Arduino Servo Control with PCA9685: Step-by-Step Tutorial

PWM (Pulse Width Modulation) creates repeating square waves at specific frequencies with adjustable duty cycles. For servo motors, a 50 Hz PWM signal (one pulse every 20ms) controls position: 1.5ms pulse centers the servo at 90°, 0.5ms moves to 0°, and 2.5ms moves to 180°. Servos use a feedback potentiometer system where the controller compares desired position (from PWM) with actual position (from potentiometer voltage) to adjust motor direction until they match.

A servo is an electromechanical device that rotates an axis with high precision, consisting of a DC motor, electronic control circuit, position sensor, gears, and housing. Servos are classified by weight: micro (3-10g), mini (11-25g), standard (25-60g), and large (over 60g). PWM (Pulse Width Modulation) controls servos using two states: high (0.3V) and low (0V). Duty cycle represents the percentage of time the signal remains high, ranging from 0% to 100%. Standard 180-degree servos operate with duty cycles between 2% (0 degrees) and 12% (180 degrees). Frequency is measured in Hertz (typically 50 Hz for servos), and period is the reciprocal (20 milliseconds for 50 Hz).

This section covers servo motor control using PWM (Pulse Width Modulation). Servo motors are used for precise angular control in applications like automatic gates and robotic arms. They have three wires: power (brown/red), ground (black), and signal (green/yellow/orange). The power wire connects to 3.3V or 5V, ground to ground, and signal to a microcontroller pin (e.g., D15). To control servos, you must import both 'pin' and 'PWM' from the machine module. Servo motors use PWM signals with a duty cycle range of 25 to 125, where 25 corresponds to 0 degrees and 125 corresponds to 180 degrees. The duty cycle determines how long the signal is 'on' within each cycle, controlling the servo's position. The duty cycle formula is: duty = min_duty + (angle / 180) * (max_duty - min_duty). For a servo with min_duty=25 and max_duty=125, this converts angles (0-180 degrees) to duty cycle values. A duty cycle of 50 means the motor receives power for 50ms, causing limited movement. A duty cycle of 100 means longer power duration, causing more movement. The duty cycle repeats continuously as the servo moves through different positions.

Servomotors receive position commands through pulse-width modulation (PWM) signals sent every 20 milliseconds (approximately 50 Hz). The pulse width determines the target position: wider pulses move the motor to one extreme, narrower pulses move it to the opposite extreme. Any position between extremes can be achieved by proportionally adjusting pulse width. The signal enters the servo board, is converted to voltage, compared with the potentiometer's feedback voltage using a comparator, and processed by a motor driver with an H-bridge circuit to control rotation direction. The motor rotates until the commanded and actual positions match, then stops.

PWM (Pulse Width Modulation) is used to control servo motors, which differ from DC motors by moving in limited angular ranges (0-180 degrees) rather than continuous rotation. PWM controls servo position by varying the duty cycle. The PWM period is determined by the Auto-Reload Register (ARR), which counts from 0 to ARR before resetting. The duty cycle is calculated as the ratio of high pulses to total pulses in one period, controlled by the Capture Compare Register (CCR).

This video demonstrates how to build and measure a simple DC circuit on a breadboard, covering key concepts including breadboard power and ground rail connections, multimeter range selection for accurate resistance and voltage measurements, series circuit construction where current flows through components sequentially, and parallel circuit configuration where current splits across multiple paths. The instructor emphasizes that proper circuit setup requires a complete closed loop from power source through components back to ground, and that multimeter readings must be interpreted with correct units (ohms, kiloohms, milliamps) based on the selected range.

A breadboard is a prototyping board for building electronic circuits without soldering. It features two main power rails: red for positive voltage and blue/black for negative (ground). These rails run horizontally and are internally connected, allowing power to flow throughout the board. Power sources (5V adapters or batteries) connect through a DC jack with positive and negative terminals. The positive terminal connects to the positive power rail, and the negative to the negative rail. Polarity is critical - connecting backwards damages the circuit. Breadboards can be divided into sections that must be connected using wires (jumpers) to create a unified power system. All power rails become interconnected, creating a distributed power system where any component can connect to any point on the corresponding rail.

