Air Data Sensors

Temperature sensor LM335

LM335 sensor

The LM335 is an analogical temperature sensor that measures temperatures from -40°C to 100°C.

It changes the voltage according to the temperature measured and therefore the connection to the autopilot is performed using the ADC pins.

The following wiring is necessary to connect a sensor to the autopilot:

LM335 sensor - 4x wiring diagram

The LM335 sensor can share voltage supply with the Autopilot 4x. However, the impedance of the resistor R must vary with the voltage; since the sensor requires a forward current between 0.4 and 5 mA to operate. We recommend to use a resistor as high as possible complying with the folllowing equation:

\[\displaystyle \frac{Vin-2.33}{5 \cdot 10^{-3}}<R<\frac{Vin-3.73}{5 \cdot 10^{-4}}\]

Where R is the value of the resistor (ohms) and Vin is the supply voltage (V). The following table shows a list of examples of a tested resistor for each voltage supply. Obtaining an error average of 1.5 °C.

Vin (V)	R (kohms)
6.5	5
12	16
24	37
36	60

The Vout pin has to be connected to an analog input of the Main connector.

Main connector harness pinout

• Users must choose one analog pin to connect:

  Main connector harness			LM335 sensor
  PIN	Signal	Color code	Signal
  22	ANALOG_3	Brown - Blue	Vout
  23	ANALOG_4	White - Red
  38	ANALOG_0	Red
  39	ANALOG_1	Black
  40	ANALOG_2	Violet

• Users must use the supply voltage according to the Autopilot 1x being used:

  Main connector harness			LM335 sensor
  PIN	Signal	Color code	Signal
  64	BAT_2	Yellow	V+
  67	BAT_1	Blue
  68	BAT_0	Red

• Users must choose one ground pin to use:

  Main connector harness			LM335 sensor
  PIN	Signal	Color code	Signal
  9	GND	Black	GND
  18		Gray - Brown
  27		Gray - Green
  33		Green
  41		Gray - Pink
  44		Brown - Green
  47		White - Gray
  48		Gray - Brown
  59		Pink - Green
  63		Green
  65		Gray
  66		Pink

Once connected, the temperature can be monitored in 1x PDI Builder by using the variables ADC0 to ADC4. The wiring explained previously obtains a relationship of Temperature and Vout as follows:

\[T=Vout \cdot 100-273\]

Where T is the measured temperature (in °C, since 273 is substracted in the formula) and Vout the output voltage of the previous circuit.

The integration of this device with Autopilot 4x is explained in the LM335 with Autopilot 4x - Integration examples section of the 1x PDI Builder manual.