MMR-70 - cheap radio module

I thought about using the Talkie library for arduino with this module, inspired by #Gas Sensor For Emergency Workers , but it is written for 16 MHz and I would have to deal with timers (again). 16MHz resonators are ordered - although I'm not certain that the atmega32L will work properly at 16MHz and 2.8V. I will look into that, but will also order 8MHz resonators as well and maybe a new LDO for 3.3v? I'm also waiting for some 2x3 pin headers for easier programming via an ISP connector and might make a labeled board... idk.

So with the help of the code from #Portable Trollmaster 3000 I was able to set up the module in no time. It works on the atmega32 (no real surprise here). I've made some little changes to the program - I set the sending power all the way up with the help of the datasheet and also worked on the following function. This should make it easier to set the frequency.

void set_frequency(unsigned long frequency)
{
  unsigned long factor = frequency / 8192;
  unsigned int upper = (uint8_t) (factor >> 8);
  unsigned int lower = (uint8_t) ((factor << 8) >>8);
  
  Wire.beginTransmission(NS731_I2C_addr);
  Wire.write((uint8_t) 0x0a);     
  Wire.write((uint8_t) lower);    // lower 0XEA is 90.0 Mhz 77 / 33 for 108
  Wire.write((uint8_t) upper);    // upper 0X2A Change those values to change the frequency
  Wire.endTransmission(); 
}

updated function, removed not needed type castings etc. (thanks to @al1 )

void set_frequency(unsigned long frequency)
{
  unsigned long factor = frequency / 8192;
  uint8_t upper = factor >> 8;
  uint8_t lower = factor;
  
  Wire.beginTransmission(NS731_I2C_addr);
  Wire.write((uint8_t) 0x0a);     
  Wire.write(lower);    // lower 0XEA is 90.0 Mhz 77 / 33 for 108
  Wire.write(upper);    // upper 0X2A Change those values to change the frequency
  Wire.endTransmission(); 
}

https://instagram.com/p/7LKkQHsYti/

There actually is already a good pinout picture, but I wanted to correct the voltage and be on the safe side when it comes to copyrights - so I fired up inkscape.

int output_pin = 15;
int randNumber;

ISR (TIMER2_COMP_vect)
{
  PORTD ^= ( 1 << PD7 );
}

void setup()
{
  randomSeed(analogRead(0));
  // set LED pin to ouput
  DDRD = ( 1 << PD7 );

//CTC Modus
  TCCR2 = (1 << WGM21);

//Prescaler 64
//3686400 / 64 / 440 = 131
  TCCR2 |= (1 << CS20);
  TCCR2 |= (1 << CS21);
//TCCR2 |= (1 << CS22);

//start with an A
  OCR2 = 131 - 1; 

//Enable Compare Interrupt
  TIMSK |= (1<<OCIE2);

//Enable global Interrupts 
  sei();               
}

void loop()
{
  randNumber = random(256);
  OCR2 = randNumber;
  delay(250);
}