Digital Potentiometer
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.The Fast and Slow push switches each operate a Nand Schmitt ocillator. A flip flop Nand pair detect up or down press and sets counters accordingly. All this work is done by CD4093. Now the counter CD4029 can be up-down and binary-decade and even has preset or jam inputs for thumb-wheel or dip-switch interface.
The Cascaded Counters counts the clock you generate by key press to count up-down in binary. The binary digital data is converted to analog by a R-2R resistor network. The opamp is a buffer-non-inverting-amp. The CD4053 Analog switches act like small relays for the R-2R network. they have > 1 tera ohm of OFF resistance and around 100E of ON resistance at +/- 7.5V supply.
Advanced Reading
Datasheets
CD4052BC.pdf
CD4029BC.pdf
CD4093BC.pdf
docs--2184.pdf
bourns.com--r2r.pdf
Information
Digital-to-Analog
maxim Digital Potentiometers
R-2R Ladder
R-2R data converter
