Mushroom Environment Control - Arduino Powered

Step 10 Humidity Calibration

This bit is tricky in that unless you have another humidity reader that you trust you can't be 100% sure that what you are calibrating is correct.

After some investigation I did find that I could get two readings (two is all you need) to calibrate.

First get a a plastic lunch bag and in it put a mug of salt which you have dampened just enough to make it feel like wet sand. Put the humidity reader in with it and wait for about 12 hours. From what I understand the humidity should be at 75% inside the bag.
Read off the serial out on the Arduino to find what value you are getting
Serial.println(humval[4]);
Average this value over a number of readings. Write this value down, this is your X1 val, your Y1 value is 75.

Next go take a shower (take your computer with you), make sure it is a cold morning, after having a shower make sure there is a fine mist and take a number of readings with 
Serial.println(humval[4]);
Average this value and write it down, this is your X2, your Y2 value is 100.
Alternatively the last step can be done using the humidifier inside a large bag with the humidity reader inside it.

Now remember your algebra! Solve these two equations:
Y1 = m*X1 + C
Y2 = m*X2 + C

...and hope that m is as big as possible!

Using the M and C values fill out the portion of the code:

#define HUMIDITY_C 680 
#define HUMIDITY_M 1.6