A servo driver board lets a robot control many servo motors without using a separate signal pin for each one. A common example is a PCA9685-style 16-channel board, which receives commands from a microcontroller over I2C and produces many PWM control signals. This matters in robot arms, walkers, pan-tilt cameras, and animatronics where several joints must move smoothly at the same time.
It also keeps wiring organized by separating logic control from high-current servo power.
Key Facts
- A PCA9685-style board commonly provides 16 independent PWM output channels for servo signals.
- The controller communicates with the board using I2C, usually through SDA and SCL pins.
- Servo angle is controlled by pulse width, often about 1.0 ms to 2.0 ms within a 20 ms period.
- PWM frequency for hobby servos is commonly near 50 Hz, so T = 1/f = 1/50 s = 0.020 s.
- The board's logic supply powers the chip, while a separate servo power input supplies motor current.
- Using I2C addresses, multiple driver boards can share the same bus to control more than 16 servos.
Vocabulary
- Servo motor
- A servo motor is a motor with internal control electronics that moves to a commanded position based on a control pulse.
- PWM
- PWM, or pulse width modulation, is a signal method that changes the width of repeated pulses to carry control information.
- I2C
- I2C is a two-wire communication bus that uses a data line and a clock line to let a controller talk to connected devices.
- PCA9685
- The PCA9685 is a PWM driver chip often used to generate many servo control signals from I2C commands.
- Channel
- A channel is one independent output on the driver board that can send a PWM signal to one servo.
Common Mistakes to Avoid
- Powering all servos from the microcontroller 5 V pin is wrong because servo motors can draw high current and may reset or damage the controller.
- Connecting only SDA and SCL but forgetting a shared ground is wrong because the signal voltage needs a common reference between the controller and the driver board.
- Assuming the driver board powers the servos through I2C is wrong because I2C only carries communication signals, not motor power.
- Using the wrong PWM frequency or pulse range is wrong because many hobby servos expect about 50 Hz and may jitter, overheat, or move incorrectly if commanded outside their safe range.
Practice Questions
- 1 A servo driver board controls 12 servos. If each servo can briefly draw 0.8 A, what is the maximum possible current the servo power supply should be prepared to provide?
- 2 A hobby servo uses a 20 ms PWM period. What frequency in hertz does this correspond to, and what percent of the period is a 1.5 ms pulse?
- 3 Explain why a PCA9685-style servo driver can make a robot design easier than connecting every servo signal directly to a microcontroller.