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Author: Chris Martin
Automatically controls brightness of ASUS VN248 LCD monitor using ambient light level measured by a photosensor.
Responds to user adjustment via buttons; updates internal brightness map to remember user preferences.
Requires connection to photosensor, and wiring harness to monitor button control panel.
GPIO pin usage
Pin 0: read value from photoresistor (LDR)
Pin 2: read voltage applied to monitor power LED to determine on/off state
Pin 8: send 'brightness down' command
Pin 12: send 'brightness up' and 'enter brightness menu' commands
Pin 16: send 'exit brightness menu' command
- Calculate relative change instead of flattening when changing bright_map? Perhaps a better algorithm exists
- Save bright_map to flash memory to remember between reboots
- Don't do anything if monitor is off, detect this with voltage on LED pin?
- If buttons are pressed on micro:bit, enter brightness menu loop. Displays current brightness, push buttons to go up and down. Waits 3 seconds, then saves current value to flash
- How to influence neighboring values? Display brightness should monotonically increase with LDR value. If a user input is saved, any resulting non-monotonic parts of the curve can be "flattened"
- Also, set a threshold for changing brightness. Check more frequently but only change it if LDR value changes by more than a threshold.
- Each press of a button should change brightness for watching feedback
from microbit import *
# Ensure no voltage on pin used for sensing monitor power state
# Build initial brightness map
bright_map = dict()
for i in range(0, 1050, 50):
bright_map[i] = i // 10
def round_down_50(x):
# Round down to nearest multiple of 50; maps LDR values to brightness levels
return x - (x % 50)
def press_button(pin_obj, count=1, press_duration=70):
# Cycles pin_num count number of times, to press corresponding buttons for press_duration milliseconds
# Monitor doesn't recognize all presses if press_duration/sleep values are decreased from default
for i in range(count):
def change_brightness(increment, enter_exit_menu=True):
# Changes monitor brightness by increment steps; negative increment will decrease brightness
if enter_exit_menu:
# Push 'brightness up' button to enter brightness menu
if increment < 0: # Going down
press_button(pin8, abs(increment))
else: # Going up
press_button(pin12, increment)
if enter_exit_menu:
# Push 'menu' button to exit brightness menu
def reset_to_0():
# Resets brightness to 0 when program starts
display.scroll("INITIALIZING", delay=80, wait=False)
press_button(pin12) # Enter brightness menu
press_button(pin8, press_duration=6500) # Hold down button to bring brightness to 0
press_button(pin16) # Exit brightness menu
def get_presses():
# Get presses of both buttons, returns tuple
return button_a.get_presses(), button_b.get_presses()
def update_bright_map(ldr_val, new_bright):
# Update brightness map based on user input
bright_map[round_down_50(ldr_val)] = new_bright
# Iterate through map and adjust so it is monotonically increasing
for possible_ldr_val in range(0, 1050, 50):
if (possible_ldr_val > ldr_val and bright_map[possible_ldr_val] < new_bright) or \
(possible_ldr_val < ldr_val and bright_map[possible_ldr_val] > new_bright):
bright_map[possible_ldr_val] = new_bright
def user_adjust(cur_bright, ldr_val):
# Accept adjustment from user, update map and set new brightness
display.scroll(str(cur_bright), delay=80, wait=False)
new_bright = cur_bright
# Push 'brightness up' button to enter brightness menu
# Loop handles button presses, times out after 3 seconds
last_input_time = running_time()
while True:
a_presses, b_presses = get_presses()
if (a_presses and new_bright > 0) or (b_presses and new_bright < 100):
change = (-5 * a_presses) + (5 * b_presses)
new_bright += change
display.scroll(str(new_bright), delay=80, wait=False)
change_brightness(change, enter_exit_menu=False)
last_input_time = running_time()
elif running_time() > (last_input_time + 3000):
# Exit brightness menu
# If user adjusted brightness, return new value
if new_bright != cur_bright:
update_bright_map(ldr_val, new_bright)
return new_bright
# Main program execution
mon_pwr_state = False
while True:
# Tests monitor power state, only exists when monitor is on and set to known brightness level
while True:
if mon_pwr_state is True:
if pin2.read_analog() > 700:
break # Monitor is still on
mon_pwr_state = False # Go to sleep
elif mon_pwr_state is False:
if pin2.read_analog() > 700:
mon_pwr_state = True # Waking up
# Wait a few seconds for monitor to fully power on, then initialize
cur_bright = 0
# LDR value stored w/ each brightness change to threshold future changes
last_change_ldr_val = None
get_presses() # Clear any button presses accumulated during sleep
sleep(1000) # Monitor still asleep, check again in a second
cur_ldr_val = pin0.read_analog()
a_presses, b_presses = get_presses()
if a_presses or b_presses:
new_bright = user_adjust(cur_bright, cur_ldr_val)
elif last_change_ldr_val is None or abs(cur_ldr_val - last_change_ldr_val) >= 50:
new_bright = bright_map[round_down_50(cur_ldr_val)]
if new_bright != cur_bright:
display.scroll(str(new_bright), wait=False)
change_brightness(new_bright - cur_bright)
if new_bright != cur_bright:
cur_bright = new_bright
last_change_ldr_val = cur_ldr_val