Background
We live 4 miles from a nuclear power plant, and we also have a GMRS repeater station that we use for Community Watch in our neighborhood. We also live in an area that tends to have severe thunderstorms and sometimes tornado warnings. I was looking for a way to pipe automated emergency warnings (nuclear, weather, and other emergency) into the community watch repeater and have them automatically broadcast to families in our community that have GMRS radios on the system. This would allow community watch handset radios to also be used to receive these emergency broadcasts via the repeater when they are broadcast via NOAA. The review of the Sangean CL-100 Weather Alert/Public Alert receiver is documented here based upon this use case.
The CL-100 has both audio outputs and an alert trigger output that is useful for triggering external devices (strobes, bells, sirens, etc). Since my Harris HDR-100 repeater has external PTT (push to talk) triggering to allow an external device to key the transmitter, I was able to use a small arduino micro to pickup the trigger output from the CL-100, and drive a TTL operated relay to engage the PTT line on the repeater. I set the arduino to receive the CL-100 trigger on pin 5 (which is tied HIGH) as an INPUT. When the CL-100 triggers pin 5, it causes the arduino to set pin 7 HIGH for 2 minutes upon pin 5 going LOW when triggered. 2 minutes should be enough time for any emergency alert to be rebroadcast over the community watch repeater station. After the 2 minutes expires, the PTT line is released by the relay.
The code for the arduino to key down the relay for 2 minutes is here:
void setup() {
//configure pin 5 as an input and enable the internal pull-up resistor
pinMode(5, INPUT_PULLUP);
pinMode(7, OUTPUT);
}
void loop() {
//read the pushbutton value into a variable
int sensorVal = digitalRead(5);
if (sensorVal == HIGH) {
digitalWrite(7, LOW);
} else {
digitalWrite(7, HIGH);
// set 2 minutes (in milliseconds) to hold PTT engaged
delay(120000);
}
}
The signal trigger from the relay unit is connected to pin 7 on the arduino. Both the relay module and the arduino are powered by a 5V DC supply. The N.O. (normally open) contacts on the relay are connected to the Harris HDR100 repeater external PTT input. The CL-100 alert output is connected to pin 5 and GND on the arduino. The rear of the CL-100 has the various signal outputs that are useful in this application. Audio output from the CL-100 is directly fed to the repeater flat TX audio input on the HDR-100 repeater and volume is set for reasonable level on rebroadcast audio at the CL-100. When the PTT is engaged for 2 minutes by the CL-100, this causes alert program audio to be immediately rebroadcast over the community watch repeater.
This setup makes an inexpensive automated emergency alert system that benefits us and our neighbors who participate in the community watch system in our community. The repeater station and alert receiver will also continue working during extended power outages with available on-site generator power.
