To monitor temperature with an LM35 and Arduino, connect the sensor’s output to an analog input, convert the board’s ADC reading into volts using the board’s actual reference voltage and resolution, then divide the voltage by 0.010 V/°C. That gives a nominal Celsius reading because the LM35’s output changes by 10 mV per degree Celsius. The exact wiring and attainable accuracy depend on the sensor package and the Arduino board.
What you need to know before wiring an LM35
The LM35 is an analog temperature sensor: it produces a voltage proportional to temperature, with a nominal scale factor of 10 mV/°C. It is not a digital sensor, so the Arduino must measure its output through an analog-to-digital converter (ADC).
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- An LM35 sensor whose exact suffix and package you have identified.
- An Arduino board with a usable analog input. An Uno R3 is the board used in the cited Arduino example; other Arduino boards may use different ADC references or resolutions.
- For a temporary prototype, a breadboard and jumper wires are convenient. The Arduino example documentation lists a breadboard and Uno R3; the breadboard and wires are build choices, not requirements of the sensor itself.
Before connecting anything, check the part marking and use the matching pinout in the LM35 datasheet. TI offers multiple packages and family members with differing ranges; do not assume a generic drawing’s pin order applies to your part. The TI product page identifies the family and its available package information.
How to connect the sensor
For a basic positive-temperature setup, power the sensor as shown in the datasheet, connect its ground to Arduino ground, and connect its output to a valid analog input. The precise pin positions depend on the package and should come from that part’s datasheet.
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- Rated for full −55˚ to +150˚C range
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- Operates from 4 to 30 volts
- Low self-heating, 0.08˚C in still air
- Nonlinearity only ±1⁄4˚C typical
- With the Arduino disconnected from power, identify the LM35 supply, ground, and output pins from the datasheet for your exact package.
- Connect the sensor supply and ground according to the datasheet’s basic application circuit. Connect the sensor ground and Arduino ground together.
- Connect the LM35 output to an analog input, such as A0 if that pin is available on your board.
- Check that the sensor’s supply and output voltage are within the board’s permitted electrical limits before powering the circuit.
A single-supply, direct-output hookup is a straightforward choice for temperatures that produce a positive output voltage. It should not be treated as a circuit for measuring the LM35’s full negative-temperature range.
Convert an Arduino ADC reading to Celsius
The conversion has two stages: convert the ADC count to an estimated input voltage using the selected board’s reference and ADC resolution, then convert that voltage to temperature.
For an ADC that reports counts from 0 through N, where N is the maximum count for the configured resolution:
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- BOJACK High Precision Celsius Temperature Sensor
- Operating Voltage:2.7 V - 5.5 V
- Rated temperature range: -40 °C-+125 °C
- Accuracy: ±2°C
- Scale factor: 10 mV/8°C
Voltage (V) = ADC count × ADC reference voltage (V) ÷ N
Then apply the LM35’s nominal scale factor:
Temperature (°C) = Voltage (V) ÷ 0.010 V/°C
For example, if the ADC calculation produces 0.250 V, the nominal LM35 conversion is 0.250 ÷ 0.010 = 25°C. This example illustrates the sensor’s scale factor; it is not a promised output for a particular Arduino reading.
In code, use the reference voltage and maximum ADC count that match your board and its current ADC configuration. Do not assume every Arduino uses a 5 V reference or the same bit depth. Texas Instruments’ Arduino interface demonstration specifically discusses ADC configuration and reducing conversion error. The TI LM35 Arduino example code is another board-specific reference, not a universal ADC configuration for every Arduino.
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- Specified −40°C to +125°C, operation to +150°C
- Low voltage operation (2.7 V to 5.5 V)
- Stable with large capacitive loads
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Read and display the measurement
Once the wiring and conversion match your board, read the analog input repeatedly and print the calculated Celsius value to the Serial Monitor or send it to a display of your choice. The right output frequency and display depend on the project; the sensor and ADC conversion do not require a particular screen or logging method.
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When checking the result, verify the signal path in order: confirm the sensor pinout, confirm that the analog input is the one connected to the output, confirm the ADC reference and resolution in the calculation, and confirm that the voltage-to-temperature step divides by 0.010 V/°C. A multimeter across the sensor output and ground can help check whether the measured voltage is plausible, but it is optional.
Understand accuracy and sources of error
The sensor specification does not guarantee the accuracy of the assembled Arduino measurement. TI’s product page states 0.5°C ensured accuracy at 25°C and gives a rated LM35 range of −55°C to 150°C, while noting that family variants can differ. Separately, the Rev. H datasheet’s basic application table lists ±0.5°C at 25°C and ±1°C from −55°C to 150°C. These are manufacturer specifications in distinct contexts, not guarantees for every LM35 variant or complete Arduino system.
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- Precision Temperature Measurement: Linear 10mV/°C output (0V at 0°C) with ±0.25°C accuracy at 25°C for reliable data
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- Robust Design: Four 3mm mounting holes secure the module to prototypes or enclosures; compact size 34×22×9mm, 2.6g
- Wide Operating Range: Measures -40°C to +110°C, ideal for environmental monitoring, DIY projects, and industrial prototyping
- Analog Signal Output: Directly interfaces for real-time temperature logging and control systems, suitable for engineers, technicians, factories, individual DIY, electronic enthusiasts, etc
TI also says the LM35 needs no external calibration or trimming to provide typical accuracy of ±¼°C at room temperature and ±¾°C over a full −55°C to 150°C temperature range. That typical-accuracy statement is not the same as the datasheet’s basic-application table limits, and neither accounts for every source of error after installation.
The LM35’s output is relatively small, so ADC step size and reference-voltage accuracy can affect the result. Wiring, electrical noise, sensor placement, thermal contact, and differences between the sensor’s temperature and the object or air being measured can also matter. If closer system-level agreement is important, compare the completed setup with a reliable temperature reference under the conditions in which it will be used.
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Measuring below zero
Do not assume the elementary formula and direct single-supply hookup will measure negative temperatures. The output and circuit arrangement must be suitable for the temperatures being measured, and the Arduino input must stay within its permitted voltage range. TI’s support discussion points to a datasheet circuit that lifts the LM35 ground to support negative readings with a single supply. Follow the circuit and component requirements in the datasheet rather than applying the positive-only hookup unchanged; consult TI’s support discussion for that negative-reading context.
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- Type: Precision Temperature Sensor.Measuremen accuracy +/- 0.25¡ãC
- Operating voltage: DC 4 ~ 30 V;Rated for full ?55? to +150?C
- Model: LM335Z, suitable for remote applications
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- Package: Available in a TO-92 package for easy installatio
Check the exact range and package before building
The LM35 name covers a family, not a single interchangeable package and temperature specification. TI’s product information gives the LM35 a −55°C to 150°C rated range, but family members such as the LM35C have different ratings. Check the suffix, package pinout, supply requirements, and range for the actual device you have before choosing a circuit or interpreting a reading.
For a project limited to ordinary above-zero readings, the basic analog method is simple. Projects that must measure below zero, operate near the sensor’s specified limits, or meet a tighter total error budget need a circuit and measurement plan designed for those conditions.
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