PAGE 100 OF 150 · DISPLAYS & INDICATORS
LED Thermometer Display
A temperature sensor can drive a row of LEDs.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Temperature sensors
- LM35: gives 10 mV per degree C, starting at 0 V.
- TMP36: 10 mV per degree C with a 500 mV offset, so it can show below zero.
- NTC thermistor: resistance falls as it warms, used in a divider.
Reading it
With an LM35 on a 5 V, 10-bit input, temperature in degrees C is about the reading × 0.488. A reading of 51 means roughly 25 degrees.
Display
Light one LED for each 2 degrees, or use an LM3914 with the sensor as its input to make a bar thermometer.
REMEMBER
The sensor gives a voltage; the LEDs show where it falls.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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