BRKR = "aaa.bbb.ccc.zzz"    -- IP/hostname of MQTT broker (Raspberry Pi)
PORT = 1883                 -- MQTT broker port
USER = "youruser"           -- If MQTT authenitcation is used then define the user
PSWD = "yourpswd"           -- The above user password
CLID = "2_LED"              -- The MQTT ID. Change to something you like

TPIC = "fire"               -- MQTT topic to subscribe

gpio.mode(3, gpio.OUTPUT)   -- GPIO0 shutter open
gpio.mode(4, gpio.OUTPUT)   -- GPIO2 flash fire
gpio.write(3, gpio.HIGH)
gpio.write(4, gpio.HIGH)

tmr.alarm(0, 5000, 1, con_broker) -- mS time

function con_broker() -- connect to the MQTT broker
    print('WAIT:','MQTT BRKR')
    m = mqtt.Client(CLID, 0, USER, PSWD)
        m:connect(BRKR , PORT, 0, function(conn)
            print('BRKR:',BRKR)
            print('PORT:',PORT)
            print('CLID:',CLID)
        sub_mqtt()      --run the subscription function
    end)
end

function sub_mqtt()
    m:subscribe(TPIC , 0, function(conn)
        print('TPIC:',TPIC)
    end)
    tmr.stop(0)
    main()
end

function main() -- main program
    print('MAIN:','PROG')
    m:on("message", function(conn, TPIC, data) -- Callback to receive the subscribed topic messages
        if data == "4_LED" then -- 4_LED client (other camera|flash relase)
            data = nil
        elseif data == "2_LED" then -- this client
            data = nil
        end
        if (data ~= nil) then
            print('TPIC:',TPIC,data)
                if (data ~= CLID) then
                    m:publish(TPIC,CLID,0,0, function(conn) end)
                    if data=="flash" then
                        gpio.write(3, gpio.LOW)  -- shutter open
                        tmr.delay(126000)        -- min/max uS delay for 1/250s
                        gpio.write(4, gpio.LOW)  -- flash fire start
                        tmr.delay(25000)
                        gpio.write(3, gpio.HIGH) -- shutter close
                        gpio.write(4, gpio.HIGH) -- flash fire stop
                    end
                end
        end
    end)
end