ELM405 datasheet(7/10 Pages) ELM

7 / 10 page

7 of 10

ELM405DSA

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

ELM405

Output Waveforms

Once the ELM405 has some bounce-free signals

to work with, it can generate outputs based on them.

The logic to decode the motion of an encoder

shaft is not as simple as it would first appear. Some

authorities recommend simply monitoring an input and

when it changes, provide an output based on the level

of the other input. This does not always work, as the

encoder can output multiple signals from only the ‘A’ or

or only the ‘B’ contact if the shaft is moved ever so

slightly when at the detent or at the mid-point position

(between detents). Simply seeing one input change is

not sufficient to say that there is any significant shaft

rotation.

The ELM405 monitors both ‘A’ and ‘B’ transitions,

and determines the outputs based on the sequence in

which the transitions have occurred. This is a better

way to guarantee that the output signals are generated

properly. The internal logic also performs some self-

checking, and monitors for problems such as an output

pulse being initiated before the previous one had

completed, which might occur for some very fast

inputs (the second one will be ignored in this case).

The output of the ELM405 is a series of pulses, as

shown in Figure 4 (representative pulses are enlarged

and shown in Figures 5 and 6). When the encoder is

moving in a clockwise direction, the pulses will be

generated with the U/D output at a high level, while a

counter-clockwise rotation of the shaft results in pulses

generated with the U/D output at a low level. The

direction assumes that the encoder is a standard one,

where the ‘A’ signal leads the ‘B’ for a clockwise

rotation.

Outputs are usually generated each time that one

of the inputs change, so for each full cycle of both of

the inputs, there will be 4 output pulses. This is what is

known as 4x decoding. The other type of decoder that

Figure 4. Output signals (pin 4 = 0V)

Clk

U/D

200 µsec

Figure 5. Up or Clockwise Output

Clk

U/D

200 µsec

Figure 6. Down or Counter-clockwise Output

A Input

B Input

debounce

delay

direction changes

Clk

U/D

ELM405 Fiches technique(PDF) 7 Page - ELM Electronics

ELM405 Fiches technique(HTML) 7 Page - ELM Electronics

Html Pages

1 2 3 4 5 6 7 8 9 10

Fiches technique Télécharger

Lien URL