AN219 Datasheet, PDF (1/6 Pages) Microchip Technology – Comparing Digital Potentiometers to Mechanical Potentiometers

AN219
Comparing Digital Potentiometers to Mechanical
Potentiometers
Author: Bonnie C. Baker,
Microchip Technology Inc.
INTRODUCTION
Resistor potentiometers can be found in electronic cir-
cuits across a wide spectrum of applications. Most typ-
ically, they function in a voltage divider configuration in
order to execute various types of tasks, such as offset
or gain adjust. The two types of potentiometers com-
pared in this application note are the mechanical poten-
tiometer (also called a trimmer potentiometer) and the
digital potentiometer. The physical descriptions and cir-
cuit models of these two devices are shown in Figure 1.
Basics of Mechanical Potentiometers
The first type of potentiometer on the market was
mechanical in nature. This type of potentiometer is still
available and adjustments of the wiper are imple-
mented by twisting a knob, moving a slider, or using a
screw driver. Although this method seems awkward,
given the advent of the digital potentiometer, mechani-
cal potentiometers still find their way into various elec-
tronic circuits.
Earlier mechanical potentiometers were built by wrap-
ping a resistive wire around a cylinder. With this con-
struction, the wiper moves from one winding to the
next. As the wiper is moved across the element, there
are discrete steps in resistance. Following this style of
fabrication, the mechanical potentiometer was built
using a resistive thick film that was screened onto a
ceramic substrate. With this construction, the change in
resistance across the element is continuous.
There are a variety of resistive materials that are used
by mechanical potentiometer manufacturers. They
include molded conductive plastic, conductive plastic
film, screened conductive plastic, and cermet. Each
resistive material has its own set of performance char-
acteristics. In this application note the digital potentiom-
eter will only be compared to the more popular cermet
potentiometer. Cermet is a thick film resistive material
that is a mixture of fine particles of ceramic or glass and
precision metals such as silver, platinum, rhodium, or
gold. The wiper of the mechanical potentiometer slides
along the distance on the resistive material providing
an analog resistive output that has an infinite number of
positions across the span of the element.
PA
PW PB
contact
resistance
An example of PCB
mountable Mechanical
potentiometers
Mechanical
Potentiometer
Model
MCP41010
PA
PW PB
wiper
resistance
Digital
Potentiometer
Model
MCP42010
Figure 1: The mechanical potentiometer is constructed so that the user can easily adjust the position of
the wiper (PW) by hand or with a screw driver. The digital potentiometer is manufactured so that the
position of the wiper is adjusted by means of a serial digital code. The circuit representation of the digital
potentiometer and the mechanical potentiometer is fundamentally the same.
 2000 Microchip Technology Inc.
Preliminary
DS00219A-page 1