User Manual

223

The breadboard layout is based on the layout from Lesson 22, so it will simplify

things if you still have this on the breadboard.

There are a few jumper wires near the pot that have been moved slightly on this

layout.

The 10 kΩ resistor and thermistor are all new additions to the board.

Code

After wiring, please open the program in the code folder- Lesson 23 Thermometer

and click UPLOAD to upload the program. See Lesson 2 for details about program

uploading if there are any errors.

Before you can run this, make sure that you have installed the < LiquidCrystal >

library or re-install it, if necessary. Otherwise, your code won't work.

For details about loading the library file, see Lesson 1.

The sketch for this is based on that of lesson 22. Load it up onto your Arduino and

you should find that warming the temperature sensor by putting your finger on it

will increase the temperature reading.

I find it useful to put a comment line above the 'lcd' command.

// BS E D4 D5 D6 D7

LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

This makes things easier if you decide to change which pins you use.

In the 'loop' function there are now two interesting things going on. Firstly we have

to convert the analog from the temperature sensor into an actual temperature, and

secondly we have to work out how to display them.

First of all, let's look at calculating the temperature.

int tempReading = analogRead(tempPin);

double tempK = log(10000.0 * ((1024.0 / tempReading - 1)));

tempK = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * tempK * tempK ))

* tempK );

float tempC = tempK - 273.15;

float tempF = (tempC * 9.0)/ 5.0 + 32.0;

Displaying changing readings on an LCD display can be tricky. The main problem is

that the reading may not always be the same number of digits. So, if the

temperature changed from 101.50 to 99.00 then the extra digit from the old reading

is in danger of being left on the display.

To avoid this, write the whole line of the LCD each time around the loop.