To test how this might work, and to build a simple demonstration for the CodeClub team, we wrote some Python to use the Astro-Pi's awesome LED matrix to display the latest readings from the humidity sensor.
Adding a battery pack turns this into a useful hand-held humidity sensor (you could easily use it as a thermometer instead with a minor code change).
The code changes the colour of the displayed numbers based on the previous reading. If the humidity has increased then the digits are green, if it has decreased, they're red, and (you guessed it) orange if there has been no change.
Of course the screen only displays two digits so when it gets really hot and steamy...
The code also logs the humidity out to a file, so you can plot humidity against time. Here is 24 hours in our house. The big spike near the start was due to another 'breath test'.
The graph above came from data that was saved every time the display was updated - every half a second - which resulted in a lot of rows! I've now modified the code so that it only writes a result to file once every 30 seconds (the display continues to update every 0.5 seconds). Much more manageable.
Here is the code:
from astro_pi import AstroPi
import time
import logging
from datetime import datetime
ap = AstroPi()
r = [255, 0, 0]
e = [0, 0, 0]
space = [
e,e,e,e,e,e,e,e,
e,e,e,e,e,e,e,e,
]
tmstmp = time.strftime("%Y%m%d-%H%M%S")
logging.basicConfig(format='%(asctime)s %(message)s',filename='humidity'+str(tmstmp)
+'.log',level=logging.DEBUG)
def numToMatrix(num):
# define 1x8 columns that make single digits when combined
num_1_2 = [e,e,r,e,e,e,r,e]
num_1_1 = [e,r,r,r,r,r,r,e]
num_1_0 = [e,e,e,e,e,e,r,e]
num_2_2 = [e,r,e,e,e,r,r,e]
num_2_1 = [e,r,e,e,r,e,r,e]
num_2_0 = [e,r,r,r,e,e,r,e]
num_3_2 = [e,r,e,e,r,e,r,e]
num_3_1 = [e,r,e,e,r,e,r,e]
num_3_0 = [e,r,r,r,r,r,r,e]
num_4_2 = [e,r,r,r,r,e,e,e]
num_4_1 = [e,e,e,e,r,e,e,e]
num_4_0 = [e,r,r,r,r,r,r,e]
num_5_2 = [e,r,r,r,r,e,r,e]
num_5_1 = [e,r,e,e,r,e,r,e]
num_5_0 = [e,r,e,e,r,r,e,e]
num_6_2 = [e,r,r,r,r,r,r,e]
num_6_1 = [e,r,e,e,r,e,r,e]
num_6_0 = [e,r,e,e,r,r,r,e]
num_7_2 = [e,r,e,e,e,e,e,e]
num_7_1 = [e,r,e,e,e,e,e,e]
num_7_0 = [e,r,r,r,r,r,r,e]
num_8_2 = [e,r,r,r,r,r,r,e]
num_8_1 = [e,r,e,e,r,e,r,e]
num_8_0 = [e,r,r,r,r,r,r,e]
num_9_2 = [e,r,r,r,r,e,r,e]
num_9_1 = [e,r,e,e,r,e,r,e]
num_9_0 = [e,r,r,r,r,r,r,e]
num_0_2 = [e,r,r,r,r,r,r,e]
num_0_1 = [e,r,e,e,e,e,r,e]
num_0_0 = [e,r,r,r,r,r,r,e]
# combine columns to make digits
sing_0 = num_0_0 + num_0_1 + num_0_2
sing_1 = num_1_0 + num_1_1 + num_1_2
sing_2 = num_2_0 + num_2_1 + num_2_2
sing_3 = num_3_0 + num_3_1 + num_3_2
sing_4 = num_4_0 + num_4_1 + num_4_2
sing_5 = num_5_0 + num_5_1 + num_5_2
sing_6 = num_6_0 + num_6_1 + num_6_2
sing_7 = num_7_0 + num_7_1 + num_7_2
sing_8 = num_8_0 + num_8_1 + num_8_2
sing_9 = num_9_0 + num_9_1 + num_9_2
# map digits onto appropriate strings
if num == '1':
return sing_1
if num == '2':
return sing_2
if num == '3':
return sing_3
if num == '4':
return sing_4
if num == '5':
return sing_5
if num == '6':
return sing_6
if num == '7':
return sing_7
if num == '8':
return sing_8
if num == '9':
return sing_9
if num == '0':
return sing_0
# set previous humidity value to zero
hum_prev = 0
sec_count = 0
# Main program loop
while True:
# Get humidity from astro-pi
hum_f = ap.get_humidity()
hum_int = int(hum_f)
# test to see if value is higher or lower than previous, and then set led colour appropriately
if sec_count == 60: # only write data every 30 seconds
logging.info(hum_f)
sec_count = 0
if hum_int > hum_prev:
r = [0,255,0] # green if higher
elif hum_int == hum_prev:
r = [255,127,0] # orange if the same
else:
r = [255,0,0] # red if lower
hum_prev = hum_int
hum = str(hum_int) # convert reading to string
image = numToMatrix(hum[1]) + space + numToMatrix(hum[0]) # build image from two digits plus spacer
ap.set_pixels(image)
time.sleep(0.5)
sec_count+=1
