347 lines
11 KiB
Markdown
347 lines
11 KiB
Markdown
# Schematic Analysis: Midea AC Controller with BLE Beacon
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## Project Overview
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**Title:** Midea AC Controller with BLE Beacon
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**Date:** 2025-12-28
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**Revision:** 1.0
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**Purpose:** ESP32-based controller for Midea AC units with Bluetooth Low Energy beacon functionality
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---
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## 1. Power Supply System
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### Power Input
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- **Source:** +5V external supply (via J1 connector)
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- **Regulator:** AMS1117-3.3 (U1)
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- Input: +5V (Pin 3 - VI)
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- Output: +3.3V (Pin 2 - VO)
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- Ground: Pin 1 (GND)
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### Power Distribution
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- **+5V Rail:**
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- Powers TXB0104PWR level shifter VCCB (Pin 11)
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- Powers AC connector J1 (Pin 1)
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- Powers +5V power symbols
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- **+3.3V Rail:**
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- Powers ESP32-WROOM-32E VDD (Pin 2)
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- Powers TXB0104PWR level shifter VCCA (Pin 12)
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- Powers TXB0104PWR OE (Pin 10) - always enabled
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- Powers pull-up resistors (R3, R4)
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- Powers LED circuits
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### Decoupling Capacitors
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- **C1:** 5V input filtering (26.67mm, 39.37mm)
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- **C2:** 3.3V output filtering (63.5mm, 39.37mm)
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- **C3:** 3.3V input filtering (38.1mm, 39.37mm)
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- **C4:** 3.3V output filtering (74.93mm, 39.37mm)
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- **C5:** ESP32 VDD decoupling (52.07mm, 81.28mm)
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- **C6:** ESP32 VDD decoupling (52.07mm, 88.9mm)
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**⚠️ Potential Issue:** Missing decoupling capacitors directly on TXB0104PWR power pins (VCCA and VCCB). Datasheet recommends 100nF ceramic capacitors on each power pin.
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---
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## 2. ESP32-WROOM-32E Module (U3)
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### Power Connections
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- **VDD (Pin 2):** +3.3V (with decoupling capacitors C5, C6)
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- **GND (Pin 1, 15, 38, 39):** Ground plane
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### UART Communication
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- **GPIO17 (Pin 25 - TXD0/IO1):** → ESP32_TX label → UART_TX → TXB0104PWR A1 (Pin 1)
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- **GPIO16 (Pin 27 - IO16):** → ESP32_RX label → UART_RX → TXB0104PWR A2 (Pin 2)
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**Note:** The schematic shows GPIO17 as TX and GPIO16 as RX, but these may need to be configured in software depending on which UART peripheral is used.
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### Control Buttons
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- **SW1 (Reset Button):**
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- Connected to EN pin (Pin 3)
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- Pull-up resistor R3 to +3.3V
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- When pressed: EN goes LOW, ESP32 resets
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- **SW2 (Boot Button):**
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- Connected to GPIO0 (Pin 25 - IO0)
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- Pull-up resistor R4 to +3.3V
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- When pressed: GPIO0 goes LOW, ESP32 enters download mode
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### Status LEDs
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- **D1:** Connected via R1 (current limiting resistor)
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- **D2:** Connected via R2 (current limiting resistor)
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- **Note:** LED anodes connect to resistors, cathodes to GND
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### Unused Pins
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Many ESP32 pins are marked as "NC" (No Connect):
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- Pins 17, 18, 19, 20, 21, 22, 32 (NC pins)
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- Pins 4, 5 (SENSOR_VP, SENSOR_VN) - unused
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- Pins 6, 7 (IO34, IO35) - input-only pins, unused
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---
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## 3. Level Shifter: TXB0104PWR (U2)
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### Purpose
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Bidirectional voltage level translation between:
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- **A Port (Low Voltage):** 3.3V side (ESP32)
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- **B Port (High Voltage):** 5V side (AC Controller)
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### Power Connections
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- **VCCA (Pin 12):** +3.3V (low voltage side)
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- **VCCB (Pin 11):** +5V (high voltage side)
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- **GND (Pins 5, 13, 14):** Ground
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- **OE (Pin 10):** +3.3V (always enabled)
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**⚠️ Issue:** OE is connected directly to +3.3V. While this works, datasheet recommends a pulldown resistor for power-up safety. However, since both supplies come from the same source, this is acceptable.
