SubSub page: Resistor DAC

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Introduction:
Connecting a weighted resistor network to binairy outputs creates a DAC. The microprocessor simply does a portwrite command to write the value. 8 resistors would create an 8 bit DAC (256 values). Being short on pins I made a version that needs 6 pins and 6 resistors to get 216 values (close to 8 bit).
This is what I called a "BiTriDAC. It is a combination of 3 binairy (2 positions) and 3 trinairy (3 positions) weighted outputs.

This way you get 2x2x2x3x3x3=216 values.
The trinairy 3 value output is created by using: output-high/input/output-low positions.
For this you need to make 2 tables: one for the output value that you write to the port and one for the data direction register (ddr) for that port.
I made it such that for each value 0-255 I have 2 corresponding table inputs.
Each input value (0-255) is mapped to the 216 table values by adding a softclip curve at both ends. This adds an analog style smooth-clipping to the input data.

This BiTriDAC is used in the MonoVoks2, the Monoladder1 and the PRBSynth1.

Here are the conversion table and the resistor ratios:

More text will be added here