ELM401
Rotary Encoder Debounce Circuit
Description
The ELM401 is an 8 pin integrated circuit that is
used to ‘debounce’ the signals from a mechanical
rotary (quadrature) encoder. 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 ELM401, as this is all
performed within the integrated circuit. The ‘A’ and
‘B’ motion sensing encoder signals are both passed
through a filter then a comparator circuit, and finally
a timer circuit to remove noise and contact bounce,
while the switch input receives standard debounce
processing. The result are three virtually noise-free
signals that are suitable for direct use by an
electronic circuit.
Note that no inversion or manipulation of any
kind is performed on the input signals, other than the
debouncing. If your applications requires decoding of
the signals, you may wish to look at our ELM402 to
ELM408 family of products.
Features
• Low power CMOS design
• Wide supply range – 2.0 to 5.5 volts
• Complete debouncing of the encoder signals
• No external filtering needed
• Includes switch debouncing circuit
• 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
A out
B out
Sw out
Applications
• Microcontroller Interfaces
• Monitoring of Encoder Signals
• General Switch Debouncing
B
Sw
Block Diagram
V
DD
A
2
Debounce
Circuit
7
A out
V
DD
B
3
Debounce
Circuit
6
B out
V
DD
Sw
4
Debounce
Circuit
5
Sw out
Rotary
Encoder
ELM401DSB
Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
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