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