How to Build a Professional Servo Controller with ATmega328P + AVR C

This is 2nd tutorial on Embedded System design with ATmega328P microcontroller using WinAVR microcontroller which shows how to build Servo Motor controller with ATmega328P, debounce circuit, switches, buffer and power supply circuit. The first tutorial was on controlling DC motor using PWM signal from ATmega328P which you can read in Automated Fan Cooling System: Embedded Project Overview. 

1. Introduction

Here, I will show you how to build a precise servo motor control system using an ATmega328P microcontroller. I will cover everything from power regulation and oscillator stability to interfacing a 16x2 LCD and a servo motor.

2. The Reset Circuit

I will begin by creating the Reset Circuit for the ATmega328P. I am connecting a 10kΩ resistor from the RESET pin to the 5V VCC rail to keep the microcontroller running stably. A momentary push-button is added to pull this pin to ground, allowing us to manually restart the program whenever necessary.

3. LM7805 Voltage Regulation

Next, I will build the power stage using the LM7805 regulator to step down our 12V battery source to a steady 5V.

• At the input, I am using a 100µF electrolytic capacitor to handle large voltage ripples alongside a 0.33µF ceramic capacitor to filter out high-frequency noise.

• At the output, we have a 10µF capacitor for load stability and a 0.1µF capacitor to ensure a clean, noise-free 5V supply.

• These capacitors are essential to prevent regulator oscillation and protect the ATmega328P from power spikes.

4. 16 MHz Crystal Oscillator

To provide a precise heartbeat for our code, we now build the Crystal Oscillator circuit. I am using a 16 MHz external crystal connected across pins 9 and 10. To help the crystal start up and maintain a stable frequency, I am adding two 22pF ceramic load capacitors connected from each crystal leg to ground.

5. Microcontroller Power Connections

With the clock set, I connected the primary power pins of the ATmega328P. I connected VCC and AVCC to our 5V rail, while ensuring GND is tied to the common ground. Connecting AVCC is vital as it powers the internal digital circuitry for several ports, even if the ADC is not in use.

6. 16x2 LCD Interface

Now, I will interface the 16x2 LCD using 4-bit mode to save pins.

• Data lines D4 through D7 connect to pins PC3 through PC0.

• The RS and E pins are tied to PC5 and PC4.

• We also include a 10kΩ potentiometer connected to the VEE pin for manual contrast adjustment.

7. Switch Debouncing and Filtering

For user control, I connected the CW and CCW switches.

• Each switch uses a 4.7kΩ pull-up resistor to keep the signal High when not pressed.

• Between the switches and the 74HC14 Schmitt Trigger inverters, I’ve added an RC filter consisting of a 470kΩ resistor and a 0.1µF capacitor.

• This combination filters out mechanical switch bounce and electrical noise, ensuring the inverter delivers a perfectly clean logic signal to pins PB0 and PB1.

8. Servo Interfacing with LM358

The PWM control signal is generated on pin PB2 (OC1B). I will pass this signal through an LM358 op-amp configured as a voltage-follower buffer. This protects the MCU and ensures the servo receives a strong, consistent control pulse.

9. Decoupling the Servo Power

To prevent system resets caused by motor noise, I am placing a large 470µF electrolytic capacitor directly across the power and ground pins of the servo motor. This acts as a reservoir to handle the high current demands of the servo during movement.

10. Simulation and Testing

Finally, I will start the simulation. On boot-up, the LCD displays a 'Servo Control' welcome message for 2 seconds. Once the main loop starts, you can see the LCD updating the Angle, Percentage, and a visual Bar Graph as I use the switches to rotate the motor.

Watch the following video which shows how I build the circuit from start to finish and the simulation. The simulation shows how the circuit works, how the switches rotate the servo motor. 

Related tutorials:

• Controlling a Hobby Servo Motor with L293D Motor Shield and Arduino
• Servo Motor Control with Motor Shield and Arduino
• Servo Motor control using Simulink and Arduino
• Servo Motor control with ATmega328p
• Servo Control with Johnny-Five and Arduino