RESISTANCE_TO_TEMPERATURE

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The RESISTANCE_TO_TEMPERATURE node converts resistance to temperature. The resistance should be a reading from a thermistor in Ohms. Params: unit : select Which unit of temperature to return. Returns: out : Scalar The resulting temperature.

Python Code

from typing import Literal
from flojoy import Scalar, flojoy
from numpy import log


@flojoy
def RESISTANCE_TO_TEMPERATURE(
    default: Scalar,
    unit: Literal["K", "C", "F"] = "K",
    nominal_resistance: float = 1e4,
    nominal_temperature: float = 298.15,
    beta_coefficient: float = 3950,
) -> Scalar:
    """The RESISTANCE_TO_TEMPERATURE node converts resistance to temperature.

    The resistance should be a reading from a thermistor in Ohms.

    Parameters
    ----------
    unit: select
        Which unit of temperature to return.

    Returns
    -------
    Scalar
        The resulting temperature.
    """

    steinhart = log(default.c / nominal_resistance)  # X = ln(R/Ro)
    steinhart /= beta_coefficient  # X / B
    steinhart += 1.0 / (nominal_temperature)  # X + (1/To)
    kelvin = 1.0 / steinhart  # 1 / X
    celsius = kelvin - 273.15
    fahren = celsius * 9 / 5 + 32

    match unit:
        case "K":
            c = kelvin
        case "C":
            c = celsius
        case "F":
            c = fahren

    return Scalar(c=c)

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Example App

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In this example, two measurements are extracted from an Arduino and plotted.

Here is a list of nodes to add:

• OPEN_SERIAL
• SINGLE_MEASUREMENT_SERIAL x2
• VECTOR_INDEXING x4
• LINE x2
• RESISTANCE_TO_TEMPERATURE x2
• APPEND x2
• FEEDBACK x2
• LOOP

Connect the nodes as seen in the example. Next set the number of loops to zero with the LOOP node parameters. Connect the 3 serial nodes to the desired serial device in the node parameters.

The SINGLE_MEASUREMENT_SERIAL should be returning two seperate measurements in the form of a Vector. Therefore, the VECTOR_INDEXING nodes should be set to 0 and 1 to extract the first and second measurements respectively (light intensity and temperature (in resistance)).

The RESISTANCE_TO_TEMPERATURE nodes convert the resistance of the thermistor to temperature.

The Arduino code used is:

#define THERMISTORPIN A2
#define lightsensor A0
#define THERMISTORNOMINAL 10000
#define SERIESRESISTOR 10000


void setup(void) {
  Serial.begin(9600);
}

void loop(void) {
  uint8_t i;
  float reading;

  // convert the value to resistance
  reading = analogRead(THERMISTORPIN);
  reading = 1023 / reading - 1;
  reading = SERIESRESISTOR / reading;

  Serial.print(analogRead(lightsensor));
  Serial.print(",");
  Serial.println(reading);

  delay(40);
}