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PDF ELM401 Data sheet ( Hoja de datos )
| Número de pieza | ELM401 | |
| Descripción | Rotary Encoder Debounce Circuit | |
| Fabricantes | ELM | |
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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.
Applications
• Microcontroller Interfaces
• Monitoring of Encoder Signals
• General Switch Debouncing
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)
VDD 1
A2
B3
Sw 4
8 VSS
7 A out
6 B out
5 Sw out
Block Diagram
ELM401DSB
Rotary
Encoder
VDD
A
2
Debounce
7 A out
Circuit
VDD
B
3
Debounce
6 B out
Circuit
VDD Sw
4
Debounce
5 Sw out
Circuit
Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
1 of 8
Free Datasheet http://www.datasheet4u.com/
1 page  
ELM401
Rotary Encoders
A rotary encoder (sometimes referred to as a
quadrature encoder) is a device that produces digital
(on/off) outputs in response to rotary, or circular,
motion. It is often constructed such that it looks very
much like a potentiometer, or audio volume control
(see the picture of a typical device, at the right).
As the encoder shaft is turned, internal contacts
open and close, creating two waveforms that are
ideally separated in phase by 90 degrees (ie ‘in
quadrature’). Actually, you need to provide external
‘pullup’ resistors and a power supply to create these
waveforms, as the contacts themselves can not do
this. An ideal waveform from a rotary encoder would
look like this:
A
B
Figure 1. Quadrature Waveforms
Due to the 90 degree phase difference, when one
waveform changes, the other is always stable. By
noting the direction of the change and the level of the
other input at that time, you can determine the
direction of motion of the shaft.
Rotary encoders are not ideal, however. Due to
their construction, and variations in shaft speed, the
A typical rotary encoder
waveforms are not perfectly square with the 50% duty
cycles shown. Figure 2 shows a captured trace from a
real rotary encoder that is more representative of what
you will typically find. Note that the two ‘scope
channels (1 and 2) represent the encoder outputs A
and B, respectively. The ch 1 (A) waveform leads the
ch 2 (B) waveform, which usually means that the shaft
is turning in a clockwise direction.
The first rising edge of the channel 2 waveform
shows another problem that occurs with moving
mechanical contacts - multiple pulses due to bounce.
When two contacts meet, the moving one will tend to
bounce, like a ball does when it is dropped on the
floor. Each bounce results in an electrical connection
being made, then broken, which will look like multiple
inputs to a fast electronic circuit. Various mechanical
means are used to reduce the amount of bounce, but it
can never really be eliminated. The following section
discusses how the ELM401 uses electronic means to
remove the bounce.
ELM401DSB
Figure 2. Actual Rotary Encoder waveform
Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
5 of 8
Free Datasheet http://www.datasheet4u.com/
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet ELM401.PDF ] | |
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