Alternate ways to generate tone

Posted: 5/8/2013 2:21:26 PM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

Hi thewriter

"I've circled, in the picture below, what I think is what you meant by "circuitry up to varbuf and refbuf". Again, I've probably circled the wrong parts."

Include C35 in your circle, and you got it spot on.. As for the "I've never dealt with layouts this complex...and that's a bit sad since I imagine this is one of the more lesser complex schematics. " The full H1 is much more "complex" than many theremins "out there" so dont worry about this..

"Unfortunately, I don't have access to a scope nor do I own one."

You need to get one! - Without a 'scope you are blind - IMO, there are a few essential tools if you are doing anything other than building a simple theremin kit - You need a 'scope, good multi-meter, and a frequency counter... Then if designing analogue stuff, you need a good simulator like LT-Spice.

Particularly if you are not competent with analogue, LT-Spice is essential - it allows you to investigate current flows and voltages which are impossible to measure on a real circuit, and helps one gain understanding of circuit operation. The 'scope can be almost anything - a 2nd hand 20MHz analogue 'scope can be picked up on ebay for probably about $30, or you can get a Nano digital 'scope for about $60. Although not absolutely essential, a frequency counter like the YAEGE FC1 with a BNC adaptor is cheap and makes life a LOT easier.

Unlike digital, where one is dealing with binary and numeric sequential operations mainly, Analogue is far more "hands on" IMO.. You spend a lot of time with an active board, LOOKING at signals and working out what you have done "wrong" and changing components to get things "right".. You need to see the circuit operation (with a 'scope) to do this.


ps - I have pasted your circled schematic ... At the bottom right corner the comparator circuits are shown - the output from these comparators are the reference and variable oscillator signals converted to logic level square waves.. these can be taken directly to your digital stuff.... The whole circuit board layout is given in the article, so one could just take the front-end and comparators and lay these out based on this.. You then have a simple proven front-end.

The output of the comparators could also be taken to a D-Latch as shown in the next page of the schematic.. The otput of this gives a square wave at the difference frequency. The H1 did analogue (the analogue multiplier) Mixed signal, and even some "real" digital processing (The PSoC compared the reference and variable oscillators to give a null output).. Get rid of everything except the oscillators and comparators, and the signals into the PSoC are the digital signals you need.

I think the above is the simplest - But probably not the best!

(I ALSO NEED TO MAKE IT CLEAR THAT THE CIRCLED SECTION IS A COPY, ALMOST IDENTICAL TO THE EPE-2008 THEREMIN's FRONT-END.. IT IS NOT MY ORIGINAL DESIGN! - In particular, there is no linearization, and linearization cannot be easily incorporated.. You would need to linearize in the digital domain.. "out of the box" the linearity is usable but not good)

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