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Project Notes

#598 LM335 Temperature Sensor

Reading ambient temperature with the LM335 and an Arduino without output display on a Nokia 5110 LCD.

Build

Notes

This circuit uses an LM335 Precision Kelvin Temperature Sensor to measure ambient temperature, and display the result on a Nokia 5110 comptible LCD.

The LM35 is part of a series of easy to use temperature sensors:

Sensor Output Voltage Linearity
LM34 proportional to temperature in Fahrenheit (ºF) 10mV/ºF
LM35 proportional to temperature in Celsius (ºC) 10mV/ºC
LM335 proportional to temperature in Kelvin (ºK) 10mV/ºK

Specifications for the LM335:

  • Directly calibrated in ̊Kelvin
  • 1 ̊C initial accuracy available
  • Operates from 400 μA to 5 mA
  • Less than 1Ω dynamic impedance
  • Easily calibrated
  • LM335 operates from −40 ̊C to +100 ̊C.

NB: I’m testing with an LM335 sourced from element14, and it works fine. I had a number of LM335 components ordered from aliexpress sellers which were all bad (either failed open, or had fixed 0.7B drop regardless of temperature).

Construction

Unlike the LM34 and LM35, the LM335 requires an external pull-up resistor on the anode, sized such that sufficient current can flow and enable the device. I’m using 4.7kΩ

Breadboard

Schematic

Code

See LM335.ino for the sketch.

Reading temperature is straight-forward:

  • LM35 output voltage is read with analog input
  • scaled to 10mV/ºK

Libraries used:

  • u8glib library used for driving the LCD

Testing

with 2.2kΩ current-limiting resistor

with 1st batch - LM335Z chips

acts like open circuit

analog_reading: 1023.00 kelvin: 500.25

with 2nd batch - LM335AZ chips

analog_reading: 142.00 kelvin: 69.20

interesting - same result if reversed. this is reading about 0.7V - 1 diode drop

Credits and References

About LEAP#598 SensorsLM335LCDArduino
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This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.