Вот вполне рабочий вариант (nodemcu-firmware/tcp2uart.lua at master · nodemcu/nodemcu-firmware · GitHub)
wifi.setmode(wifi.STATION)
wifi.sta.config("SSID", "PASSWORD")
uart.setup(0,9600,8,0,1,0)
sv=net.createServer(net.TCP, 60)
global_c = nil
sv:listen(9999, function(c)
if global_c~=nil then...