ELM401

Elm Electronics – Circuits for the Hobbyist

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Pin Descriptions

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This pin is the positive supply pin, and should always

be the most positive point in the circuit. Internal

circuitry connected to this pin is used to provide

power on reset of the internal logic, so an external

reset signal is not required. Refer to the Electrical

Characteristics section for more information.

A (pin 2)

This input is usually connected to what is normally

known as the ‘A’ signal from a rotary (quadrature)

encoder. An external pullup resistor is required for

the encoder (a typical value is 10 K

Ω), but no

external capacitors are needed (as the internal

debounce circuitry provides the filtering).

B (pin 3)

This input is usually connected to what is normally

known as the ‘B’ signal from a rotary (quadrature)

encoder. An external pullup resistor is required for

the encoder (a typical value is 10 K

Ω), but no

external capacitors are needed (as the internal

debounce circuitry provides the filtering).

Sw (pin 4)

This input may be used to debounce any standard

mechanical contact (from a switch or relay). The

circuitry uses simple set/reset logic to control a timer,

so is not suitable for use with the A or B signal from

a rotary encoder (as those signals continue to

generate sliding noise while the contact is closed).

Sw out (pin 5)

This output is the debounced representation of the

signal that is at pin 4.

B out (pin 6)

This output is the debounced representation of the

signal that is at pin 3.

A out (pin 7)

This output is the debounced representation of the

signal that is at pin 2.

Circuit common is connected to this pin. This is the

most negative point in the circuit.

ELM401DSB