#!/usr/bin/env python3
# devtimer.py - Temperature Controlled Photographic Darkroom Timer
# Targeted for RaspberryPi
# Copyright (c) 2018 TundraWare Inc.
# Permission Hereby Granted For Unrestricted Personal Or Commercial Use
#####
# Imports
#####
# General Imports
import sys
from threading import Thread
from time import time, sleep
# Hardware Support
from tm1637 import *
import wiringpi
#####
# Constants
#####
DEBUG = True # Debugging switch
# GPIO Ports And Other Hardware Constants
DEFAULT_BRIGHTNESS = 0x0a # Default LED brightness level
TEMP_CLK = 12 # Display connections
TEMP_DIO = 16
TIME_CLK = 21
TIME_DIO = 20
FOOTSW = 6 # GPIO port to read footswitch state
# General Constants
BEEP = 30 # Beep interval
CALIBRATION_OFFSET = 0.003 # Compensate for program overhead in master loop
DEBOUNCE_TIME = 1.5 # In seconds
MINUS = 16 # Index of minus segment table lookup
TEMP_SENTINEL = 999 # Briefly appears at start, if it stays, temp measurement isn't working
# Range of compensated timing
TEMP_LOW=60
TEMP_HIGH=80
# Timing profiles
REALTIME = 0
PAPER = 1
FILM = 2
#####
# Globals
#####
# These get updated by the threads that read the switches and
# thermocouple. On a slow machine like the Pi Zero, we want to avoid
# unnecessary function calls, so we make these globally RW.
# So, shoot me ...
CURRENT_PROFILE = REALTIME
CURRENT_TEMP = TEMP_SENTINEL
# Operating globals
DIM_BY=0 # How much are we currently dimming
FARENHEIGHT=0 # Will be populated with segment pattern for "F"
OUTOFRANGE = False # Flag for compensating profiles when temp is out of range
RUNNING = False # Whether or not to run the timer
#####
# Lookup Table For Compensating Factors
#####
'''
There are 3 tables in the list below. In order:
Realtime - never actually used, just there as a placeholder
Paper
Film
Each contains entires for multiplicative corrections from 60F to 80F.
The profile global above selects which of these tuples to index into
- using the normalized temp global above as the index. We don't
want to use a dictionary here (with profile as the key) because of
the overhead that incurs. Straight tuple indexing should be much
quicker.
WARNING: It takes about 250ms to update the display on a Pi Zero.
So, if the "virtual second" falls at or below this, the
code will be attempting to do updates faster than the
display can handle. So ... the total compensation cannot
reduce the virtual second to less than about 0.300 to be on
the safe side.
'''
compensate = (
(1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000, 1.000),
(1.724, 1.611, 1.505, 1.406, 1.313, 1.227, 1.146, 1.070, 1.000, 0.934, 0.873, 0.815, 0.762, 0.711, 0.665, 0.621, 0.580, 0.542, 0.506, 0.473, 0.442),
(1.445, 1.380, 1.318, 1.259, 1.202, 1.148, 1.096, 1.047, 1.000, 0.955, 0.912, 0.871, 0.832, 0.795, 0.759, 0.725, 0.692, 0.661, 0.631, 0.603, 0.576)
)
#####
# Temperature Measurement Subroutines
#####
'''
This is based on the widely available DS18B20 temperature probe.
It is a 1-wire protocol device that returns temperature directly
degrees C. The dataline must go on the Pi GPIO 4 (pin 7) which
should be pulled up to VCC with a 4.7K resistor.
You have to do several thingsto make this work:
1) Enable 1-wire support in the Pi:
edit /boot/config.txt set: dtoverlay=w1-gpio
reboot
2) Each 1-wire device is connected to the same pin (7)
on the Pi. It distinguishes between them by a uniq
address. You have to find that address *for your specific
device*. You do this by looking at:
ls -l /sys/bus/w1/devices
You'll see the ID of your device there. That needs to
be set in the line below for this code to work with
your device.
'''
DS18B20_ID = "28-0416840ac6ff"
# Read the current temp returned by the probe
def read_probe():
global CURRENT_TEMP
probe = open("/sys/bus/w1/devices/%s/w1_slave" % DS18B20_ID)
temp = float(probe.readlines()[-1].split()[-1].split("=")[-1])/1000 # Parse probe output
temp = int(round((temp * 9/5) +32)) # Convert C-F and round into an integer
# 1-wire interfaces (like the DS18B20 uses) can occasionally
# return wildly wrong results. For this reason, we throw away
# values that have changed more than 10 degrees since the last
# reading, since that's almost certainly noise.
# At startup we want to suppress this check because we have a
# sentinel value set as default for temperature that will briefly
# display an outrageous temperature. If it stays on, it means
# the temperature measurement process isn't working.
if CURRENT_TEMP == TEMP_SENTINEL:
CURRENT_TEMP = temp
elif abs(temp - CURRENT_TEMP) <= 10:
CURRENT_TEMP = temp
probe.close()
# Update and store temperature periodically
def monitor_temps():
global CURRENT_TEMP
while True:
update_temp = Thread(name="Update Temp", target=read_probe).start()
Thread(name="Temp", target=show_temp, args=(temp_led, CURRENT_TEMP)).start()
if DEBUG:
sys.stdout.write("Temp: %sF\n" % CURRENT_TEMP)
sleep(1)
