External 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.

Hardware Installation

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

LM335 - 4x wiring

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 pinout

Analog pins of Main Connector. Use one			LM335 circuit
PIN N°	SIGNAL	COLOR	SIGNAL
22	ANALOG_3	Brown – Blue	Vout
23	ANALOG_4	White – Red
38	ANALOG_0	Red
39	ANALOG_1	Black
40	ANALOG_2	Violet

Supply voltage of Main connector. Use the corresponding to the autopilot 1x			LM335 circuit
PIN N°	SIGNAL	COLOR	SIGNAL
64	BAT_2	Yellow	V+
67	BAT_1	Blue
68	BAT_0	Red

Ground pins of Main Connector. Use one			LM335 circuit
PIN N°	SIGNAL	COLOR	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

Software Installation

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