[sdiy] Re: diodes/LDR

[fmg]

Harry, and the list

Now that you mentioned the PV-1 I want to share some questions about diferents
methods of F/V convertion. I searched the web for info and get some text about,
(found less than I expected to find) explaining diferents methods that seem to
me are variants (simple or very complex sometimes) of a only one that have a
charging/discharging capacitor as core.
This implies that the designer have to decide what he wish to get, a fast system
with an imprecise response or a precise one but too slow to follow small or 
large fast changes.

(please note that I arrive to this technic as a complete ignorant and my
opinions/deductions could be wrong) 

I also found documentation about mixed analog/digital methods to obtain
a voltage (or current) with direct dependence of a given frequency, wich could
be constant or variable, but these implementations have one of their stages based
in the temporal storage of a charge in a capacitor (or several capacitors) for
the conversion process and suffer of the same binary issue giving you again the
election: ripple or a slow response

I have no found concrete information about pure digital methods of f/v conversion
and this makes me wonder if there is a sort of "trade secret" about such methods
or I searched in wrong places.

Going off topic I remember when was in school (many years ago) our e-teacher
left to us to decide what project we wished to develop to school science exhibition.
I proposed the design and construction of a digital frequency counter based in
the CMOS 4000 series (slow but cheap). My classmates complain alleging complexity
and/or dificulties but then I assured that the word "digital" and a lot of
changing numbers in a led display should be enough to ruin them the party to the
other grades projects. I won ...and got the attention of some girls (ok, it was
a tech-school, they were tech-girls, and I was so young... )

The next year we were running out of money then for the next science exhibition
I suggested that we could modify the last year frequency counter and add it a
period measuring option. It could be simple to implement, just putting the clock
frequency in the signal-in and using the "unknown" signal as sampling rate. (We have
used 1 or 2 Mhz clock divided to get a 0.5s sampling rate, I remember clearly,
specially the chain of 4017s).  With this method we only must be sure that the
"unknown" signal should be lower than the clock, and all our investment could be
reduced to the cost of a switch. (I lost ...we presented a thyristor lamp dimmer)

Going on topic again I wonder if exist a f/v (or pitch to cv) converter based in
this principle, (measuring the period of a wave by digital methods and then
converting the info to an analog signal)
Is there a company producing such converter ? ..is this method patented or under
trade secret ? ...or was abandoned for something I miss ?

I think such method should not be hard to implement for musical purpose, it
could have good accuracy ...and could be fast.

Whats your opinion ?
(I have the PV-1 schem in hands and know your pitch > cv experience is far away
from mine)

Any response welcome, respectfully,

Fabio Gonzalez
Posadas, Argentina

harrybissell wrote:
> 
> Hi Dan...
> 
> I wasn't really attempting to be 'snippy'... just playful.
> I might even reverse engineer one just for the fun of it.
> 
> The points were (as I saw them) that the MoogerFooger is
> a current product for Big Briar and if they wanted to
> post schematics it would be their business.
> 
> Most of the effect schematics on the web have been there for
> many years, are often the result OF reverse-engineering and are
> not scans of manufacturer's documents (unless they are long
> out-of-business).  Even then, a scan of a schematic used without
> permission violates copyright laws.
> 
> The comment (not mine) to "Ask Bob" was not flippant at all. Bob
> Moog HAS been known to offer information when asked.  He gave me
> permission to make the PV-1 pitch to voltage converter based on his
> design.  All he asked was that the board have the text "Based on Etherwave
> Pitch to Voltage converter by Bob Moog, used with permission" and that I
> send him a unit to play with. So I did.
> 
> I think that Bob recognised that the product would not be commercially viable...
> 
> based on his knowledge of the Theremin market. He was actually doing everyone a
> favor by giving permission... maybe some folks might even buy a theremin to go
> with the converter...
> 
> The MoogerFoogers are a different story... posting schematics would probably
> not enhance the sale of $300 units (expensive for you and me both....).  But I
> think
> the advice given (in a light-hearted way) is really valid.  Reverse Engineering
> is a
> protected practice (its NOT illegal)... and the community would benefit from the
> 
> information.
> 
> Its also possible that the information is "Trade Secret" (as opposed to
> patented)
> in which case there is no way that you will be given a schematic by Big Briar...
> 
> as trade secret protection implies that the only way you could have gotten the
> information is by theft.
> 
> Again, sorry if I came off as snippy. Not my intention at all....
> 
> H^) harry
>