# Display current temperature
# Negative temps are 2 digits, positive temps are 3 digits.
# Suppress leading zeros.
def show_temp(temp_led, temp):
global OUTOFRANGE
minus = hun = ten = one = 0 # Tells display to show nothing
temp_led.brightness=DEFAULT_BRIGHTNESS - DIM_BY
if temp < 0: # The leading digit is a minus sign
minus = temp_led.digit_to_segment[MINUS]
temp = abs(temp)
elif temp > 99: # The 100s position is non-zero
hun = temp // 100
hun = temp_led.digit_to_segment[hun]
if temp > 9: # The 10s position is non-zero
ten =(temp % 100) // 10
ten = temp_led.digit_to_segment[ten]
one = temp_led.digit_to_segment[(temp % 100) % 10]
# If temp is negative, display sign next to most significant digit
if minus:
if not ten:
ten = minus
else:
hun = minus
# Update the temperature LED
temp_led.set_segments([hun, ten, one, FARENHEIGHT])
sleep(0.3)
# If we're in a compensating profile and out of
# temperature range, blink the time display
if OUTOFRANGE:
temp_led.brightness=0
temp_led.set_segments([hun, ten, one, FARENHEIGHT])
#####
# Utility Subroutines
#####
# Beep at the user at fixed intervals
def beep():
print("Beep!")
# Callback when footswitch is pressed
def footsw_pressed():
global RUNNING
# Mask interrupts during debounce window
if time() - footsw_pressed.lastISR >= DEBOUNCE_TIME:
RUNNING = not RUNNING
footsw_pressed.lastISR = time()
if DEBUG:
print("Running State: %s" % RUNNING)
# Check to see if footswitch got pressed
def footsw_monitor():
# We store last interrupt service time as a callback global for debounce
footsw_pressed.lastISR = 0
# Setup the callback
wiringpi.wiringPiISR(FOOTSW, wiringpi.GPIO.INT_EDGE_FALLING, footsw_pressed)
# Run the thread forever waiting for footswitch presses
while True:
sleep(10000)
# Update the display with elapsed time
def show_elapsed(time_led, elapsed):
min = elapsed // 60
sec = elapsed % 60
d0 = time_led.digit_to_segment[min // 10]
d1 = time_led.digit_to_segment[min % 10]
d2 = time_led.digit_to_segment[sec // 10]
d3 = time_led.digit_to_segment[sec % 10]
time_led.set_segments([d0, 0x80 + d1, d2, d3])
#####
# Program entry point
#####
'''
We start a perpetual thread to read the current temperature
and adjust time accordingly
Notice that the actual updating of the display gets run on its own
thread as well. That's because - on a Pi Zero, at least - it takes
over 250ms to do this. We don't want that time added to our timing
loop, so we send it off on a parallel thread, and initiate timing
for the next round in this thread.
'''
if __name__ == "__main__":
# Setup the hardware
wiringpi.wiringPiSetupGpio()
wiringpi.pinMode(FOOTSW, wiringpi.GPIO.INPUT)
wiringpi.pinMode(FOOTSW, wiringpi.GPIO.PUD_UP)
# Dim displays in film mode
DIM_BY = 0
if CURRENT_PROFILE == FILM:
DIM_BY = 2
time_led = TM1637(TIME_CLK, TIME_DIO, DEFAULT_BRIGHTNESS - DIM_BY)
temp_led = TM1637(TEMP_CLK, TEMP_DIO, DEFAULT_BRIGHTNESS - DIM_BY)
# Get segment pattern for "F" - only need to do this once, not on every update
FARENHEIGHT = temp_led.digit_to_segment[0x0f]
# Initialize the time display
Thread(name="InitTimeDisplay", target=show_elapsed, args=[time_led, 0]).start()
# Start measuring temperature
Thread(name="Temperatures", target=monitor_temps).start()
sleep(1) # Wait a bit for the 1st temp measurement to complete
# Start monitoring for footswitch presses
Thread(name="MonitorFootSW", target=footsw_monitor).start()
# Start timing, using the selected profile and measured temperature
elapsed_time = 0
compensation_factor = 1
while True:
# Beep periodically
if not elapsed_time % BEEP:
beep()
if DEBUG:
last = time()
# If we're not running, don't update elapsed time
if not RUNNING:
elapsed_time = 0
# Update the time display
Thread(name="Timer", target=show_elapsed, args=(time_led, elapsed_time)).start()
# For temperatures in-range, look up the compensating factor
OUTOFRANGE = False
if (CURRENT_PROFILE == REALTIME):
compensation_factor = 1 # Realtime requires no compensation
elif TEMP_LOW <= CURRENT_TEMP <= TEMP_HIGH:
compensation_factor = compensate[CURRENT_PROFILE][CURRENT_TEMP-TEMP_LOW]
# Temperature is out of range for our correction table
# This implictly uses the last known compensation factor so we can keep running
else:
OUTOFRANGE = True
sleep(compensation_factor - CALIBRATION_OFFSET)
elapsed_time += 1
elapsed_time %= 6000
if DEBUG:
print("Current Temp: %s Factor: %s Inter-update Time: %s" % (CURRENT_TEMP, compensation_factor, str(time()-last)))
