CSC-2700 – (3) Introduction to Robotics

Robotics Research LaboratoryLouisiana State University

Analog to Digital (ADC, A/D or A to D) 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.

ATMega128 ADC has 10 bits resolution (0~1024) Has 8 channels through a multiplexer 8 pins on PORTF Need to set PORTF as input without pull-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

What we learned in last class

IR sensor (line detector) & ADC

S1 = 0 ~ 20000 Ω

R2 = 1000 Ω -

+5 V

X V drop = Xi mA x S1 Ω

X v+ restV drop = Xi mA x 1000Ω

0V drop = Xi mA x 0 Ω 5 V

Connect to ADC

0 V

Resistance value of S1(IR sensor) can be changed by sensing

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

Translates data between parallel and serial forms

UARTs are commonly used in conjunction with communication standards ex) EIA RS-232, RS-422 or RS-485

Character framing Start bit: logic low Stop bit : logic high ( 1 or 2 bits) Parity bit : optional (even or odd)

Important Setting for Serial UART : Baud Speed , Flow control, Port

Universal Asynchronous Receiver / Transmitter - UART

Minimum required connection RX(yellow),TX(green), and Ground(black)

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 for ttyACM1

9600 for Bluetooth connection

Connection configuration for 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);

Send A2D values through UART

/home/csc2700/csc2700/40-ADC-02

Check the UART buffer first int UART0_IsCharAvailable()

Read a character from UART buffer int UART0_GetChar()

Receiving values from UART

int counter;char tmpChar;While(1)

if ( UART0_IsCharAvailable() ) tmpChar = UART0_GetChar();

if ( tmpChar == ‘s') // start movingelse if ( tmpChar == ‘c') // clear counterelse if ( tmpChar == ‘r’) // report counter number

Make a led0 on when ‘0’ message is received from UART

Make a led0 off when button0 is pressed Make a led1 on when ‘1’ message is

received from UART Make a led1 off when button1 is pressed

Send “!!!good bye!!!” message to UART tx when “bye” message is received from UART rx

Let’s make simple UART program

Make a led0 ON and a motor clockwise spin when ‘4’ message is received from UART

Make a led1 ON and a motor anti-clockwise spin when ‘6’ message is received from UART

Make a led2 ON and speed of the motor increase when ‘8’ message is received from UART

Make a led3 ON and speed of the motor decrease when ‘2’ message is received from UART

Let’s make a motor control program