dht.py
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''' Original code from https://www.raspberrypi.org/forums/viewtopic.php?t=303606
'''
import utime
import rp2
from rp2 import PIO, asm_pio
from machine import Pin
# --------------------------------------------------- #
# INIT
# --------------------------------------------------- #
# For VCC
dht_pwr = Pin(14, Pin.OUT)
# For data
dht_data = Pin(15, Pin.IN, Pin.PULL_UP)
# Power on
dht_pwr.value(1)
# Create empty state
sm=rp2.StateMachine(1)
# Wait for DHT22 to start up
utime.sleep(2)
# --------------------------------------------------- #
# INIT2
# --------------------------------------------------- #
@asm_pio(set_init=(PIO.OUT_HIGH),autopush=True, push_thresh=8) #output one byte at a time
def DHT22():
#drive output low for at least 20ms
set(pindirs,1) #set pin to output
set(pins,0) #set pin low
set(y,31) #prepare countdown, y*x*100cycles
label ('waity')
set(x,31)
label ('waitx')
nop() [30]
jmp(x_dec,'waitx') #decrement x reg every 100 cycles
jmp(y_dec,'waity') #decrement y reg every time x reaches zero
#begin reading from device
set(pindirs,0) #set pin to input
wait(1,pin,0) #check pin is high before starting
wait(0,pin,0)
wait(1,pin,0)
wait(0,pin,0) #wait for start of data
#read databit
label('readdata')
set(x,21) #reset x register to count down from 20
wait(1,pin,0) #wait for high signal
label('countdown')
jmp(pin,'continue') #if pin still high continue counting
#pin is low before countdown is complete - bit '0' detected
set(y,0)
in_(y, 1) #shift '0' into the isr
jmp('readdata') #read the next bit
label('continue')
jmp(x_dec,'countdown') #decrement x reg and continue counting if x!=0
#pin is still high after countdown complete - bit '1' detected
set(y,1)
in_(y, 1) #shift one bit into the isr
wait(0,pin,0) #wait for low signal (next bit)
jmp('readdata') #read the next bit
# --------------------------------------------------- #
# FUNCTIONS
# --------------------------------------------------- #
def work_dht():
data=[]
total=0
sm.init(DHT22,freq=1600000,set_base=dht_data,in_base=dht_data,jmp_pin=dht_data)
sm.active(1)
for i in range(5): #data should be 40 bits (5 bytes) long
data.append(sm.get()) #read byte
#check checksum (lowest 8 bits of the sum of the first 4 bytes)
for i in range(4):
total=total+data[i]
if((total & 255) == data[4]):
humidity=((data[0]<<8) + data[1])/10.0
temperature=(((data[2] &0x7f) << 8) + data[3]) /10.0
if (data[2] & 0x80) == 0x80:
temperature = -temperature
return [humidity, temperature]
else:
return False