1.2" 7-segment LED display, nodeMCU ESP8266, MAX7219 HT16K33

displays = { main = 0x70 }

function init( addresses, sda, scl )
    i2c.setup( 0, sda, scl, i2c.SLOW )
    for name, address in pairs( addresses ) do
        write( address, 0x21 ) -- enable screen
        setBrightness( address, 1 ) -- min brightness
        output( address, "    " ) -- clear display
    end
end

function setBrightness( address, val ) -- 0 - off, 1 - 16 brightness level
    if val < 1 then
        write( address, 0x80 ) -- display "off"
    else
        if val > 16 then val = 16 end
        write( address, 0x81 ) -- display "on"
        write( address, 0xE0 + val - 1 ) -- brightness 0 - 15
    end
end

function setBlink( address, yes )
    local val = yes == true and 0x85 or 0x81
    write( address, val ) -- blink or display "on"
end

function output( address, txt ) -- pass exactly 4 char string
    if txt:len() ~= 4 then return nil end
    write( address, { 0, chr( txt:sub(1,1) ), 0, chr( txt:sub(2,2) ), 0, 0, 0, chr( txt:sub(3,3) ), 0, chr( txt:sub(4,4) ) } )
end

function chr( x )
    local c = {[" "]=0,["0"]=63,["1"]=6,["2"]=91,["3"]=79,["4"]=102,["5"]=109,["6"]=125,["7"]=7,["8"]=127,["9"]=111,b=124,o=92,t=120,n=84,c=88,Y=110,E=121,S=109,N=55,O=63,A=119,D=63,d=94,l=6,L=56,P=115,B=127,C=57,F=113,G=61,H=118,I=6,J=14,R=119,U=62,Z=91}
    if c[x] == nil then return c[" "] end
    return c[x]
end

function write( address, data )
    i2c.start( 0 ) -- it is always zero
    i2c.address( 0, address, i2c.TRANSMITTER )
    i2c.write( 0, data )
    i2c.stop( 0 )
end

init( displays, 1, 2 )
output( displays["main"], "BLAH" )