Intercom (Atmel ATtiny2313 microcontroller)
The movie "Ferris
Bueller's Day Off" is
a high school
comedy from 1986. It was a rather popular movie at the time
and for years afterward. Anyway, in the movie, there was a
scene where Ferris's high school principle
(Mr. Rooney) comes to Ferris's home and pushes the intercom button.
Ferris should be at home sick, but of course he is out for a
day, living it up. So, Ferris ingeniously hooked up an audio
player to give automated responses to anyone who presses the intercom
button. It doesn't take Mr. Rooney too long to figure out
that he is talking to a recording. Even though it didn't work
planned in the movie, it seems like an interesting idea to try on an
unsuspecting individual. <evil grin>
Figure 1: The
front panel of the Ferris Intercom
The user interaction could go something like this:
(Mr. Rooney walks up to the
front door and presses the round, faded intercom button)
(The Ferris Intercom outputs a hardy
(two second pause)
Ferris Intercom: "Who is it?"
(Mr. Rooney presses the intercom button)
Mr. Rooney: "It's Mr. Rooney"
(Mr. Rooney releases the intercom button)
(two second pause)
Ferris Intercom: "Oh, I'm
sorry, I can't come
to the door right now, I'm afaid in my weakened condition I could take
the stairs and subject
myself to further school absences."
(Mr Rooney leaves!)
In the movie, the intercom panel is brown and plastic looking.
Finding an exact replica of this
particular model proved difficult. So, a set of two
NuTone door intercom panels was ordered from E-bay. I thought
most likely way to make the intercom believable is to use a weathered
door intercom, to make it look like it has been there for a while.
Figure 2: A photo of the backside of the Ferris Intercom
The circuitry hardware:
The hardware is centered around a "Vinculum
VMusic2 MP3 player"
(that's a mouthful). The Vmusic2 is the gray box in Figure 3,
has the rainbow wires. The Vmusic2 is from a company called
makes playing an MP3 file from a thumb drive as easy as sending over
the correct serial string from the microcontroller. The thumb
drive is the silver cylinder in Figure 2, it is the back part of a
writing pen. One really nice thing about the MP3 player is
ability to jump from one sound file to another. If the
were to use an audio tape player, it would be rather difficult to keep
track of where the sound bytes are located on the tape. (And
also have to allow time to fast forward and rewind)
microcontroller is an ATTiny2313 from Atmel running at 4MHz.
ATTiny2313 has 2 Kilobytes of flash and 128 bytes of internal RAM.
This is more than enough to read button presses, light the
"talk" indicator, and send out a few bytes to the MP3 player.
Just about any microcontroller could have been used; even a
stamp could handle the hardware requirements.
Another part of the circuit consists of an audio amplifier to power the
speaker. The audio amplifier is an SSM2211, 1.5 Watt, IC in
pin SOIC package. There are several supporting components
amplifier IC. The circuit was pretty much unmodified from the
example configuration in the audio amplifier datasheet.
Figure 3: The insides of the Ferris Intercom
The MP3 player, thumb drive, and other circuitry draws about
at 5V. A wall transformer that outputs a regulated 5V into a
USB connector was used to power the circuit. This wall
transformer was originally used for a cell phone.
There isn't much to the software. Just sending out serial
strings, looking for button presses, and lighting the "push to talk "
LED at the correct time. One special item that was added
was resetting the audio messages back to the beginning if there has not
been any button presses for about 2 minutes. The code uses
1200 bytes of the 2K available flash in the microcontroller.
The MP3 files near the bottom of the page go into the flash drive
attached to the VMusic2 MP3 player.
Ferris Intercom "C" Source Code (WinAVR) (zipped)
Ferris Intercom Schematic
always, use at
your own risk!
*All rights reserved, all wrongs deserved*
Last Modified: January
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