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 208 mil SOIC surface

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

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

208 mil SOIC..................................... ELM334SM

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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 outputs are for driving LEDs (through a

suitable current limiting resistance). Logic ensures

that only one output is active at a time, allowing the

two outputs to drive a single dual type LED (that is

red if energized in one polarity, and green if the

polarity is reversed). During powerup, the red LED

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

0.5 sec, as a LED test.

PB (pin 4)

A momentary low level on this pin will be debounced,

and then used to initiate a 0.5 second output pulse

on pin 5. If unused, it is preferrable to connect this

is an internal pullup resistor).

Control (pin 5)

An active high level pulse will appear at this pin, in

response to a low level on pin 4. Only a single

0.5 sec pulse will be output, regardless of the length

of time that the pin 4 input remains low (as long as it

is greater than the 26 msec debounce time). The

state of the RLED and the GLED lines is not updated

if the pushbutton is being pressed.

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

These two inputs are for monitoring the position of

the door (or other contacts). Since these switches

might be attached to some very simple switch

mechanisms, a long 0.5 sec debounce timer (pickup

and dropout) is used on each input. This allows the

LED outputs to possibly be used with logic circuits,

as well as driving LEDs.

The OpenSw input is not required for circuit

operation. If this input is not used, the LEDs will still

flash alternately when the door is opened, but after

30 seconds, the flashing will stop and the red LED

will light solidly. Please refer to the Circuit Operation

section for more details.

If either pin 6 or pin 7 are not used, it is preferrable to

open-circuited, as they both have internal pullup

resistors).

Circuit common is connected to this pin. This is the

most negative point in the circuit.

ELM334DSC