input devices

For input device I chose an optic rotary encoder from an old hp printer.

I found the data-sheet and it depicted a standard circuit that only included one 1uf capacitor and I realized it was already included on little hp circuit board that supported the encoder. So as I have been reading the Attiny44 data-sheet and I understood that in it I had enough capable pins to read the encoder , drive a motor, read a limit switch and communicate by serial port. As designing a board just for the encoder wouldn't be a challenge in EAGLE (which besides the paying version, has a Light Edition that proved more than adequate), I decided to make a mix of Neal's “hello boards” with a led for debugging, a h-bridge for driving a DC motor, Tx and Rx connection, external button connection and, of course, a connection for the encoder.

At the same time I started trying to get some readings from the encoder with an arduino board. As it has the serial communications pre-embedded, I got both digital an analog reading and I ended up with a simple program that reads 2 digital pins and prints 1 when they are high and 0 when they are low. Then I tried to export it to attiny44.

First I learned that I could charge Neal's C programs through Arduino IDE, which came in handy as I had some problems with the command line from win 8.1 . Then some alterations to the code had to be made for the serial to work. I took Neal's “ hello.ftdi.44.echo.c" programm and combined it with the previous one I had made for Arduino, ending up with this sketch:

#include < avr/io.h >
#include < util/delay.h>
#include < avr/pgmspace.h>

#define output(directions,pin) (directions |= pin) // set port direction for output
#define input(directions,pin) (directions &= (~pin)) // set port direction for input
#define set(port,pin) (port |= pin) // set port pin
#define clear(port,pin) (port &= (~pin)) // clear port pin
#define pin_test(pins,pin) (pins & pin) // test for port pin
#define bit_test(byte,bit) (byte & (1 << bit)) // test for bit set
#define bit_delay_time 8.5 // bit delay for 115200 with overhead
#define bit_delay() _delay_us(bit_delay_time) // RS232 bit delay
#define half_bit_delay() _delay_us(bit_delay_time/2) // RS232 half bit delay
#define char_delay() _delay_ms(10) // char delay

#define serial_port PORTA
#define serial_direction DDRA
#define serial_pins PINA
#define serial_pin_in (1 << PA1)
#define serial_pin_out (1 << PA0)
#define ENCODER_PORT PORTA
#define ENCODER_DIR DDRA
//#define ENCODER1_PIN (1 << PA7)
//#define ENCODER2_PIN (1 << PA6)
const int ENCODER1_PIN = 6; // the number of the pushbutton pin
const int ENCODER2_PIN = 7;
#define max_buffer 25

void get_char(volatile unsigned char *pins, unsigned char pin, char *rxbyte) {
//
// read character into rxbyte on pins pin
// assumes line driver (inverts bits)
//
*rxbyte = 0;
while (pin_test(*pins,pin))
//
// wait for start bit
//
;
//
// delay to middle of first data bit
//
half_bit_delay();
bit_delay();
//
// unrolled loop to read data bits
//
if pin_test(*pins,pin)
*rxbyte |= (1 << 0);
else
*rxbyte |= (0 << 0);
bit_delay();
if pin_test(*pins,pin)
*rxbyte |= (1 << 1);
else
*rxbyte |= (0 << 1);
bit_delay();
if pin_test(*pins,pin)
*rxbyte |= (1 << 2);
else
*rxbyte |= (0 << 2);
bit_delay();
if pin_test(*pins,pin)
*rxbyte |= (1 << 3);
else
*rxbyte |= (0 << 3);
bit_delay();
if pin_test(*pins,pin)
*rxbyte |= (1 << 4);
else
*rxbyte |= (0 << 4);
bit_delay();
if pin_test(*pins,pin)
*rxbyte |= (1 << 5);
else
*rxbyte |= (0 << 5);
bit_delay();
if pin_test(*pins,pin)
*rxbyte |= (1 << 6);
else
*rxbyte |= (0 << 6);
bit_delay();
if pin_test(*pins,pin)
*rxbyte |= (1 << 7);
else
*rxbyte |= (0 << 7);
//
// wait for stop bit
//
bit_delay();
half_bit_delay();
}

void put_char(volatile unsigned char *port, unsigned char pin, char txchar) {
//
// send character in txchar on port pin
// assumes line driver (inverts bits)
//
// start bit
//
clear(*port,pin);
bit_delay();
//
// unrolled loop to write data bits
//
if bit_test(txchar,0)
set(*port,pin);
else
clear(*port,pin);
bit_delay();
if bit_test(txchar,1)
set(*port,pin);
else
clear(*port,pin);
bit_delay();
if bit_test(txchar,2)
set(*port,pin);
else
clear(*port,pin);
bit_delay();
if bit_test(txchar,3)
set(*port,pin);
else
clear(*port,pin);
bit_delay();
if bit_test(txchar,4)
set(*port,pin);
else
clear(*port,pin);
bit_delay();
if bit_test(txchar,5)
set(*port,pin);
else
clear(*port,pin);
bit_delay();
if bit_test(txchar,6)
set(*port,pin);
else
clear(*port,pin);
bit_delay();
if bit_test(txchar,7)
set(*port,pin);
else
clear(*port,pin);
bit_delay();
//
// stop bit
//
set(*port,pin);
bit_delay();
//
// char delay
//
bit_delay();
}
void put_string(volatile unsigned char *port, unsigned char pin, char *str) {
//
// print a null-terminated string
//
static int index;
index = 0;
do {
put_char(port, pin, str[index]);
++index;
} while (str[index] != 0);
}
int main(void) {
//
// main
//
static char chr;
static char buffer[max_buffer] = {0};
static int index;
//
// set clock divider to /1
//
CLKPR = (1 << CLKPCE);
CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
//
// initialize output pins
//
set(serial_port, serial_pin_out);
output(serial_direction, serial_pin_out);
//input(ENCODER_DIR, ENCODER1_PIN);
//input(ENCODER_DIR, ENCODER2_PIN);
//
// main loop
//
index = 0;
while (1) {

if (digitalRead(ENCODER1_PIN) == HIGH){
// right 1:
put_char(&serial_port, serial_pin_out, '1');
}
else {
// right 0:
put_char(&serial_port, serial_pin_out, '0');

if (digitalRead(ENCODER2_PIN) == HIGH){
// right 1:
put_char(&serial_port, serial_pin_out, '1');
}
else {
// right 0:
put_char(&serial_port, serial_pin_out, '0');
}}