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App
Notes > DIGITAL
POTENTIOMETERS   GENERAL
ENGINEERING TOPICS

APP 606: Jun 01,
2001

Keywords: digital
potentiometer, digipot, watchdog timer, switch
debouncer, esd protection, digital pots, potentiometers,
push button circuit

Related Parts: MAX5160
MAX6302
MAX6817

Download, PDF Format (216K)

Manually Operated
Digital Potentiometer Doesn't Need a Microprocessor

Operate a digital potentiometer without the use
of a microcontroller. Manually increment up/down with a
simple push-button circuit. Perfect for cost sensitive
applications where manual controls are required to set a
particular level.

Digital potentiometer ICs such as the MAX5160 and MAX5161 are good
replacements for mechanical types. But these ICs are designed to work
with microcontrollers. In this manually operated digital
potentiometer, two pushbuttons control the wiper resistance without
a microcontroller (Figure 1).

Figure 1. This circuit
provides manual up/down control of a digital potentiometer utilizing two
pushbutton switches without using a microcontroller.

To mask the effect of contact bounce in mechanical switches S1 and S2,
a dual switch debouncer (IC1) is used. A microprocessor-supervisor
device configured as an oscillator (IC2) provides a clock signal to
the digital potentiometer. Initially, OUT1, OUT2, and RESET are
high. If S2 is momentarily depressed and released, OUT2 causes the
RESET input of IC2 to go low. When S2 is released, OUT2 and RESET
return high. A 5-bit resistive ladder internal to IC3 (similar to
that of a 5-bit digital-to-analog converter) controls the wiper
position. Therefore, this single cycle of oscillation lowers the
wiper resistance by 1/32 of the total resistance range of the
potentiometer.

IC2 continues to oscillate if S2 is depressed and held. As a result,
the resistance is lowered in a series of steps (Figure 2). Similarly,
depressing S1 increases the potentiometer's resistance. Capacitors C1
and C2 set the frequency of oscillation at approximately 3Hz.

Figure 2. The
resistance-ramp operation is observed by adding an external resistor to
the wiper to form a voltage divider.

A similar version of this article appeared in the April
2, 2001 issue of Electronic Design.

DI361, June 2001

More Information

APP 606: Jun 01,
2001

MAX5160:

QuickView

-- Full
(PDF) Data Sheet (264k)

-- Free
Samples

MAX6302:

QuickView

-- Full
(PDF) Data Sheet (112k)

-- Free
Samples

MAX6817:

QuickView

-- Full
(PDF) Data Sheet (200k)

-- Free
Samples

Download, PDF Format (216K)

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