ESP32 Pin Assignments
The following tables list the GPIO pin assignments for the ESP32-WROVER-IE, grouped by function.
Phone Line & Audio Interface
GPIO |
Function |
Description |
|---|---|---|
25 |
PCM_FSYNC |
I2S/PCM word select (frame sync, “LRCLK”) |
5 |
PCM_CLK_OUT |
I2S/PCM bit clock (“BCLK”) |
26 |
PCM_DOUT |
I2S/PCM audio output (to audio interface) |
35 |
PCM_DIN |
I2S/PCM audio input (from audio interface) |
32 |
Off-Hook Detect |
Input: Senses phone off-hook state |
33 |
Ring/Line Status Detect |
Input: Senses ringing or other line status (configurable) |
34 |
Pulse Dial Input |
Input: Detects rotary pulse dial signals (if present) |
39 |
DTMF Input |
Input: From external DTMF decoder IC (optional) |
Bluetooth Module
GPIO |
Function |
Description |
|---|---|---|
16 |
BT Module Reset |
Output: Bluetooth module reset line |
17 |
BT Power Control |
Output: Bluetooth module power enable |
1 |
UART0 TX |
Debug serial output (not for app I/O) |
3 |
UART0 RX |
Debug serial input |
User Interface
GPIO |
Function |
Description |
|---|---|---|
2 |
Status LED |
Output: General status indication |
4 |
User Button |
Input: User pushbutton (pairing, reset, etc.) |
18 |
UI LED |
Output: Additional status LED |
21 |
I2C SDA (optional) |
Data line for I2C display/expander (if used) |
22 |
I2C SCL (optional) |
Clock line for I2C display/expander |
Power and Ground Pins
Power Input:
The Ma Bell Gateway is powered by a regulated 3.3 V DC supply, provided to the ESP32-WROVER-IE module’s 3V3 pin.
Do not exceed 3.3 V on this pin; the ESP32 is not 5V-tolerant.
Power for any peripherals requiring higher voltages (such as ringers or lamps) should be supplied separately and isolated from ESP32 logic. Use opto-isolators or level shifters to interface with the ESP32 where needed.
Ground Reference:
All signals above are referenced to the ESP32’s GND pins.
The ESP32-WROVER-IE module includes multiple GND pads—any may be used to connect the common ground for all circuits, including analog phone interface and Bluetooth module.
Ensure all circuits within the Ma Bell Gateway share a common ground with the ESP32 for reliable operation.
Notes
GPIO6–11 are used internally for flash and must not be used for I/O.
GPIO0, 12, and 15 are used for boot strapping; avoid using them for critical input or output.
GPIO34–39 are input-only and are typically used for detection or monitoring functions.
All features and pin assignments listed here are specific to the Ma Bell Gateway project.