ELM334

Elm Electronics – Circuits for the Hobbyist

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Pin Descriptions

Ordering Information

These integrated circuits are available in either the 300 mil plastic DIP format, or in the 200 mil SOIC surface

mount type of package. To order, add the appropriate suffix to the part number:

300 mil Plastic DIP............................... ELM334P

200 mil SOIC..................................... ELM334SM

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All rights reserved. Copyright ©1999 Elm Electronics.

Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be

given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information

described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these

products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or

systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve

reliability, function, or design.

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 microprocessor, so

an external reset signal is not required. Refer to

the Electrical Characteristics section for further

information.

RLED (pin 2), and GLED (pin 3)

These two pins are for driving a red and a green

LED

through

a

current

limiting

resistance.

Typically the LED used will be a dual type, that

appears white if not energized, red if energized

in one polarity, and green if the polarity is

reversed. Alternatively, two discrete LEDs could

be wired ‘back-to-back’. During powerup, the red

LED will be lit for 0.5sec, followed by the green

for 0.5sec, and then the circuit will alternate

between the two for a further 0.5sec.

PB (pin 4)

A momentary low level signal on this pin will

cause the control output to go high, after

approximately 25msec delay due to the internal

debounce circuitry. If unused, this pin should be

Control (pin 5)

response to a valid low level on pin 4. The

duration of the output will be the same as the

input, to a maximum of 500ms. At this point, the

circuit will assume that the button is ‘stuck’, or

there has been a wiring fault, and it will turn the

output off. The state of the RLED and the GLED

lines is not updated if the circuit thinks that the

pushbutton is being pressed.

ClosedSw (pin 6), and OpenSw (pin 7)

These two inputs are for monitoring the position

of the door. This is normally done by connecting

magnetic reed type switches between each of

mounted at the extreme positions of the door

travel. When fully open, only the OpenSw input

will be at a logic low level (switch closed), and

when fully closed, only the ClosedSw input will

be low. Both switches simultaneously open or

closed will cause the LEDs to alternately flash

red and green as a warning (or as feedback that

the door is moving). Internal circuitry provides a

nominal 0.5sec debounce period on both inputs.

Circuit common is connected to this pin. This is

the most negative point in the circuit.

ELM334DSB