ELM404
Rotary Decoder - 3 wire 2x Interface
Description
The ELM404 is an 8 pin integrated circuit that is
used to convert the output from a rotary encoder into
three signals (chip select, clock and up/down) that
can be used to control various devices. The low
power CMOS technology used ensures that only a
very small current is required over the entire 2.0 to
5.5 volt operating range.
There is no need for external filtering or
debounce circuits with the ELM404, as this is all
performed within the integrated circuit. After
debouncing the encoder signals, the ELM404
determines the direction of shaft rotation, and then
generates the appropriate outputs. The polarity of
the clock output can be changed at any time to
accommodate different needs.
The ELM404 provides 2x decoding of a rotary
encoder signal. If your application requires 4x
decoding, please see the ELM405 (it is identical to
the ELM404 in every respect, except that it provides
4x decoding).
Features
• Low power CMOS design
• Wide supply range – 2.0 to 5.5 volts
• Complete debouncing of the encoder inputs
• No external filtering needed
• 2x decoding
• Startup delay timer
• High current drive outputs
Connection Diagram
PDIP and SOIC
(top view)
V
DD
A
1
2
3
4
8
7
6
5
V
SS
CS
Clk
U/D
Applications
• Digital audio potentiometer controls
• Variable voltage or temperature circuits
• Positioning controls
• Tuning circuits
B
Clk
Invert
Block Diagram
V
DD
A
2
Debounce
Circuit
Direction
Decoding
Debounce
Circuit
Output
Logic
7
CS
Clk
U/D
6
V
DD
B
3
5
Rotary
Encoder
Clk
Invert
4
ELM404DSA
Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
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