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 normally not required.
Refer to the Electrical Characteristics section for
R1 (pin 2)
One of the two resistance input pins. A
temperature dependent resistance is usually
connected to this input for heating or under-
www.DataSheette4mUp.ceoramture alarm type applications. When the
value of this resistor is greater than the value of
the resistance connected to pin 3 (for three
successive measurements) the output will be
R2 (pin 3)
The reference resistance is connected to this pin
for heating applications, and the temperature
dependent resistance is connected here for
cooling applications. The other end of this resistor
is connected to the integrating capacitor.
reset (pin 4)
The active low reset input. An internal pullup
resistor is provided for convenience. If unused,
this pin may be connected to VDD or left open.
Cap (pin 5)
Temperature measurements are made by
determining the time to charge and discharge this
integrating capacitor. Pin 5 forces the capacitor to
a known voltage for these measurements though,
resulting in large current flows. To limit these
capacitor currents, and protect the ELM331, a
series resistor must be connected to this pin. The
value of the resistance, and of the capacitance, is
not critical to the measurements.
MIP (pin 6)
This pin provides a logic high level output while
the ELM331 is busy (measurements are in
progress). It is suitable for directly driving an LED
through a current limiting resistor. As a warning,
this output pulses rapidly if either resistor input is
found to be open circuited.
Out (pin 7)
The output pin assumes a logic high state once
the resistance of R1 exceeds that of R2 for three
successive measurement cycles. The output is
maintained until R1 is less than R2 by the
hysteresis amount for an additional three counts.
VSS (pin 8)
Circuit common is connected to this pin. This is
the most negative point in the circuit.
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............................... ELM331P
200 mil SOIC..................................... ELM331SM
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.
Elm Electronics – Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
2 of 4