LM35 temperature sensor: specs and pinout
Analog temperature sensor in a 3-pin TO-92 package whose output voltage is proportional to the temperature in degrees Celsius.
Specs
| Spec | Value | Source |
|---|---|---|
| Supply voltage +VS | 4 V to 30 V | source 6.3 Recommended Operating Conditions (p.4) |
| Scale factor | Linear, +10 mV per degree C | source 1 Features (p.1) |
| Accuracy at 25 C | Tested limits at 25 C: LM35CA 0.5 C; LM35C 1 C; LM35D 1.5 C (typical 0.4 C for LM35C, 0.8 C for LM35D) | source 6.5 and 6.7 Electrical Characteristics (p.5-7) |
| Operating temperature, TO-92 grades | LM35C/LM35CA: -40 C to 110 C; LM35D: 0 C to 100 C (LM35D cannot read below 0 C). LM35 and LM35A are hermetic TO packages, not TO-92. | source 1 Features / device intro (p.1); 6.3 Recommended Operating Conditions (p.4) |
| Quiescent current | Less than 60 uA | source 1 Features (p.1) |
| Self-heating | 0.08 C in still air | source 1 Features (p.1) |
| Output impedance | 0.1 ohm for 1 mA load | source 1 Features (p.1) |
| Capacitive load without precautions | 50 pF; use a series resistor for heavier loads | source 8.1.1 Capacitive Drive Capability |
Power
| Value | Source | |
|---|---|---|
| Supply | 4 V to 30 V | source 1 Features (p.1); 6.3 (p.4) |
| Current | Less than 60 uA | source 1 Features (p.1); 6.3 (p.4) |
Chip pins
These are the pins of the chip on the module, from the chip datasheet. The module's own header may label or expose them differently.
The TO-92 pinout is from the TI chip datasheet (bottom view). The listing is a bare TO-92 part; check the flat face of your own part against the drawing before powering it.
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| 1 | +VS | 4 V to 30 V | TO-92 (LP package), bottom view: pins read +VS, VOUT, GND from left to right | source 5 Pin Configuration and Functions (p.3) |
| 2 | VOUT | 10 mV per degree C | Temperature sensor analog output | source 5 Pin Configuration and Functions (p.3) |
| 3 | GND | 0 V | Device ground | source 5 Pin Configuration and Functions (p.3) |
Build with it
Project ideas for the LM35 temperature sensor. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- Room thermometer with an LCD: The Uno runs from 5 V, inside the 4 V to 30 V supply range, and its analog input reads the 10 mV per degree output directly.
- Enclosure temperature min/max display: Learning project and display demo, not a safety device. The Uno runs from 5 V, inside the 4 V to 30 V supply range. The LM35 reads 0 C and above in the basic circuit.
- WiFi temperature logger: Power the LM35 from a 5 V pin because it needs at least 4 V; its output (10 mV per degree C, about 250 mV at 25 C) stays inside the ESP32 analog input range. General notes, not from the TI sheet: use an ADC1 pin (ADC2 is unavailable while WiFi is on), and the ESP32 ADC is least accurate at low voltages, so expect limited accuracy.
- Temperature-driven servo vent flap: Learning project: the servo takes its own supply while the LM35 feeds one analog input.
Common mistakes
- Powering it from 3.3 V: the supply range starts at 4 V, so use 5 V and check the output stays inside the ADC range of the board (source: link, 6.3).
- Expecting readings below about 2 C from the basic two-wire circuit: the basic circuit covers 2 C to 150 C; negative temperatures need the full-range circuit with a negative supply (source: link, p.1 application circuits).
- Putting a long cable or a capacitor straight on the output: the output drives only about 50 pF unaided; add a series resistor for heavier loads (source: link, 8.1.1).
Not covered by the official source
- Variant of the TO-92 part on the listing (LM35, LM35C, LM35CA or LM35D) is not stated; accuracy and temperature range depend on grade.
- The listing does not say whether the TO-92 part is LM35C, LM35CA or LM35D; LM35D is looser and cannot read below 0 C.
Sources
- link (TI LM35 datasheet SNIS159H, rev. Dec 2017)