SunFounder R3, Manual

Page: 283 / 527

SunFounder uno-and-mega-kit
B, short for beta, is a constant. Here it is 4090. Ro is 10k ohms and To is 25 degrees Celsius. The data can be found
in the datasheet of thermistor. Again, the above relation can be transformed into one to evaluate temperature:
T= B/[ ln(R/ 10) + (B/ 298) ] – 273
(So
ln
here means natural logarithm, a logarithm to the base e)
If we use a resistor with fixed resistance as 10k ohms, we can calculate the voltage of the analog input pin A0 with
this formula:
V =10k x 5/(R+10K)
So, this relation can be formed:
R = (5 x 10k /V) - 10k
The voltage of A0 is transformed via A/D adaptor into a digital number a.
a=V x (1024/5)
V=a/205
Then replace V in the relation R = (5 x 10k /V) - 10k with the expression, and we can get this: R=1025 x 10k/a-10k.
Finally replace R in the formula here T= B/[ ln(R/ 10) + (B/ 298) ] – 273, which is formed just now. Then we at last
get the relation for temperature as this:
T =B/[ ln{[ 1025 X 10/a) - 10]/10} (B/298)] – 273
7.12.4 Experimental Procedures
Step 1: Build the circuit.
Step 2: Open the code file.
Step 3:
Select the
Board
and
Port.
Step 4:
Upload the sketch to the board.
7.12. Lesson 12 Thermistor 277