mikaelarhelger
Posts: 3
Joined: Sat Feb 21, 2015 6:59 am
Location: Hong Kong

Raspberry Pi 2 as Intercom

Sat Feb 21, 2015 7:25 am

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:
1475-00.jpg
USB Audio Adapter
1475-00.jpg (25.35 KiB) Viewed 2195 times
As for the speaker (Visaton K 40 - 8 Ohm)
k40_8_1.jpg
Visaton K 40 - 8 Ohm
k40_8_1.jpg (9.91 KiB) Viewed 2195 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).

jimallyn
Posts: 51
Joined: Wed Nov 12, 2014 9:13 am

Re: Raspberry Pi 2 as Intercom

Sat Feb 21, 2015 8:29 am

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.
“So you say you love the poor? Name them.” - Gustavo Gutierrez

mikaelarhelger
Posts: 3
Joined: Sat Feb 21, 2015 6:59 am
Location: Hong Kong

Re: Raspberry Pi 2 as Intercom

Sat Feb 21, 2015 8:54 am

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?

ame
Posts: 3172
Joined: Sat Aug 18, 2012 1:21 am
Location: Korea

Re: Raspberry Pi 2 as Intercom

Sat Feb 21, 2015 9:10 am

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.

mikaelarhelger
Posts: 3
Joined: Sat Feb 21, 2015 6:59 am
Location: Hong Kong

Re: Raspberry Pi 2 as Intercom

Sat Feb 21, 2015 9:16 am

Got it. Seems this is an idea solution then:
1712-00.jpg
2.5W Class D amplifier
1712-00.jpg (47.34 KiB) Viewed 2123 times
Source: http://www.adafruit.com/product/1712

ame
Posts: 3172
Joined: Sat Aug 18, 2012 1:21 am
Location: Korea

Re: Raspberry Pi 2 as Intercom

Sat Feb 21, 2015 9:21 am

mikaelarhelger wrote:Got it. Seems this is an idea solution then:
1712-00.jpg
Source: http://www.adafruit.com/product/1712
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!

Bruny
Posts: 159
Joined: Fri Feb 06, 2015 5:22 pm

Re: Raspberry Pi 2 as Intercom

Sat Feb 21, 2015 10:52 am

this would be interesting:
IP Video Door Station on Raspberry Pi with PoE 802.3af 8-)

PiGraham
Posts: 3571
Joined: Fri Jun 07, 2013 12:37 pm
Location: Waterlooville

Re: Raspberry Pi 2 as Intercom

Sat Feb 21, 2015 11:59 am

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

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