A doorbell is great for letting you know when someone is at the door.
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But what do you do, if your music is turned 100% up. Or you sit with headphones… You won't know someone rang your doorbell. And you'll have to wait another day for that package you have been waiting for so long on…

• A doorbell, that provides some voltage when button is pressed. My wired doorbell supplies 4V (hint: wireless doorbells might have an LED on them ;))
• Some resistors. I used 1k, 100, 47, 10
• ESP8266, I used a dev kit for this. In the future I will hide a ESP-12 or simular inside the doorbell.

If you have a wired doorbell, and it doesn't have a voltage out like mine on button press. Get a “Current Sensor Module” on ebay. This will then give you a voltage out! But beware that it also give you voltage while idling (so change the script to where the threshold fits). Just beware that current sensors isn't the most stable solution. As magnets tends to affect them ;)

If you have a wireless doorbell, poke around with a multimeter and see where there is power while button is pressed (LED, Speaker??). If you don't really know what you're doing, you should be ready to by a new unit or get a second receiver that you can play on.

Since I want an instant notification, I choose to power this instead of letting it be powered by the batteries (takes 2-3 seconds to connect to wifi).

The ADC port on the ESP8266 can maximum handle 0.978V, so you need a simple resistive voltage divider.

The voltage divider I decided to make, will turn 7.2V (“V_in”) down to 0.978V (“V_out”).

This gives me 0.550V_out when V_in is 4V.
<br>For resistance I used 1k as R₁ and 157 as R₂ (The 157 was made by connecting 100+47+10 in series). And the GND should be the same on all 3 things.

I was lazy, so I just used NodeMCU. I wanted to use MicroPython, but that seems to run the chips very hot. I prefer that you can't even feel they are on.

tmr.alarm(2,50, 1, function() 
    currentADC = adc.read(0)
    if currentADC > 20 then
        -- Button is currently pressed!
        print("C-ADC: "..currentADC.. " P-ADC: "..previousADC)
        if previousADC < 21 then
            previousADC = currentADC -- Fix for long HTTP requests...
            -- slicknet:send("STROBE 300,5000")
            -- slicknet:send("DOORBELL " .. node.chipid())
            conn=net.createConnection(net.TCP, false) 
            conn:on("receive", function(conn, pl) print(pl) end)
            conn:connect(8888,"ws.mathias.local")
            conn:send("GET /notify?type=button&id=doerklokken&value="..currentADC.."&nma HTTP/1.1\r\nHost: ws.mathias.local\r\nConnection: keep-alive\r\nAccept: */*\r\n\r\n")
        end
    end    
    previousADC = currentADC
end)
-- Don't forget to add a "keep alive" script too!! Sometimes ESP's wifi gets stuck pretty easily.

• Make this page look better, it's a terrible mess right now.
• Find a 3.3v voltage source, if not faster connection time can be achieved. And hide a small ESP inside the doorbell.
• Maybe find an I2C ADC module, so doorbells battery voltage also can be monitored?
• Switch to MicroPython for faster connection time, and power doorbell AND ESP at once? ..and hide it in the case