ELM415
Up/Down Interface
Description
Many modern control circuits use the value from
a digital counter to directly determine a setting or
position. Manipulating this value under computer
control is not difficult, but when one has to interface
with a human operator, several other factors must be
considered. Human interfaces often require that the
circuit respond to changes in a setting – up or down,
left or right, clockwise or counterclockwise. These
controls need a simple interface, which the ELM415
provides.
This 8 pin integrated circuit contains all the
timing and logic that is necessary to interface two
pushbuttons to most counter type interfaces. It reads
the position of the switches and translates that into
an appropriate signal for a counter to either
increment or decrement, which in turn controls the
output variable. Logic to filter out contact bounce, to
sense when both keys are pressed simultaneously,
to invert the count output, and to provide continuous
pulses if an input pushbutton stays pressed are all
included.
Features
• Low power CMOS design – typically 1mA at 5V
• Wide supply range – 3.0 to 5.5 volt operation
• Fully debounced switch inputs
• Internal pullup resistors provided
• Protection from simultaneous key presses
• High current drive outputs – up to 25 mA
• User selectable automatic repeat function
• Selectable Count output polarity
Connection Diagram
PDIP and SOIC
(top view)
V
DD
Up/Down
Count
1
2
3
4
8
7
6
5
V
SS
DownSw
UpSw
Repeat
Applications
• Digital audio potentiometer controls
•
•
•
•
Variable voltage or temperature circuits
Motor positioning controls
Single-stepping control circuits
Reset circuits
Invert
Block Diagram
7
V
DD
Debounce
Circuit
reset
DownSw
V
DD
6
Latch
Debounce
Circuit
set
2
Up/Down
UpSw
Logic
Pulse
Generator
Output
Control
3
Count
Repeat
5
4
Invert
ELM415DSA
Elm Electronics – Circuits for the Hobbyist
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