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--- comfilepi:controlling_the_lcd_backlight:index [2023/08/30 12:44]
COMFILE Technology [Controlling the LCD Backlight]
+++ comfilepi:controlling_the_lcd_backlight:index [2023/09/19 14:33]
COMFILE Technology [Bash Script Implementation]
@@ Line 3: / Line 3: @@
 The ComfilePi's LCD backlight is connected to GPIO 34.  The backlight can be turned on or off via the command line or via a programming language.
-Please be sure the Raspberry Pi [[https://www.raspberrypi.com/documentation/computers/configuration.html#screen-blanking|Screen Blanking]] feature is disabled to prevent the two from interfering with one another.
 ===== Command Line Interface =====
@@ Line 97: / Line 96: @@
 #include <chrono>
 #include <thread>
+#include <sys/syslog.h>
+#include <pigpiod_if2.h>
 using namespace std;
 using namespace std::chrono;
-#include <pigpiod_if2.h>
 #define PIN 34  // CPi-A/B/F/S
-// #define PIN 44  // CPi-C
+// #define PIN 44 // CPi-C
+void log_info(const char *const message)
+{
+    printf("%s\n", message);
+    syslog(LOG_INFO, "%s", message);
+}
+void log_err(const char *const message)
+{
+    printf("%s\n", message);
+    syslog(LOG_ERR, "%s", message);
+}
 void backlight_on()
 {
     auto instance = pigpio_start(NULL, NULL);
+    if (instance != 0)
+    {
+        log_err("pigpio_start did not return success");
+        return;
+    }
+    auto result = set_mode(instance, PIN, PI_OUTPUT);
+    if (instance != 0)
+    {
+        log_err("set_mode did not return success");
+        return;
+    }
-    set_mode(instance, PIN, PI_OUTPUT);
+    result = gpio_write(instance, PIN, 1);
-    gpio_write(instance, PIN, 1);
+    if (instance != 0)
+    {
+        log_err("gpio_write did not return success");
+        return;
+    }
     pigpio_stop(instance);
 }
 void backlight_off()
 {
     auto instance = pigpio_start(NULL, NULL);
+    if (instance != 0)
+    {
+        log_err("pigpio_start did not return success");
+        return;
+    }
+    auto result = set_mode(instance, PIN, PI_OUTPUT);
+    if (instance != 0)
+    {
+        log_err("set_mode did not return success");
+        return;
+    }
-    set_mode(instance, PIN, PI_OUTPUT);
+    result = gpio_write(instance, PIN, 0);
-    gpio_write(instance, PIN, 0);
+    if (instance != 0)
+    {
+        log_err("gpio_write did not return success");
+        return;
+    }
     pigpio_stop(instance);
 }
+void set_backlight(CARD16 state)
+{
+    switch (state)
+    {
+        case DPMSModeOn:
+            log_info("Turning backlight on");
+            backlight_on();
+            break;
+        case DPMSModeOff:
+            log_info("Turning backlight off");
+            backlight_off();
+            break;
+        default:
+            log_info("Invalid state");
+            break;
+    }
+}
 int main(int argc, char *argv[])
 {
+    openlog("backlight_service", LOG_NDELAY, LOG_USER);
+    log_info("Starting");
     Display *dpy;
     dpy = XOpenDisplay(NULL);
     if (dpy == NULL)
     {
-        fprintf(stderr, "%s:  unable to open display\n", argv[0]);
+        log_err("Unable to open display");
         exit(EXIT_FAILURE);
     }
     BOOL onoff;
+    CARD16 last_state;
     CARD16 state;
+    // Initialize last_state
+    if (!DPMSInfo(dpy, &state, &onoff))
+    {
+        log_err("DPMSInfo returned FALSE");
+    }
+    set_backlight(state);
+    last_state = state;
     while(true)
     {
-        DPMSInfo(dpy, &state, &onoff);
+        if (!DPMSInfo(dpy, &state, &onoff))
-        if (onoff)
         {
-            switch (state)
+            log_err("DPMSInfo returned FALSE");
-            {
+            this_thread::sleep_for(seconds(2));
-                case DPMSModeOn:
+            continue;
-                    backlight_on();
+        }
-                    break;
-                case DPMSModeOff:
+        // If DPMS is not enabled, then display a message
-                    backlight_off();
+        if (!onoff)
-                    break;
+        {
-                default:
+            log_err("DPMSInfo is not enabled");
-                    break;
+            this_thread::sleep_for(seconds(2));
-            }
+            continue;
+        }
+        if (last_state != state)
+        {
+            set_backlight(state);
+            last_state = state;
         }
         this_thread::sleep_for(milliseconds(200));
     }
     XCloseDisplay(dpy);
+    log_info("Exiting");
     return 0;
 }
 </code>
 ==== Compile ====
@@ Line 180: / Line 264: @@
 #!/bin/bash
-export DISPLAY=":0.0"
+PWM_PIN=31
+PIN=34
-PIN=34   # CPi-A/B/F/S
-#PIN=44  # CPi-C
+# Set pins as output
+raspi-gpio set $PWM_PIN op
 raspi-gpio set $PIN op
+# Start with both pins HIGH.  If either of the
+# pins go LOW, the backlight will turn off.
+raspi-gpio set $PWM_PIN dh
+raspi-gpio set $PIN dh
+# Get the current state
+CURRENT_STATUS=$(xset q | grep "Monitor is" | awk '{print $3}')
+LAST_STATUS=$CURRENT_STATUS
+logger -p info -t "backlight_service" -s "Monitor is $CURRENT_STATUS"
 # Loop indefinitely updating backlight in sync with monitor status
@@ Line 191: / Line 286: @@
   # Check the current monitor status
-  current_status=$(xset q | grep "Monitor is" | awk '{print $3}')
+  CURRENT_STATUS=$(xset q | grep "Monitor is" | awk '{print $3}')
+  # Only turn the backlight on/off if the Monitor state has changed
+  if [ "$CURRENT_STATUS" != "$LAST_STATUS" ]; then
+    logger -p info -t "backlight_service" -s "Monitor is $CURRENT_STATUS"
-  # Control backlight pin according to the monitor status
+    # Control backlight pin according to the monitor status
-  if [ "$current_status" = "On" ]; then
+    if [ "$CURRENT_STATUS" = "On" ]; then
-    raspi-gpio set $PIN dh
+      logger -p info -t "backlight_service" -s "Turning Backlight On"
-  else
+      raspi-gpio set $PIN dh
-    raspi-gpio set $PIN dl
+    else
+      logger -p info -t "backlight_service" -s "Turning Backlight Off"
+      raspi-gpio set $PIN dl
+    fi
+    LAST_STATUS=$CURRENT_STATUS
   fi
@@ Line 211: / Line 314: @@
 Add the line ''@xset dpms 0 0 {timeout_in_seconds}'' to the //autostart// file to set the timeout each time the desktop loads.
+Run ''journalctl -t backlight_service -r'' to view the log entries.

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