filterless modulation architecture. The inductance of the speaker coils acts as a low-pass filter to recover the audio signal from the PWM carrier, meaning you do not need bulky LC filters at the speaker outputs for short wire lengths.
146 changes: 146 additions & 0 deletions docs/tutorials/i2c-environmental-sensor.mdx
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---
title: I2C Environmental Sensor Module
description: Learn how to design a compact environmental monitoring module with a BME280 sensor, SSD1306 OLED display, and I2C bus pull-ups using tscircuit.
---

## Overview

In this tutorial, we will build a compact **I2C Environmental Sensor Module**. This board is designed to measure ambient temperature, relative humidity, and barometric pressure, and display the live readings on a local OLED screen.

We will use **I2C (Inter-Integrated Circuit)**, which is a popular serial communication protocol that allows multiple slave devices (the BME280 sensor and SSD1306 OLED) to communicate with a single master host using only two signal wires:
- **SDA** (Serial Data)
- **SCL** (Serial Clock)

---

## 📋 Components Checklist

Our module will consist of:
1. **BME280 Environmental Sensor (U1)** — Digital sensor for temperature, humidity, and pressure in an LGA-8 package.
2. **SSD1306 OLED Display (U2)** — Standard 0.96-inch 128x64 I2C display panel.
3. **I2C Pull-Up Resistors (R1, R2)** — 4.7kΩ resistors to pull the SDA and SCL signal lines high.
4. **Decoupling Capacitors (C1, C2)** — 0.1µF capacitors to stabilize power supply inputs.
5. **4-pin Male Header (J1)** — Connecting interface for power (VCC/GND) and communication (SDA/SCL) to a host microcontroller.

---

## 🛠️ Step-by-Step Implementation

Create a new file in your project or editor and paste the following tscircuit design code.

### Complete Circuit Code

import TscircuitIframe from "@site/src/components/TscircuitIframe"

<TscircuitIframe defaultView="schematic" code={`
export default () => {
return (
<board width="40mm" height="30mm">
{/* 4-pin Host Connection Header */}
<chip
name="J1"
manufacturerPartNumber="HDR-1X4"
schX={-15}
schY={0}
pinLabels={{
pin1: "VCC",
pin2: "GND",
pin3: "SCL",
pin4: "SDA",
}}
/>

{/* BME280 Sensor */}
<chip
name="U1"
manufacturerPartNumber="BME280"
schX={0}
schY={-8}
pinLabels={{
pin1: "VDD",
pin2: "GND",
pin3: "VDDIO",
pin4: "SDO",
pin5: "SDA",
pin6: "SCL",
pin7: "CSB",
pin8: "GND_IO",
}}
/>

{/* SSD1306 128x64 OLED Display (I2C interface) */}
<chip
name="U2"
manufacturerPartNumber="SSD1306-0.96-OLED"
schX={15}
schY={0}
pinLabels={{
pin1: "GND",
pin2: "VCC",
pin3: "SCL",
pin4: "SDA",
}}
/>

{/* I2C Pull-Up Resistors */}
<resistor name="R1" resistance="4.7k" schX={-5} schY={8} />
<resistor name="R2" resistance="4.7k" schX={5} schY={8} />

{/* Decoupling Capacitors */}
<capacitor name="C1" capacitance="0.1uF" schX={-8} schY={-15} />
<capacitor name="C2" capacitance="0.1uF" schX={10} schY={-15} />

{/* Connections */}
{/* Power Rail (VCC / GND) */}
<trace from=".J1 .pin1" to="net.VCC" />
<trace from=".J1 .pin2" to="net.GND" />

{/* BME280 Power */}
<trace from="net.VCC" to=".U1 .pin1" /> {/* VDD */}
<trace from="net.VCC" to=".U1 .pin3" /> {/* VDDIO */}
<trace from="net.VCC" to=".U1 .pin7" /> {/* CSB high enables I2C mode */}
<trace from=".U1 .pin4" to="net.GND" /> {/* SDO to GND selects address 0x76 */}
<trace from=".U1 .pin2" to="net.GND" />
<trace from=".U1 .pin8" to="net.GND" />

{/* OLED Power */}
<trace from="net.VCC" to=".U2 .pin2" />
<trace from="net.GND" to=".U2 .pin1" />

{/* Decoupling Caps */}
<trace from="net.VCC" to=".C1 .pin1" />
<trace from=".C1 .pin2" to="net.GND" />
<trace from="net.VCC" to=".C2 .pin1" />
<trace from=".C2 .pin2" to="net.GND" />

{/* SCL Bus */}
<trace from=".J1 .pin3" to="net.SCL" />
<trace from="net.SCL" to=".U1 .pin6" />
<trace from="net.SCL" to=".U2 .pin3" />

{/* SDA Bus */}
<trace from=".J1 .pin4" to="net.SDA" />
<trace from="net.SDA" to=".U1 .pin5" />
<trace from="net.SDA" to=".U2 .pin4" />

{/* I2C Pull-Up Connections */}
<trace from="net.VCC" to=".R1 .pin1" />
<trace from=".R1 .pin2" to="net.SCL" />

<trace from="net.VCC" to=".R2 .pin1" />
<trace from=".R2 .pin2" to="net.SDA" />
</board>
)
}
`} />

---

## 💡 Crucial Hardware Design Notes

1. **CSB & SDO Configuration**:
- The BME280 requires the **CSB (Chip Select Bar)** pin to be pulled to **VCC** to enable the **I2C communication interface** (pulling it low selects SPI mode).
- **SDO** is the address select pin. Connecting it to GND sets the 7-bit slave address to `0x76`. Connecting it to VCC sets it to `0x77`.
2. **I2C Bus Pull-Ups**:
- The I2C protocol uses open-drain/open-collector outputs. This means the lines can only pull down to GND; they cannot pull high themselves.
- External pull-up resistors (like **R1** and **R2**) are mandatory to pull SCL and SDA lines up to VCC. Without these, the signals will stay low and the bus will not function.
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