Historical Radio, Mk. III

On display at the ITP winter show was the Mk. III version of the Historical Radio.

Overview

A conventional radio lets you travel through space: you can listen to stations from the local area, or with a shortwave or longwave radio, from broadcasters far away.  But the thing about a radio is that it’s stuck in the permanent present.  You hear what’s being broadcast in real time.  The Historical radio adds the dimension of time, providing for the ability to hear the past.

The time dimension is controlled by the tuning knob, moving longitudinally along the ‘tracks’ on the tuning dial.  The spatial dimension is radial, controlled by the band selector.  Each track represents a location/genre combination.  Ideally I wouldn’t have to combine those, see Mk. IV thoughts below.

The Time/Space switch, and associated indicator lights are for preprogrammed sequences, which march you along fixed in the dimension you select, either playing files related by being in the same time or same space.

The goal was to make something educational, more than just a “gee, isn’t it slick” project.  And the comments people had at the show were pretty much in line with what I was going for: “this belongs in a history museum!”

Behind the curtain

-it’s not a real radio.  [gasp]
inside is an Arduino Mega microcontroller, a Sparkfun / Robertsonics MP3 Trigger, an H-Bridge and a servo, and of course some LEDs.  Surprisingly it’s not as complicated as one might be led to believe.

The Arduino Mega was selected because I needed more digital I/O lines than the Duemilanove has available.  (Arduino development boards listing)

The H-Bridge was used to control the galvanometer.  See this post for a thorough discussion of how the H-Bridge works, including circuit diagram.

The MP3 Trigger was an adventure unto itself, see this post for a discussion of how to make that work.  I would recommend considering an Adafruit Waveshield or  other MP3 player.  I’ve heard good things about the Daisy: http://teuthis.com/daisy/index.html but haven’t seen it.  The main problem with the MP3 trigger is that the play and stop commands are both ‘O’ which requires some clever programming to get around.  See MP3 Trigger documentation for details.

Changes from Mk. II (previously named the Time-Travel Radio)

  1. More files, better alignment of events in Europe/America, and some RoW (rest of World) files, like Hirohito’s capitulation at the end of WWII, and some Che Guevara.
  2. debugged!
    – I found that I was not flushing the serial buffer as necessary, so it would occasionally lock up, waiting endlessly for the track-end signal.  Discussion of the necessary code for the MP3 trigger here
    I narrowed the ‘windows’ for the Q-Meter (the galvanometer tuning indicator) and the corresponding play window, to make more space.  if the switching is too fast (i.e. turning the tuning dial too fast/having the tuning windows too close together) makes it crash.  So that’s fixed.
  3. headphone jack (1/8” mini stereo) on front bezel
  4. hardware volume control – thanks to Eric Rosenthal for the circuit diagram.  Note: use a logarithmic potentiometer here, or you’ll get an exponential profile for the volume control (sound energy is logarithmic)
  5. ‘on station’ indicator on front panel, replacing power light.  This made it much easier for people to get the hang of using the radio, as few young people have used or seen a Q-meter.  One older man was ecstatic to see the Q-meter.  Hooray!

DSC_0510

 

Mk. IV

Nothing like this is ever done.  Things to do for Mk. IV

  1. 3D interface.  I would like to separate genre from geography, and perhaps do really zero in on the geographical dimension
  2. Maybe a full track of BBC, full track of CBC, Radio Moscow, etc.
  3. don’t wire together the Band selection LEDs, which makes for tough replacement when something burns out.
    DSC_0501
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