notes_R2R_DAC.md

Playing with a R2R resistor ladder, AKA the quick DAC.

Playing with a 22kO R ladder

An R–2R Ladder is a simple and inexpensive way to perform digital-to-analog conversion, using repetitive arrangements of precise resistor networks in a ladder-like configuration. A string resistor ladder implements the non-repetitive reference network.

Let's try to see if we can do some signal with it!

Playing with it

What does it look like?

Playing with the variant 2 of the code below (increase, bit by bit, over 6 bits)

Limitations

With the variant 2, the quickest signal is at ~5MHz

But when feeding the ladder, it slows... see characteristic time below

Conclusions

Let's try something with the variant 1, feeding the Arduino a translation of one image! It has 28K of flash, let' remove 2k for code, 26kb, using 6-bit accuracy, is 64, leaves 4k points.

Trinket pro codes

Variant 1

The quickest so far

void setup()
 {
  DDRC = 255; // set PORTD (Pins 0-7) to outputs
  PORTC = 0;  // Set all pins LOW
 }
 
void loop() {
   PORTC = B0000000;   
   PORTC = B0000001;   
   PORTC = B0000010;   
   PORTC = B0000011;   
   PORTC = B0000100;   
   PORTC = B0000101;   
   PORTC = B0000110;   
   PORTC = B0000111;
   PORTC = B0001000;   
   PORTC = B0001001;   
   PORTC = B0001010;   
   PORTC = B0001011;   
   PORTC = B0001100;   
   PORTC = B0001101;   
   PORTC = B0001110;   
   PORTC = B0001111;
}

Variant 2

Using autoincrement of PORTC:

void setup()
{
  DDRC = 255; // set PORTD (Pins 0-7) to outputs
  PORTC = 0;  // Set all pins LOW
}
 
void loop() {
   PORTC++;
}