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Raspberry Pi 2 as Intercom
Posted: Sat Feb 21, 2015 7:25 am
by mikaelarhelger
We are in the process of developing a carpark controller which are located next to the actual barrier. We wish to include an Intercom which allows communication to the management office. To add a microphone seems next to impossible unless one uses a USB Audio Adapter like this one:
- USB Audio Adapter
- 1475-00.jpg (25.35 KiB) Viewed 2444 times
As for the speaker (Visaton K 40 - 8 Ohm)
- Visaton K 40 - 8 Ohm
- k40_8_1.jpg (9.91 KiB) Viewed 2444 times
would it be best to connect it also to the USB Audio Adapter or directly to the Pi 2? If connecting a speaker directly to the Raspberry Pi 2 what should be the optimal impedance? The sound (speech only) should be heard 1-2 meter away (typical distance from driver of vehicle to intercom).
Re: Raspberry Pi 2 as Intercom
Posted: Sat Feb 21, 2015 8:29 am
by jimallyn
The RPi has a rather high output impedance, 50 ohms, so it isn't really intended to drive speakers. It might drive high impedance headphones OK. You're going to have to use an amplifier to drive your speakers.
Re: Raspberry Pi 2 as Intercom
Posted: Sat Feb 21, 2015 8:54 am
by mikaelarhelger
Thank you for your reply.
- 1. How about connecting a speaker to the USB Audio Adapter then?
2. What about connecting a 50 Ohm speaker like:
http://www.visaton.com/en/industrie/klein/k40_50.html
to the Pi?
Re: Raspberry Pi 2 as Intercom
Posted: Sat Feb 21, 2015 9:10 am
by ame
You need an amplifier.
You could use a speaker with a built-in amplifier.
More importantly, you need to try a few things and make some mistakes. There is no way you will come up with a fully-formed working design by asking questions on the internet. It's a good approach, but there's no substitute for trying some ideas and discarding the ones that don't work.
Re: Raspberry Pi 2 as Intercom
Posted: Sat Feb 21, 2015 9:16 am
by mikaelarhelger
Got it. Seems this is an idea solution then:
- 2.5W Class D amplifier
- 1712-00.jpg (47.34 KiB) Viewed 2372 times
Source:
http://www.adafruit.com/product/1712
Re: Raspberry Pi 2 as Intercom
Posted: Sat Feb 21, 2015 9:21 am
by ame
Good find. But, if you are in Hong Kong maybe there's a technology market you can go to to buy stuff like that (and you won't have to wait for delivery). A lot of the stuff I buy from DealExtreme is shipped from Hong Kong. Who knows what other cool goodies you can find for your project!
Re: Raspberry Pi 2 as Intercom
Posted: Sat Feb 21, 2015 10:52 am
by Bruny
this would be interesting:
IP Video Door Station on Raspberry Pi with PoE 802.3af 
Re: Raspberry Pi 2 as Intercom
Posted: Sat Feb 21, 2015 11:59 am
by PiGraham
If you want the intercom to be audible over street noise at >2m I'd guess you want >=5W RMS amp. (only a guess)
Try it out in your environments.
If you think ~2W is loud enough the Cirus/Wolfson audio card might be a good fit. On-board microphones and 2W class-D amp.
http://www.element14.com/community/docs ... and-b-plus