Raspberry Pi 2 as Intercom

[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 2445 times

As for the speaker (Visaton K 40 - 8 Ohm)

Visaton K 40 - 8 Ohm

k40_8_1.jpg (9.91 KiB) Viewed 2445 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]

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.

[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?

[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.

[mikaelarhelger]

Got it. Seems this is an idea solution then:

2.5W Class D amplifier

1712-00.jpg (47.34 KiB) Viewed 2373 times

Source: http://www.adafruit.com/product/1712

[ame]

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]

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

[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