ELM407

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

Connection Diagram

PDIP and SOIC

(top view)

1

2

3

4

8

7

6

5

Rotary Decoder - 3 wire 4x Interface

The ELM407 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 ELM407, as this is all

performed

within

the

integrated

circuit.

After

debouncing

the

encoder

signals,

the

ELM407

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.

The ELM407 provides 4x decoding of a rotary

encoder signal. If your application requires 2x

decoding, please see the ELM406 (it is identical to

the ELM407 in every respect, except that it provides

2x decoding).

Clk

A

B

Description

• Digital audio potentiometer controls

• Variable voltage or temperature circuits

• Positioning controls

• Tuning circuits

Applications

Block Diagram

1 of 10

• Low power CMOS design

• Wide supply range – 2.0 to 5.5 volts

• Complete debouncing of the encoder inputs

• No external filtering needed

• 4x decoding

• Can generate a write sequence

• Startup delay timer

• High current drive outputs

Features

ELM407DSA

CS

U/D

Write

Enable

B

7

A

Debounce

Circuit

2

CS

5

Direction

Decoding

4

Write

Enable

Output

Logic

3

U/D

Rotary

Encoder

Debounce

Circuit

6

Clk