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### Signal Connections
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- **A1 (Pin 1):** ESP32 TX → UART_TX
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- **A2 (Pin 2):** ESP32 RX → UART_RX
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- **B1 (Pin 9):** AC RX → J1 Pin 2
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- **B2 (Pin 8):** AC TX → J1 Pin 3
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### Unused Channels
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- **A3 (Pin 3):** NC
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- **A4 (Pin 4):** NC
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- **B3 (Pin 7):** NC
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- **B4 (Pin 6):** NC
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**Note:** Only 2 of 4 channels are used. This is fine - the IC supports partial channel usage.
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---
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## 4. AC Interface Connector (J1)
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### Connector Type
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- **Type:** Conn_01x04_Pin (4-pin single-row connector)
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- **Footprint:** PinHeader_1x04_P2.00mm_Vertical
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### Pin Assignments
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- **Pin 1:** +5V (power to AC dongle)
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- **Pin 2:** AC_RX (receive from AC, via level shifter B1)
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- **Pin 3:** AC_TX (transmit to AC, via level shifter B2)
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- **Pin 4:** GND (ground)
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### Connection Flow
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```
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ESP32 GPIO17 (TX) → Level Shifter A1 → Level Shifter B2 → J1 Pin 3 (AC_TX)
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ESP32 GPIO16 (RX) ← Level Shifter A2 ← Level Shifter B1 ← J1 Pin 2 (AC_RX)
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```
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---
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## 5. Additional Connector (J2)
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### Connector Type
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- **Type:** Conn_02x04_Counter_Clockwise (8-pin dual-row connector)
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- **Footprint:** PinHeader_2x04_P2.00mm_Vertical
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### Purpose
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**⚠️ Unclear:** J2 is present in the schematic but connections are not fully visible. This may be:
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- Debug/programming connector
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- Additional I/O expansion
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- Reserved for future use
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**Recommendation:** Verify J2 pin assignments and document purpose.
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---
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## 6. Component Summary
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### Active Components
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| Ref | Component | Value | Purpose |
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|-----|-----------|-------|---------|
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| U1 | AMS1117-3.3 | 3.3V LDO | Power regulation |
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| U2 | TXB0104PWR | Level Shifter | 3.3V ↔ 5V translation |
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| U3 | ESP32-WROOM-32E | MCU | Main controller |
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### Passive Components
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| Ref | Component | Value | Purpose |
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|-----|-----------|-------|---------|
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| C1-C6 | Capacitors | Various | Power filtering/decoupling |
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| R1-R4 | Resistors | Various | Current limiting/pull-ups |
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| D1, D2 | LEDs | Status indicators | Visual feedback |
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| SW1, SW2 | Push buttons | Reset/Boot | Control buttons |
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### Connectors
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| Ref | Type | Pins | Purpose |
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|-----|------|------|---------|
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| J1 | 1x04 Pin Header | 4 | AC Controller interface |
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| J2 | 2x04 Pin Header | 8 | Unknown/Reserved |
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---
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## 7. Signal Flow Analysis
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### UART Communication Path
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```
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AC Controller (5V) Level Shifter ESP32 (3.3V)
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───────────────── ───────────── ────────────
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J1 Pin 3 (TX) ────────→ B2 ────────→ A1 ───────→ GPIO17 (TX)
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J1 Pin 2 (RX) ←──────── B1 ←──────── A2 ←─────── GPIO16 (RX)
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```
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### Power Flow
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```
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External 5V → J1 Pin 1 ──┬──→ U1 (AMS1117) ──→ +3.3V ──→ ESP32 VDD
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│
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└──→ U2 VCCB (5V side)
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└──→ +5V rail
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```
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---
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## 8. Design Strengths
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✅ **Proper Power Regulation:** AMS1117-3.3 provides stable 3.3V for ESP32
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✅ **Level Shifting:** TXB0104PWR correctly handles 3.3V ↔ 5V translation
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✅ **Bidirectional Communication:** Automatic direction sensing in level shifter
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✅ **Reset/Boot Controls:** Proper button implementation with pull-ups
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✅ **Decoupling:** Multiple capacitors for power supply filtering
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✅ **Status Indicators:** LEDs for visual feedback
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---
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## 9. Potential Issues & Recommendations
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### ⚠️ Critical Issues
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1. **Missing Decoupling Capacitors on TXB0104PWR**
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- **Issue:** No 100nF capacitors on VCCA (Pin 12) and VCCB (Pin 11)
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- **Impact:** Potential signal integrity issues, noise on power rails
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- **Fix:** Add C7 (100nF) from VCCA to GND, C8 (100nF) from VCCB to GND
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- **Placement:** As close as possible to power pins (<5mm)
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2. **OE Pin Connection**
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- **Current:** OE directly connected to +3.3V
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- **Issue:** No pulldown resistor for power-up safety
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- **Impact:** Minor - may cause brief high-impedance during power-up
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- **Fix (Optional):** Add 10kΩ pulldown resistor from OE to GND
