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.
Trimpots and Presets
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.
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.
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.
Potentiometer - AD5242
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
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.
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
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.
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