PMR remote horn

As LSC current has quite a small fleet of racers, there are times when we run races from one of the boats racing...

To allow a shore based 'car horn' to be remotely sounded from a boat on the water. I have modified an old PMR radio to include a opto-Isolator which, when receiving, energises the input side of a large current Solid State Relay (SSR), with the output side supplying the horn (for testing, a cheap 12v car horn).

So another PMR on the same frequency/channel, transmits, it will make the the modified one switch to receive, and therefore sound the horn.

I tested this today (11-Aug-2019), and it seems to work ok, but need to test on the water to check the 'coverage' :o)

My aim is to also add a WiFi relay module in parallel with the opto-isolator output (see diagram), so that the DRSC app can also trigger the horn.

If this all works, I may replace the relay module with just a ESP8266 to driver the SSR input directly, which should make it react quicker (i.e. SSR faster to switch than mechanical relay). This may well be added to the current prototype circuit I've created to drive the LED time display (see above).