OPTIONAL! This is possible to add  more camera | flash relase clients. In my case there is another one client with unique name (CLID = “4_LED”) and IP adress.

Firing MQTT clients from cameras hot shoe | PC connector is an different option (see Schematic 2) – it needs to comment or remove shutter open-close and flash timer delay in LUA client code.

 mqtt.lua – flash | shutter relase code 
if data=="flash" then
--                gpio.write(3, gpio.LOW) -- comment GPIO0 - shutter open
--                tmr.delay(126000)       -- comment min/max uS delay for 1/250s
gpio.write(4, gpio.LOW)                   -- flash fire start
--               gpio.write(3, gpio.HIGH) -- comment GPIO0 - shutter close
gpio.write(4, gpio.HIGH)                  -- flash fire stop


Of course no need to use GPIO0 as shutter pin, no need to N3 cable! Focus | shutter are set | operating in camera – MQTT clients are firing only the flash(es).