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using my doorbell to trigger music that wakes me up

Wed Dec 14, 2016 9:17 pm

Hello everyone,

I want to connect my wireless door bell to a raspberry pi to play music when the bell activates.
sounds easy but it isn´t. I already asked the manufacturer if there is a place on the PCB where i could connect to.
they told me: the version you plug into a outlet is always under current. the led only indicates power and the speaker also is not at 0V while off.

so i was thinking i could wire the speaker and the 3.3v output with a NAND-gate to an input pin.
as soon as the speaker plays music he should get 0V as part of his audio signal. i know a simple transistor would do the trick but with a NAND gate i can monitor something else with the same circuit. i know my diagram is missing some resistors and a ground connection, but those are not the problem. i think a NAND microchip wont be able to handle the speaker signal but i have no clue what kind of transistor to use to build my own NAND gate.

all help is appreciated. especially if you can tell me a faster way to find the right transistor model than checking datasheets until i find the right one by chance. if my plan is stupid, just tell me why please. i know i only know the basic concepts of electronics so you wont make me cry;)

Thank you for your time,
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Re: using my doorbell to trigger music that wakes me up

Thu Dec 15, 2016 6:18 pm

I wonder if you're approaching this the wrong way?

You want to detect the audio signal, which appears to sit on some DC level; so why not remove the DC by putting it through a capacitor.
Then, you could either have the "silence" at 3v3 and have it go to 0v for "sound", or the other way round.
Whichever, a simple rectifying circuit should suffice.
Following that, a capacitor to prevent multiple triggering, a resistor to discharge the capacitor, and a zener to prevent the signal from going outside the range of the GPIO.
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Re: using my doorbell to trigger music that wakes me up

Fri Dec 16, 2016 10:04 am

Another completely different approach is to take advantage that it is a wireless doorbell. The bell push will be transmitting a code probably at 433MHz (should be documented somewhere on the unit.

You can get very cheap 433MHz receiver modules which can attach to the raspberry. Then it needs a bit of research to work out the coding used. There are quite a lot of examples around on the net.

Big plus is that you don't have to physically change anything on the doorbell unit itself.

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Re: using my doorbell to trigger music that wakes me up

Fri Dec 16, 2016 9:59 pm

How is this doorbell receiver powered?

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