[sdiy] Real slow LFO ICs?

[Theo]

Why not use a "standard" Opamp based tri/saw/square LFO?
JFET Opamp like TL072 can go quite slow.
When one opamp is used for a 1/2V+ reference a 074 can be a nice slow single
supply LFO.

Cook book receipt:
Start with a standard triangle LFO.
Take 100k & 47k for the feedback resistors around the comparator.
Use a 10k potmeter for the rate potmeter and use it in divider mode (like
usual),
the top of the pot connects directly to the comparator output.
Now add a 4M7 series resistor on the wiper towards the timing cap.

In this setup even a small 470nF timing cap gives a "fastest" rate of
0.053hz!!!
The slowest rate would be roughly 200 times slower,
around 0.00026 hz or round about 1 hour period.
This depends on the supply voltage and quality of the pot meter tough.
A good pot and enough supply voltage can give you more than double the 200
times range.

A smaller wiper resistor and or a smaller timing cap raises the max
frequency.
Best to start with a smaller resistor and when down to 1M or so a smaller
cap.

Formulas:
For the fastest rate: frequency = (1/(4RC))(R2/R1)
Where:
- R and C are the timing cap and the wiper series resistor.
- R1 and R2 are the feedback resistors around the comparator.

For the slowest rate: roughly 200 times the fastest rate.

A diode from the timing cap to the top of the rate potmeter changes to SAW
operation.
However the rate doubles.

Note: works best with +/-12V or more supply voltage.
With a +5V single supply the range selectable by the pot could become
smaller than the factor 200 stated above.

Have fun.
Theo



----- Original Message -----
From: Troy Sheets <tsheets at atari.saturn5.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Monday, October 27, 2003 10:01 PM
Subject: [sdiy] Real slow LFO ICs?


>
>
> Hi, I am looking for a super-simple LFO IC... or multiple LFOs in a single
> package.  sine or saw output will be fine, must be able to run in the
> sub-1hz range.
>
> Anyone have any tips?  This is for an EL-wire project, not for audio...
> so 0-5V range is OK.
>
> -troy
>
> --
> --------------------------------------------------------------------------
----
> tsheets at saturn5.com                                  <- You have found me
> http://www.saturn5.com/tsheets/audio                 <- my .mp3 tracks
> "I just don't have the discipline to be a hippie"    <- Homer J. Simpson