Controlling an AD9851 with an Atmel AtTiny85 (or other)

Following on from my last post, I got something similar working with an ATTiny85. This sample code does a slow sweep from 10Mhz up a bit. It's just a demo, the bit I've been looking for myself and couldn't find was how to just say sendFrequency().

I have lots of ideas for applications of these things, including:

• General purpose VFO with keypad and knob


• Sweep test generator, paired with a digital rf signal measurer for computer plotting filters etc


• Automated antenna analyser with a digital SWR measuring thingy

This code is written in C and uses avrlibc. I'm working on a Mac but it will work the same on Linux or that other OS that was quite popular.

/*
    Control an AD9851 DDS with an ATMega85
*/

#include <avr/io.h>
// Sets up the default speed for delay.h
#define F_CPU 800000UL
#include <util/delay.h>
#include <math.h>   // for pow()

// Pins used to talk to the DDS chip
#define LOAD 4
#define CLOCK 3
#define DATA 0
#define LED 1

#define DDS_CLOCK 180000000UL

#define OUTPORT PORTB
#define OUTPORTDIRECTION DDRB

void sendFrequency(unsigned long frequency);
void byte_out(unsigned char byte);
void outOne();
void outZero();
void bitSetHi(volatile uint8_t *port, int bit);
void bitSetLo(volatile uint8_t *port, int bit);

int main (void)
{
    OUTPORTDIRECTION = _BV(LOAD) | _BV(CLOCK) | _BV(DATA) | _BV(LED);
    unsigned long freq;
    
    // flash an led to show we're alive
    int i;
    for(i = 0; i < 10; i++)
    {
        bitSetHi(&OUTPORT, LED);
        _delay_ms(100);
        bitSetLo(&OUTPORT, LED);
        _delay_ms(100);
    }
    while (1) 
    {
       // Do a frequency sweep in Hz
       for(freq = 10000000; freq < 10001000; freq++)
       {
         sendFrequency(freq);
         _delay_ms(1);
       }
    }
    return 0;
}

void bitSetHi(volatile uint8_t *port, int bit)
{
    *port |= ( 1<<bit );
}

void bitSetLo(volatile uint8_t *port, int bit)
{
    *port &= ~( 1<<bit );
}

void sendFrequency(unsigned long frequency)
{
  unsigned long tuning_word = (frequency * pow(2, 32)) / DDS_CLOCK;
  bitSetLo(&OUTPORT, LOAD); // take load pin low
  int i;
  
  for(i = 0; i < 32; i++)
  {
    if ((tuning_word & 1) == 1)
      outOne();
    else
      outZero();
    tuning_word = tuning_word >> 1;
  }
  byte_out(0x09);

  bitSetHi(&OUTPORT, LOAD); // Take load pin high again
}

void byte_out(unsigned char byte)
{
  int i;

  for (i = 0; i < 8; i++)
  {
    if ((byte & 1) == 1)
      outOne();
    else
      outZero();
    byte = byte >> 1;
  }
}

void outOne()
{
    bitSetLo(&OUTPORT, CLOCK);
    _delay_ms(1);
    bitSetHi(&OUTPORT, DATA);
    _delay_ms(1);
    bitSetHi(&OUTPORT, CLOCK);
    _delay_ms(1);
    bitSetLo(&OUTPORT, DATA);
    _delay_ms(1);
}

void outZero()
{
  bitSetLo(&OUTPORT, CLOCK);
  _delay_ms(1);
  bitSetLo(&OUTPORT, DATA);
  _delay_ms(1);
  bitSetHi(&OUTPORT, CLOCK);
  _delay_ms(1);
}

The AMQRP board has it's own regulator and has a 5V output so I'm powering the ATTiny85 from that power rather than a separate input. Here's a nifty spot reference. Simple enough even for me to build.