Embedded Systems Notes

Interfacing Seven Segment Display with 8051

• Segments: Each of the 7 segments labeled from "a" to "g" with an optional decimal point "dp". Illuminating specific segments forms various characters.
• Types of Displays:
  • Common Anode: All segment anodes connected. Each cathode is controlled separately.
  • Common Cathode: All segment cathodes connected. Each anode is controlled separately.
• Numerical Representation: Shows numbers 0-9 and some characters ('A', 'b', 'C', 'd', 'E', 'F', etc.) through segment combinations.
• Applications: Used in digital clocks, microwave ovens, calculators, scoreboards, and meters.

HEX Values for Digits 0-9 on 7-Segment Display

• 0: 0x3F
• 1: 0x06
• 2: 0x5B
• 3: 0x4F
• 4: 0x66
• 5: 0x6D
• 6: 0x7D
• 7: 0x07
• 8: 0x7F
• 9: 0x6F

LCD Pin Details

• Pin 1 (VSS): Ground.
• Pin 2 (VCC): +5V Power supply.
• Pin 3 (VEE): Control contrast.
• Pin 4 (Rs): Register select; 0 for command, 1 for data.
• Pin 5 (R/W): Read/Write; 0 for write, 1 for read.
• Pin 6 (E): Enable.
• Pins 7-14 (D0-D7): 8-bit data bus.
• Pin 15 (LEDA): Anode for backlight LED.
• Pin 16 (LEDK): Cathode for backlight LED.

LCD Command Details

• Commands:
  • 00: Clear display.
  • 02: Return home.
  • 04: Decrement cursor.
  • 06: Increment cursor.
  • 05: Shift display right.
  • 07: Shift display left.
  • 08: Display off, cursor off.
  • 0A: Display off, cursor on.
  • 0C: Display on, cursor off.
  • 0E: Display on, cursor blinking.
  • 10 to 1C: Shift cursor/display positions.
  • 80: Force cursor to the beginning of 1st line.
  • C0: Force cursor to beginning of 2nd line.
  • 38: 2 lines and 5x7 matrix.

Stepper Motor Functionality

• Components: Consists of a stator (four coils) and a rotator (permanent magnet).
• Operation: Energizing coils creates electromagnetic fields that cause rotation. Rotation depends on energizing sequence.
• Stepper Details:
  • Each step is 1.8 degrees if the motor completes 360 degrees in 200 steps.
  • Calculated as: $ext{Step angle} = \frac{360}{200} = 1.8 ext{ degrees}$.

Modes of Stepper Motor

1. Wave Drive: One coil energized at a time.
2. Full Step Drive: Two coils energized simultaneously.
3. Half Step Drive: Alternates energizing one or two coils.

ADC (0804) Overview

• Function: Converts analog signals into digital numbers for microcontroller interpretation.
• Key Pins:
  • Vcc: +5 volts.
  • CLK IN, CLK R: Clocking signals, critical for conversion time (minimum 110 μs).
  • VRef/2: Reference voltage for input range adjustment.
  • CS: Chip select (active low).
  • RD: Read data (active low, outputs the converted data).
  • WR: Starts conversion (active low).
  • INTR: Indicates end of conversion (active low).

DAC (Digital to Analog Converter) Overview

• Purpose: Converts digital values to analog signals for various physical quantities.
• Example DAC: 8-bit DAC0808.
• Formula for Output Voltage: $V<em>{0} = \frac{D imes V</em>{ref}}{2^n}$
  • Where D is the digital input, n is the number of bits.

Calculating Resolution and Accuracy

• Resolution: Smallest change in output for a change of 1 LSB.
• Accuracy: Difference between actual output and expected output.
• Full Scale Output Voltage: Highest output when binary input is at maximum value.

Programs for Waveforms

• Sine Wave Generation: Create a lookup table containing sine values. Use DAC for output.
• Example Table for Sine Wave Values:
  • Angles for 0 to 360 degrees mapped to DAC input values.
  • Use calculation of output voltage: $V_{out} = 5V + (5V imes ext{sin}( heta))$ for precise output tuning.