ELM337

Elm Electronics – Circuits for the Hobbyist

< http://www.elmelectronics.com/ >

Connection Diagram

PDIP and SOIC

(top view)

1

2

3

4

8

7

6

5

Light Switch

The ELM337 provides a convenient means to

interface standard photocells or light dependent

resistors (LDRs) to digital logic circuits. It provides

an input comparator with hysteresis, line frequency

filtering, digital delays, and high current output

drivers all within the one 8 pin package.

Three mode setting pins configure the ELM337

for pulse or continuous output and for a delay on

change of from 1 msec to 10 minutes. The transition

threshold is set with a single external resistor,

simplifying designs and minimizing costs.

Applications need not be limited to those

employing photocells, as the Example Applications

section shows. The Schmitt trigger input provides a

convenient way to interface to virtually any input

signal, whether from digital logic or from a slowly

varying analog source. The remainder of the

ELM337 can simply be thought of as a time delay on

pickup and dropout type circuit - very useful for

sequencing processes.

• Low power CMOS design - typically 1mA at 5V

• Operates from 3V to 5.5V

• No external timing elements required

• Low parts count

• Digitally selected delays of up to 10 minutes

• Pulsed or continuous outputs

• Internal line frequency filtering

• High current drive outputs - up to 25 mA

• Automatic lighting controls

• Security light beam monitoring

• Position sensing

• Light controlled counters

• Time delay circuits

LDR

Dark

Light

M2

Description

Applications

Block Diagram

1 of 4

Features

ELM337DSA

M0

M1

LDR

5

7

6

Programmable

Timer

Output

Logic

Light

Dark

4

M0

3

M1

2

M2

Line

Frequency

Detector