Detect sound


Hi all,
A friend of mine who lives in an apartment complex reprogrammed the door phone so that it automatically open the front door down stairs when someone rings his doorbell. I think this is a brilliant Idea, however my door phone can’t be reprogrammed. So currently I am controlling it through openhab/Amazon Echo (soldered out the open button to relay hooked up to rpi with OH). But it would be nice to just press my name and then the door opens(like when coming home with ur hands full, and not to thumble around with keys).

So how can I achieve this? My idea is to hook into the speaker on the door phone and when this reach a certain level then door opens. RPI does not have analog input and also a speaker is AC signal, which means it needs to be converted to DC signal. Is there a simple IC/breakout board I can use to convert the audio signal to digital 0 and 3.3V signal? Or could i somehow use the HDMI or get an USB mic?

Any idea would be nice

I’d think a small USB mic would be the way to go. Google for “raspberry pi sound detection” for lots of ideas.

Great, maybe get this one and solder the speakers cable directly instead of the mic?

I guess that means anyone can get into your building then by just pressing your name?

I kinda agree with TommySharp. It’s not really my business but it seems like you are compromising the security of the building for all tenants just for your own convenience. To some that door may be a nuisance, to others a peace of mind. If I lived in your building and found out, I wouldn’t be happy. I suspect if you ask your landlord if you could do this, they would say no. Probably a good indication.

Perhaps better would be a button on your app to push the button for you. That way it at least isn’t out in the open for all people to try.

Hehe, I was kinda of just waiting for someone to comment on that one, even surprised it took so long…

Well if you are a burgular it takes you about 30s to open the door anyway, either by just breaking the window and turn the inside lock or by just have proper tools. Or you can just ring any doorbell and people will open for you eventually(people are not really sceptical) or just wait to someone else is going in. And where does it get you? Into a hallway with 15 locked doors, which you then have to break into… And the most important factor is that this is Norway…

So I don’t really see the safety problem, and first of all they need to know about it… and press the correct doorbell…

No comment on your idea of safety… if it’s just to detect the level of sound, you can use one of these as do I. There’s an analog and a digital output, including a potentiometer to set the trigger level.

Great, do you think i can just desolder the mic and solder the an mono-jack on it instead and use it as line in instead of the mic?

I think I might even have one of those laying around anyway.

I think yes, but you will likely need a constant 3.3-5V supply (such as a CR123 or a couple of AA batteries).
I actually attached my doorbell pusher to a Fibaro binary sensor and removed the real doorbell. Now it’s playing a MP3 sound through my Pi instead. That way, you can at least implement some logics here (such as to disable the mechanism at specific times of day or when you’re at home).