Ethereum Ticker on Wemos D1 Mini with OLED Shield

wemos-d1-oled-eth-ticker

btc = 0
usd = 0
json = {}
doGetData = true
currencyLabel = "BTC"
currencyValue = btc

-- setup I2c and connect display
function init_i2c_display()
    -- SDA and SCL can be assigned freely to available GPIOs
    local sda = 2 -- GPIO14
    local scl = 1 -- GPIO12
    local sla = 0x3c -- 0x3c or 0x3d
    i2c.setup(0, sda, scl, i2c.SLOW)
    disp = u8g.ssd1306_64x48_i2c(sla)

    prepare()
end


-- graphic test components
function prepare()
    disp:setFont(u8g.font_6x10)
    disp:setFontRefHeightExtendedText()
    disp:setDefaultForegroundColor()
    disp:setFontPosTop()
    disp:setScale2x2()
end

function draw()
     disp:drawStr(0, 0, currencyLabel)
     disp:drawStr(0, 12, currencyValue)
end 

function updateDisplay()
  -- Draws one page and schedules the next page, if there is one
  local function drawPages()
    draw()
    if (disp:nextPage() == true) then
      node.task.post(drawPages)
    end
  end
  -- Restart the draw loop and start drawing pages
  disp:firstPage()
  node.task.post(drawPages)
end

function getData(callback) 
    json = {}
    http.get("http://ethereumwisdom.com/data/ethereumwisdom.json?" .. tostring(math.random(), nil, function(code, data)
        if (code < 0) then
            print("HTTP request failed")
        else                
            json = cjson.decode(data);

            btc = string.sub(tostring(json.currencies.BTC.markets.poloniex.price),2,6)
            usd = string.sub(tostring(json.currencies.USD.markets.poloniex.price),1,5)

            callback()
        end
    end)

end

function showNextCurrency()
    if ( currencyLabel == "BTC" ) then
        currencyLabel = "USD"
        currencyValue = usd 
    else
        currencyLabel = "BTC"
        currencyValue = btc
    end

    updateDisplay()
end

function runloop() 

    if ( doGetData ) then
        getData(showNextCurrency)
        doGetData = false
    else 
        showNextCurrency()
        doGetData = true
    end

end

function init() 
    init_i2c_display()

    tmr.alarm(1,5000,tmr.ALARM_AUTO,runloop)
end

init()