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+# Announcement Box
+
+Linux box with a loudspeaker and an emergency light to be used for announcements and notifications.
+
+## Hardware
+ * SBC with GPIOs and sound output :: OrangePi Zero with an expansion board
+ * PA system
+   * speaker :: 30W, 4 Ohms horn loudspeaker
+   * sound amplifier :: mono 18W sound amplifier
+   * relay module :: 12V low trigger relay
+ * Warning Light system
+   * warning light :: 12V 10W rotary orange warning light
+   * relay module :: 12V low trigger relay
+ 
+## Software
+ * Operating System - Linux :: Armbian Bullseye for the OrangePi Zero
+ * PA System
+   * Voice Synthesizer :: Festival / ESpeak
+
+## Implementation Notes
+
+### Armbian + OrangePi Zero Installation
+
+#### Enable analog soundcard
+```
+sudo armbian-config
+# System > Hardware > [*] analog-codec
+```
+
+#### Software Dependencies
+##### OS Packages
+```bash
+apt install mplayer espeak-ng
+```
+
+##### GPIO toolkit
+```bash
+# upstream:
+#git clone https://github.com/orangepi-xunlong/wiringOP
+# enhanced:
+git clone https://github.com/Dejvino/wiringOP
+cd wiringOP
+./build clean
+./build
+```
+
+#### Initialize GPIOs
+```bash
+# System Activity Indicator
+PIN_SALIGHT=11
+gpio mode $PIN_SALIGHT output
+
+# Emergency Light system
+PIN_ELIGHT=7
+gpio mode $PIN_ELIGHT output
+
+# PA system
+PIN_PASOUND=5
+gpio mode $PIN_PASOUND output
+```
+
+### PA System
+#### Text to Speech
+```bash
+## Festival
+# reading
+...
+# to file
+text2wave text.txt > wave.wav
+
+## ESpeak
+# voices:
+ls /usr/lib/arm-linux-gnueabihf/espeak-data/voices/
+# reading
+espeak -f text.txt -p 40 -s 160 -v "en-us"
+# to file
+espeak -f text.txt -p 40 -s 160 -k15 -g 1 -w wave.wav
+# using SSML (e.g.: https://www.xml.com/pub/a/2004/10/20/ssml.html)
+espeak -f ssml.txt -m
+```
+
+#### Converting into a low-quality broadcast audio
+```bash
+sox infile.wav outfile.wav downsample echo 0.5 1 1 1
+```
+
+#### Playing a sound file
+```bash
+aplay file.wav
+mplayer file.mp3
+```
+
+### Emergency Light
+#### Control Script
+```bash
+cat /usr/local/bin/emergency-light 
+#!/bin/bash
+
+PIN_ELIGHT=7
+
+# init
+gpio mode $PIN_ELIGHT output
+
+# command
+if [[ "$1" == "on" ]]; then
+	gpio write $PIN_ELIGHT 1
+elif [[ "$1" == "off" ]]; then
+	gpio write $PIN_ELIGHT 0
+elif [[ "$1" == "read" ]]; then
+	gpio read $PIN_ELIGHT
+else
+	gpio toggle $PIN_ELIGHT
+fi
+```
+
+### System Activity Light
+#### System Usage
+```bash
+uptime | head -n 1 | cut -f3 -d, | cut -f2 -d:
+```
+
+#### Daemon
+```bash
+cat /etc/systemd/system/system-activity-light.service
+[Unit]
+Description=System Activity Light Daemon
+
+[Service]
+ExecStart=/usr/sbin/system-activity-light-daemon
+
+[Install]
+WantedBy=multi-user.target
+```
+
+```bash
+cat /usr/sbin/system-activity-light-daemon 
+#!/bin/bash
+
+DELAY=10000
+
+while [[ true ]]; do
+	ACTIVITY=2000
+	TOP=`system-usage`
+	if (( $(echo "$TOP > 1.0" | bc -l) )); then
+		ACTIVITY=50
+	elif (( $(echo "$TOP > 0.75" | bc -l) )); then
+		ACTIVITY=100
+	elif (( $(echo "$TOP > 0.5" | bc -l) )); then
+		ACTIVITY=500
+	elif (( $(echo "$TOP > 0.2" | bc -l) )); then
+		ACTIVITY=1000
+	fi
+	echo $TOP
+	system-activity-light blink $ACTIVITY $DELAY
+done
+```
+
+```bash
+sudo systemctl enable --now system-activity-light.service
+```
+