Expand the number of channels. See the shared I2C bus and two ways to power the modules.
Two modules share the I2C bus and 3.3 V logic from the Raspberry Pi. A separate 5 V power supply feeds the servos via V+.
Colour helps you trace a wire. Pin labels determine the connection.
| Signal | From | To |
|---|---|---|
| GND | Raspberry Pi · pin 6 (GND) | PCA1 · GND (left connector) |
| SCL | Raspberry Pi · pin 5 (GPIO3 / SCL1) | PCA1 · SCL (left connector) |
| SDA | Raspberry Pi · pin 3 (GPIO2 / SDA1) | PCA1 · SDA (left connector) |
| VCC | Raspberry Pi · pin 1 (3.3 V) | PCA1 · VCC (left connector) |
| GND | Power supply A · − (GND) | PCA1 · GND terminal |
| V+ | Power supply A · +5 V | PCA1 · V+ terminal |
| GND | PCA1 · GND (right connector) | PCA2 · GND (left connector) |
| SCL | PCA1 · SCL (right connector) | PCA2 · SCL (left connector) |
| SDA | PCA1 · SDA (right connector) | PCA2 · SDA (left connector) |
| VCC | PCA1 · VCC (right connector) | PCA2 · VCC (left connector) |
| V+ | PCA1 · V+ (right connector) | PCA2 · V+ (left connector)Shared power within the group. |
Use physical pins on the 40-pin header: 1 (3.3 V), 3 (GPIO2 / SDA1), 5 (GPIO3 / SCL1) and 6 (GND). A GPIO number is not its position on the header. Check the location of pin 1 on your board. This circuit is not for Raspberry Pi Pico or early boards with a 26-pin header.
Connect module VCC to Raspberry Pi 3.3 V. SDA and SCL may only be pulled up to 3.3 V. Do not connect VCC to V+ or the Pi's 5 V pins. Power servos separately via V+ and connect the grounds. A dedicated power supply powers the Raspberry Pi through its power socket. The PWM signal is at 3.3 V, so the servo must support it.
Run sudo raspi-config, choose Interface Options, then I2C and Yes. A module without address jumpers has address 0x40. In the control software, select bus I2C1 and the module's address. These are electrical wiring instructions; control requires software supporting PCA9685 on Raspberry Pi.
PCA1: 0x40, no jumpers. PCA2: 0x41, A0 bridged. Bridge address pads with power disconnected. Use 7-bit addresses in the configuration.
V+ and GND distribute servo power to both modules. VCC at 3.3 V comes from the Raspberry Pi and powers logic only. At higher currents, run separate wires from the same power supply to both modules' terminals instead of loading the pass-through connectors.
The connectors on both sides of the module are electrically parallel. Connecting modules one after another is not serial data transmission between chips. Keep I2C wires as short as possible. When expanding, check wire capacitance and the combined pull-up resistance on the modules.
Allow for all servos' startup and stall current, voltage drops and the current rating of connectors and tracks on the specific board. Do not power servos from Raspberry Pi 5 V pins. Leave OE unconnected only on modules with a factory-fitted pull-down resistor.
Pinouts and connection rules have been checked against manufacturer documentation.