ELM408
Rotary Decoder - 2 wire Interface
Description
Features
The ELM408 is an 8 pin integrated circuit that is
• Low power CMOS design
used to convert the output from a rotary encoder into
two signals (chip select, 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.
• Wide supply range – 2.0 to 5.5 volts
• Complete debouncing of the encoder inputs
• No external filtering needed
• 2x and 4x decoding
• Can generate a write sequence
• Startup delay timer
There is no need for external filtering or
debounce circuits with the ELM408, as this is all
performed within the integrated circuit. After
debouncing the encoder signals, the ELM408
determines the direction of shaft rotation, and then
generates the appropriate outputs. A write sequence
can also be generated if the Write Enable input is at
a high level when the outputs are generated.
• High current drive outputs
Connection Diagram
PDIP and SOIC
(top view)
The ELM408 provides both 2x and 4x decoding
of a rotary encoder signal. See the Output
Waveforms section for more information.
1
2
3
4
8
7
6
5
VDD
A
VSS
Applications
CS
B
U/D
4x/2x
• Digital audio potentiometer controls
• Variable voltage or temperature circuits
• Positioning controls
Write
Enable
• Tuning circuits
Block Diagram
VDD
A
Debounce
2
Circuit
7
6
CS
Direction
Decoding
Output
Logic
VDD
B
U/D
Debounce
3
Circuit
Rotary
Encoder
4
5
Write
Enable
4x/2x
ELM408DSA
Elm Electronics – Circuits for the Hobbyist
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