Hardware Setup

This guide covers the physical connections and hardware requirements for the PCA9685 chip.

Pin Connections

Basic I2C Connections 

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MCU              PCA9685
โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€
3.3V      โ”€โ”€โ”€โ”€โ”€โ”€ VDD
GND       โ”€โ”€โ”€โ”€โ”€โ”€ GND
SCL       โ”€โ”€โ”€โ”€โ”€โ”€ SCL (with 4.7kฮฉ pull-up to 3.3V)
SDA       โ”€โ”€โ”€โ”€โ”€โ”€ SDA (with 4.7kฮฉ pull-up to 3.3V)

Pin Descriptions

Pin Name Description Required
VDD Power 2.3V to 5.5V power supply (typically 3.3V or 5V) Yes
GND Ground Ground reference Yes
SCL Clock I2C clock line Yes
SDA Data I2C data line Yes
OE Output Enable Active-low output enable (optional) No
A0-A5 Address I2C address selection pins No (for single device)

Output Channels

The PCA9685 provides 16 PWM output channels (OUT0-OUT15). Each channel can drive:

  • LEDs (with current-limiting resistors)
  • Servos (typically 5V servos)
  • Other PWM-controlled devices

Power Requirements

  • Supply Voltage: 2.3V to 5.5V (3.3V or 5V typical)
  • Current Consumption:
    • Active: ~10 mA typical
    • Sleep mode: < 1 ยตA
  • Power Supply: Stable, low-noise supply recommended
  • Decoupling: 100 nF ceramic capacitor close to VDD pin recommended

I2C Configuration

Address Configuration

The PCA9685 I2C address is determined by pins A0-A5:

A5 A4 A3 A2 A1 A0 I2C Address (7-bit)
0 0 0 0 0 0 0x40 (default)
0 0 0 0 0 1 0x41
โ€ฆ โ€ฆ โ€ฆ โ€ฆ โ€ฆ โ€ฆ โ€ฆ
1 1 1 1 1 1 0x7F

Default: All address pins to GND = 0x40 (used in examples)

I2C Bus Configuration

  • Speed: Up to 1 MHz (Fast Mode Plus)
    • Standard Mode: 100 kHz
    • Fast Mode: 400 kHz (most common)
    • Fast Mode Plus: 1 MHz
  • Pull-up Resistors: 4.7 kฮฉ on SCL and SDA (required for I2C)
  • Bus Voltage: Must match VDD (3.3V or 5V)

Physical Layout Recommendations

  • Trace Length: Keep I2C traces short (< 10 cm recommended for high speeds)
  • Ground Plane: Use a ground plane for noise reduction
  • Decoupling: Place 100 nF ceramic capacitor within 1 cm of VDD pin
  • Routing: Route clock and data lines away from noise sources (switching regulators, motors)
  • Multiple Devices: When daisy-chaining, use proper bus termination

Example Wiring Diagram

Single PCA9685 

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                    PCA9685
                    โ”Œโ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”
        3.3V โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”ค VDD     โ”‚
        GND  โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”ค GND     โ”‚
        SCL  โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”ค SCL     โ”‚โ”€โ”€โ”€ 4.7kฮฉ โ”€โ”€โ”€ 3.3V
        SDA  โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”ค SDA     โ”‚โ”€โ”€โ”€ 4.7kฮฉ โ”€โ”€โ”€ 3.3V
                    โ”‚         โ”‚
                    โ”‚ OUT0-15 โ”‚โ”€โ”€โ”€ To LEDs/Servos
                    โ””โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”€โ”˜

Multiple PCA9685 Devices (Daisy Chain) 

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MCU SCL โ”€โ”€โ”ฌโ”€โ”€โ”€ PCA9685 #1 (A0=0, Addr=0x40) SCL
          โ”‚
          โ””โ”€โ”€โ”€ PCA9685 #2 (A0=1, Addr=0x41) SCL

MCU SDA โ”€โ”€โ”ฌโ”€โ”€โ”€ PCA9685 #1 SDA
          โ”‚
          โ””โ”€โ”€โ”€ PCA9685 #2 SDA

Output Enable (OE) Pin

The OE pin is an active-low output enable. When pulled HIGH, all outputs are disabled (high-impedance). When pulled LOW or left floating, outputs are enabled.

Typical Usage:

  • Connect to a GPIO for software control
  • Leave floating if not needed (internal pull-up enables outputs)
  • Use for synchronized startup of multiple devices

Next Steps

  • Verify connections with a multimeter
  • Use an I2C scanner to verify device detection at expected address
  • Proceed to Quick Start to test the connection
  • Review Platform Integration for software setup

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