CSC-2700 – (3) Introduction to Robotics

CSC-2700 – (3) Introduction to Robotics Robotics Research Laboratory Louisiana State University

What we learned in last class DC Motor Controller (TB6612FNG) MOSFET-based H-bridges Metal–Oxide–Semiconductor Field-Effect Transistor

H- Bridge

Simple DC-motor control program • int main(void){ • InitHardware(); • // ----------- PWM setting -------------// • ICR3 = 40000u; // input capture registor --> pulse cycle every 40 milli seconds • TCNT3 = 0; // interupt flag registor • // Set the WGM mode & prescalar for oscillating timer ( TCCR3A & TCCR3B : Timer control registors) • TCCR3A = ( 1 << WGM31 ) | ( 0 << WGM30 ) | ( 1 << COM3A1 ) | ( 1 << COM3B1 ) | ( 1 << COM3C1 ); • TCCR3B = ( 1 << WGM33 ) | ( 1 << WGM32 ) | TIMER3_CLOCK_SEL_DIV_8; • DDRE |= (( 1 << 3 ) | ( 1 << 4 ) | ( 1 << 5 )); // I/O control registor (PWM pins as outputs) • MC_HI(STANBY); MC_LO(LEFT0); MC_LO(LEFT1); MC_LO(RIGHT0); MC_LO(RIGHT1); • int speed = 1000; • int delay = 100; • while (1){ • MC_LO(LEFT0);MC_HI(LEFT1); • OCR3A = speed; • ms_spin(delay); • MC_HI(LEFT0);MC_LOW(LEFT1); • speed += 1000; • if (speed > 40000){ • speed = 1000; • } • } • }

Analog to Digital (ADC, A/D or A to D) • Converting a continuous quantity to a discrete time digital representation • Converting an analog voltage to a digital value that can be used by a microcontroller. • There are many sources of analog signals to be measured such as light intensity, temperature, distance, position, etc. • The reverse operation is performed by a digital-to-analog converter (DAC).

Resolution • The number of discrete values it can produce over the range of analog values. • Usually stored electronically in binary form • The numberof discrete values available, or "levels", is a power of two. (ex) 8bits  Range from 0 to 255 • where n is the ADC's resolution in bits V ref-High - V ref-Low Resolution = 2n

ADC in ATMega128 (1) • ATMega128 ADC has 10 bits resolution • What is the range? • Has 8 channels through a multiplexer • 8 pins on PORTF • Need to set PORTF as input without pull-up • How to set this up? • Has own power supply (labeled AVCC) • Allows measuring voltages from 0 to 5 volts with a resolution of 5/1024 volts, or 4.88 mV

ADC in ATMega128 (2) • Can be configured in several different ways • Single-ended� mode : the analog voltages presented on the ADC channels are compared to ground. • There are several selectable voltage references, which determine the range of the ADC conversion. (ex) AVCC • Free-running mode (update continuously) or only one conversion.

Standard Unit of measurement for Electrical current, voltage, and resistance • Interrelation among voltage, current, and resistance E = IR , I = E / R , or R = E / I

Voltage Divider I = E / R 10 mA = 5 V / 500 Ω 0V drop = 10 mA x 0 Ω 5 V R1 = 100 Ω + 4 V 1V drop = 10 mA x 100 Ω 5 V - R2 = 400 Ω 0 V 4V drop = 10 mA x 400 Ω First calculate current ( I ) by using E / R (5 / 500 = 0.01) Then calculate voltage drop at each point based on Ohm’s Law E = I x R (R1 = 0.01 * 100 , R2 = 0.01 * 400)

IR sensor (line detector) & ADC 0V drop = Xi mA x 0 Ω 5 V S1 = 0 ~ 20000 Ω + Connect to ADC X V drop = Xi mA x S1 Ω 5 V - R2 = 1000 Ω X v+ restV drop = Xi mA x 1000Ω 0 V Resistance value of S1(IR sensor) can be changed by sensing

Connecting Sensors

A2D function uint16_t a2d_10( uint8_t Channel ){ // Select the channel in a manner which leaves REFS0 and REFS1 un touched. ADMUX = ( ADMUX & (( 1 << REFS1 ) | ( 1 << REFS0 ))) | Channel; // Start the conversion ADCSR = ADCSR | ( 1 << ADSC ); // Wait for it to complete while ( ADCSR & ( 1 << ADSC )); return ADC; // ADC defined at avr/iom128.h ( special function register: SFR_IO16) } // a2d_10 /home/csc2700/csc2700/40-ADC-01

Send A2D values through UART • Config.h • Set : #define CFG_USE_UART0 1 • Hardware.h • Set : #define UART0_BAUD_RATE 57600 • ADC_test.c • Add : #include "UART.h” • Create file pointer : FILE *u0; // for UART0 • Open u0 • if defined( __AVR_LIBC_VERSION__ ) • u0 = fdevopen( UART0_PutCharStdio, UART0_GetCharStdio ); • #else • u0 = fdevopen( UART0_PutCharStdio, UART0_GetCharStdio, 0 ); • #endif • Send values using fprintf(u0,”your message %d”, variable); /home/csc2700/csc2700/40-ADC-02

Connection configuration for UART • Our programmer has 2 serial port • ttyACM0 : ISP programming port • ttyACM1 : UART serial port • Wire connection • PE0  Yellow wire • PE1  Green wire • GND  Black wire • Open Gtk-term • Set port : /dev/ttyACM1 • Speed : 57600

CSC-2700 – (3) Introduction to Robotics