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Digital Potentiometer - del50003


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.

Potentiometers Trimpots and Presets

Description. - 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.

MAX5160 Digital Potentiometers - Maxim

I did make a millivolt source with this and it still works after 15 years. Some ideas used in this i got from a magazine elektor and some learning i got from another mag Radio Electronics.
 
Digital
                      Potentiometer


Theory of Operation - The Fast and Slow push switches each operate a Nand Schmitt oscillator. 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.

MilliVolt Source Prototype made in the 80s

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.

MilliVolt Source
                        Prototype made in the 80s

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.

Data sheets and Information.