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### ⚠️ Design Considerations
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3. **J2 Connector Purpose**
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- **Issue:** J2 connections not clearly defined
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- **Action:** Document purpose and pin assignments
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4. **ESP32 UART Pin Selection**
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- **Current:** GPIO17 (TX), GPIO16 (RX)
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- **Note:** Verify these are the correct UART peripheral pins
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- **Check:** ESP32-WROOM-32E pinout for UART0/UART1/UART2 assignments
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5. **LED Current Limiting**
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- **Issue:** Resistor values (R1, R2) not specified
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- **Recommendation:** Calculate based on LED forward voltage and desired current
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- **Typical:** 220Ω-1kΩ for 3.3V supply with standard LEDs
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6. **Power Supply Sequencing**
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- **Current:** 5V → 3.3V (via regulator)
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- **Note:** TXB0104PWR requires VCCA ≤ VCCB (satisfied: 3.3V ≤ 5V)
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- **Status:** Acceptable, but ensure proper power-up sequence
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### 💡 Recommendations
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7. **Add Test Points**
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- Consider adding test points for:
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- +5V rail
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- +3.3V rail
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- UART_TX/RX signals
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- GND
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8. **Add Fuse/Protection**
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- Consider adding:
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- Input fuse for +5V protection
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- TVS diodes on UART lines for ESD protection
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9. **Component Values**
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- Document all component values:
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- Capacitor values (C1-C6)
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- Resistor values (R1-R4)
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- LED specifications (D1, D2)
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---
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## 10. PCB Layout Recommendations
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### Critical Placement
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1. **TXB0104PWR Decoupling:**
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- Place 100nF capacitors within 5mm of VCCA and VCCB pins
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- Use short, wide traces
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2. **ESP32 Decoupling:**
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- C5, C6 should be as close as possible to VDD pin
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- Use ground plane for return path
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3. **Level Shifter Placement:**
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- Place TXB0104PWR between ESP32 and J1 connector
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- Minimize trace lengths for UART signals
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4. **Power Traces:**
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- Use adequate trace width for current capacity
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- ESP32 can draw up to 500mA peak
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- Minimum 0.5mm trace width recommended
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5. **Ground Plane:**
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- Use continuous ground plane
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- Connect all GND pins to ground plane
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- Avoid ground loops
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---
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## 11. Testing Checklist
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### Power Supply
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- [ ] Verify +5V input voltage
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- [ ] Verify +3.3V output from regulator (within ±5%)
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- [ ] Check for ripple on power rails
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- [ ] Verify power consumption
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### Level Shifter
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- [ ] Verify VCCA = 3.3V, VCCB = 5V
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- [ ] Test bidirectional signal translation
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- [ ] Verify OE pin is HIGH (enabled)
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- [ ] Check signal integrity on UART lines
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### ESP32
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- [ ] Verify power-on and boot sequence
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- [ ] Test reset button functionality
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- [ ] Test boot button (download mode)
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- [ ] Verify UART communication
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- [ ] Test LED indicators
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### AC Interface
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- [ ] Verify J1 connector pinout
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- [ ] Test UART communication with AC controller
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- [ ] Verify signal levels (3.3V ↔ 5V translation)
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---
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## 12. Bill of Materials (BOM) Summary
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### Required Components
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- 1x ESP32-WROOM-32E module
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- 1x TXB0104PWR (TSSOP-14)
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- 1x AMS1117-3.3 (SOT-223)
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- 6x Capacitors (various values)
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- 4x Resistors (various values)
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- 2x LEDs
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- 2x Push buttons
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- 2x Connectors (J1, J2)
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### Missing Components (Recommended)
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- 2x 100nF capacitors (TXB0104PWR decoupling)
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- 1x 10kΩ resistor (OE pulldown - optional)
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---
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## Conclusion
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The schematic shows a well-designed circuit for an ESP32-based AC controller with proper level shifting for 5V communication. The main areas for improvement are:
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1. **Add decoupling capacitors** on TXB0104PWR power pins
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2. **Document component values** (resistors, capacitors)
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3. **Clarify J2 connector** purpose and connections
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4. **Verify ESP32 UART pin** assignments match software configuration
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Overall, the design is sound and should work correctly with the recommended additions.
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