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summer news

Hmm whats up lately… I signed up as a Wikipedia editor and contributed several paragraphs to the article on perfboard.

You can now find Bodytronix tracks on my SoundCloud .  We’re playing Friday July 2nd at the ND @ 501 Studios.  Come have fun with us, Pong, and Woodgrain.

Handmade Music Austin #9 (nine already!?) is coming up on Sunday afternoon July 11th at the usual location, Salvage Vanguard Theatre in Austin TX.  I came up with a new basic level project called 1976 Phototheremin.  Here’s a demo:

The original circuit is by Forrest Mims III, from the book OPTOELECTRONIC PROJECTS vol 1.  I fell in love with this circuit when I saw it, because it is ultra-minimal.  It has only seven components including the battery and speaker.  Its real transistor magic.  The active circuit is just two transistors, a capacitor, and photocell.  I’ve crossed my fingers that the PCBs will get here in time for the workshop.

I’ve also been experimenting with voltage-controlled oscillators.  In particular the 4069 CMOS VCO of René Schmitz.  I got rid of the PWM section and built two VCOs from one CD4069.  The temperature compensation method deserves some re-working however, because Schmitz’s design requires one tempco resistor per CV input.  It would more efficient to use one tempco per VCO.  So I am consulting some of the other VCO designs I see, including a nice one by Ian Fritz that you can see here.

In order to appreciate the subtleties of temperature compensation, the VCO must be tuned accurately.  This can be a chore so I imagined a circuit to make it easier.  It is just a voltage sequencer that outputs stairstep waveforms with 1.00V intervals.  This makes the VCO play descending octave intervals, and its easiest to hear if it is tuned accurately.  Here’s more information, and a demo.