Hello Element14 community.
In this forum I will show another play with Omega’s HX94C industrial humidity and temperature sensor with analog output. Today, I will convert analog current output to digital form using Arduino Uno Q.
How to do that is briefly explained in printed manual which come with sensor:
The missing part is “TEMP METER OR RECORDER”. Diagram highlights that it needs some resistor to measure. This is exactly what we need for converting current output to voltage measurable by ADC. Question is what value? The answer is ohm law. We need to map 20mA to 3.3V measured by Arduino UNO Q. Formula is: R = U / I. U is voltage we want to get (3.3V) at maximum current (0.020 A). 3.3 / 0.020 = 165 which means that we need about 165 ohm resistor. I do not have 165 ohm resistor, however I have lot of 330 ohm, so I will use two of them in parallel which result in exactly 165 ohm resistance. Connection is as follows:
In real life:
Now let’s write sketch. Arduino Uno Q support more or less same sketches as older Arduino Unos. Difference is only in using Monitor instead of Serial because it needs utilize interconnection between chips. You can create new app in App Lab by clicking or in terminal:
arduino-app-cli app new analog_humi_temp cd /home/arduino/ArduinoApps/analog_humi_temp
Then you can edit sources using your favourite editor. Sketch is in sketch/sketch.ino:
vim sketch/sketch.ino
Sketch source code:
void setup() {
Monitor.begin(9600);
}
void loop() {
int adcTemp = analogRead(A0);
float voltageTemp = 3.3 * adcTemp / 1024.0;
float currentTemp = 1000 * voltageTemp / 165.0;
float temperature = (currentTemp - 4) * 100 / 16;
int adcHumi = analogRead(A1);
float voltageHumi = 3.3 * adcHumi / 1024.0;
float currentHumi = 1000 * voltageHumi / 165.0;
float humidity = (currentHumi - 4) / 0.16;
Monitor.print("Temperature: ");
Monitor.print(temperature);
Monitor.print("\tHumidity: ");
Monitor.println(humidity);
}
And then you can run it by clicking Run in App lab, or in command line:
arduino-app-cli app start .
And logs you can observe using following command:
arduino-app-cli monitor
It should look as follows:
And that’s it. Outputs from industrial analog sensor are now in hands of modern fully digital Arduino Uno Q. In next part I will look to other sensor kit: Omega’s K-Type Thermocouple.