Note: added some more photos for clarification.

https://hackaday.com/2022/12/11/a-straightforward-old-fashioned-dac/

Schematic

My assembly consists of two CD4007UBE. CD4007A is given in my book source, which has lower max voltage but is the faster version (30ns vs 20ns; one has to be aware of the general rule not using a faster logic family than necessary because of noise problems). 2R = 100k +/- 1%.

Programming

Generating digital data by means of a Raspberry Pi Pico µC in this project.

MicroPython program for an ad-hoc test (should generate 2.5V): 

from machine import Pin
lsb = Pin(7, Pin.OUT) # bit0, least significant bit
bit1 = Pin(8, Pin.OUT)     
bit2 = Pin(9, Pin.OUT)     
bit3 = Pin(10, Pin.OUT) 
bit4 = Pin(11, Pin.OUT) 
msb = Pin(12, Pin.OUT) # bit5, most significant bit (2^5 = 32)
lsb.high()
bit1.high()      
bit2.high()      
bit3.high()
bit4.low()      
msb.low()

For more sophisticated applications one can deploy the RP2040 Single-cycle IO block (SIO).

C program would look something like:

(...)
void setOutput(int DAC)
{
  *(SIO + 0x014 / 4) = DAC << 7; // we start on GP7
}
(...)
setOutput(15ul);
(...)

Applications

SAR ADC, function generator, etc.

Costs

I paid 50 Cents for each IC, and close to 0 Cents for for the resistors.