A breadboard is a plastic prototyping board with internal metal connections. The top section (positive rail) and bottom section (ground rail) are connected horizontally, while the middle section separates them. A basic electrical circuit requires three components: a power source (battery/power supply), a resistor (to limit current and protect components), and a load (LED or light bulb). The positive rail connects to the positive terminal of the power source, and the ground rail connects to the negative terminal. All points on the positive rail share the same voltage, and all points on the ground rail share the same reference voltage.

This section covers the essential principles of building circuits on breadboards. Key concepts include: (1) Basic circuit components - power source (batteries), load (LEDs), and current-limiting resistors; (2) LED polarity - long leg connects to positive, short leg to negative; (3) Electrical potential - connecting a row to power makes all points share that potential; (4) Ground reference - ground rows have zero potential; (5) Voltage as potential difference between positive and negative rows; (6) Parallel circuit connections where each component receives full supply voltage; (7) Battery configuration - connecting batteries in series increases voltage (two 1.5V batteries = 3V).

A DC circuit is an electrical circuit where current flows in one direction, powered by cells, batteries, or DC supplies. DC circuits consist of basic components: resistors, inductors, capacitors, and voltage/current sources. Circuit analysis relies on Ohm's Law and Kirchhoff's Laws. Key concepts include: Potential difference (work to move unit charge between points, measured in volts), Electric potential (work to bring unit charge from infinity), EMF (potential difference when no current flows), and Electric current (rate of charge flow, measured in amperes). Current flows positive to negative while electrons flow opposite.

I2C uses two lines: SDA (Serial Data) and SCL (Serial Clock). The CPU acts as master, sending commands to slave ICs. Each slave has a unique address (code). When the CPU sends a command, only the matching address responds and performs the action. Pull-up resistors (2.2K ohms) connect SDA and SCL to 1.8V, maintaining signal strength over distance. This allows one CPU to efficiently control multiple ICs through shared communication lines.

I2C is a two-wire serial bus with SDA (data) and SCL (clock) lines using open-collector interfaces with pull-up resistors. Data is valid when SCL is high, changing only when SCL is low. The protocol uses start (SDA falls while SCL high) and stop (SDA rises while SCL high) conditions. Data transfers are byte-oriented (8 bits + ACK bit), with MSB first. The first byte contains the 7-bit slave address plus read/write direction. Slaves acknowledge receipt. I2C supports multi-master arbitration where conflicting masters yield priority to the winner.

I2C communication requires pull-up resistors on both SDA and SCL lines to maintain high state when no device is driving. The start condition occurs when SDA transitions from high to low while SCL is high, signaling the beginning of communication. The master transmits a 7-bit slave address followed by a read/write bit (8th bit). The slave monitors each bit and acknowledges (ACK) by pulling SDA low during the clock low period if the address matches. Data transmission occurs bit by bit, with each bit sampled when SCL transitions from high to low. The master drives SDA during clock low periods while the slave monitors. After each byte, the receiver acknowledges receipt. I2C does not provide built-in data integrity checking. For read operations, the master releases SDA control, allowing the slave to drive it. I2C supports multiple masters through arbitration, where masters compete for bus control by monitoring SDA and comparing intended data with actual bus state. Before initiating communication, the master must check if the bus is available by monitoring both SDA and SCL lines.

During data transmission in I²C, SDA does not change between the rising and falling edges of the clock signal. Data is always read during the middle of the clock pulse. Expressed differently, SDA only transitions when the clock is low. This timing relationship is necessary because an SDA transition when the clock is high would indicate start or stop conditions rather than data changes. This strict timing ensures reliable data sampling by all devices on the bus.

SCL (Serial Clock Line) and SDA (Serial Data Line) traces must have similar resistance values. These traces are part of the I2C communication protocol. If one trace shows 400 ohms and the other shows 500 ohms, this indicates a problem. Both traces should have values close to each other (within a reasonable range) for proper communication.