Millivolt Source with Digital Potentiometer
Variable Parameters like voltage, current can be obtained by using a Digital Potentiometer. Microcontrollers or Counters operate FET CMOS Analog Switches. The switches configure resistor networks to adjust circuit performance. It could be a Speed Control of a Motor or Brightness of a Lamp. Volume controls and Tuners also can use this.
Digital Potentiometer - del50003
Here is a Millivolt Source i built for Calibration in the early days. It uses only CMOS Digital and Mixed Chips from Intersil and CD40xx Series.
In this Circuit, digital potentiometer, connect pushbutton switches to fast and slow with one end to +7.5V, when you hold the button down the analog voltage will ramp up-down, fast or slow, this will enable you to make a digitally controlled millivolt source or power supply.
Later i tried a unit with 8748 part of the code in my uC section. This is with Ramp-up and Ramp-down using only two buttons. This works even now, The support below is an HRC Fuse Holder made of Phenolic or Epoxy Resin. The mV Terminations are on Top.
80C39-8749 MCS-48 Examples and code
This was supposed to have Analog in and Analog out. Some parts of the circuit may be in the 80C51 page. This has ramp-up and ramp-down settings for the Increment and Decrement buttons. This helps setting setpoint quickly. There is also debouncing for the pushbutton.
R-2R Digital to Analog Converter, It converts a byte (8 bit) to a analog value. It has 256 levels including zero.
This can be used to convert a byte sent from a microcontroller to a analog value like say 1.51 V. At full scale, when all 8 bits are high calibrate to give 2.55 V then ever bit increment is 0.01V, 10mV steps.