VDD (pin 1)
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
M2 (pin 2), M1 (pin 3) and M0 (pin 4)
The digital levels at these pins determine the mode
of operation, as shown in Table 1 below. Levels are
read whenever the LDR input signal changes, so
www.DataSheetth4aUt.mcoomdes can be changed ‘on the fly’.
frequency filtering so that slowly varying and
pulsating signals will not cause circuit instability. A
logic low level on this pin will be interpreted as the
presence of light, while a logic high results in a dark
input. See the Example Applications section for
Dark (pin 6) and Light (pin 7)
These are the two active high circuit outputs.
Depending on the mode selected, they will either
remain continually active, or provide a 50 msec
pulse output on change from light to dark (Dark
output) or dark to light (Light output).
LDR (pin 5)
This is the voltage sensing input pin. It uses Schmitt
trigger circuitry, and a peak detecting circuit for line
VSS (pin 8)
Circuit common is connected to this pin. This is the
most negative point in the circuit.
M2 M1 M0
Delay on Transition to
Table 1. Modes of Operation
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............................... ELM337P
200 mil SOIC..................................... ELM337SM
All rights reserved. Copyright ©2000 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.
Elm Electronics – Circuits for the Hobbyist
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