[sdiy] THAT 2155 on sale

Kylee Kennedy kmkennedy at gmail.com
Sat Apr 11 08:53:48 CEST 2020

I'm with Adam who said use your ears in the diode testing thread.
I have an LPG pcb with sockets for the vactrols and while using the same
trigger and noise source for all tests just go in and swap vactrols.
I go with the vactrols that sound the best. Some I like the ping/bongo
sound while others I like for their slower filter sweep long tail response.

So I usually end up with two LPG's per panel with different responses.

Trial and error,

PS I did go through a period where I would capture the tail response on my
Rigol scope single shot capture. Also use my Fluke multimeter to compare
their on resistance and off resistance. This did help me remove wildly low
resistance variable vactrols.

On Friday, April 10, 2020, Laughing Man <laughingman647 at gmail.com> wrote:

> I'll give the comparator circuit a shot, though I'm still curious what the
> datasheet is referring to in regards to some specific amount of current
> being pushed through the LDR. The Excelitas datasheet also mentions that
> currents lower than 1mA would result in excessively high resistances.
> That's the main thing that's stopping me from being sure I've tested them
> right: I'm not sure how I know I've got the right amount of current flowing
> through the LDR. If I don't, then the specs won't line up by a long shot.
> It seems as if I just have to get a 'golden vactrol' that I know will work
> in the situation I want, and just line them up, which is bugging my
> scientific side.
> On Fri, Apr 10, 2020 at 10:08 AM Ullrich Peter <Peter.Ullrich at kapsch.net>
> wrote:
>> Hi Pete!
>> To show curves from an Arduino you don't need a display, you can do it
>> with the serial interface via USB and the Arduino IDE itself by using the
>> serial plotter!
>> See here: https://www.instructables.com/id/Ultimate-Guide-to-Adruino-
>> Serial-Plotter/
>> Ciao
>> Peter
>> http://www.ullrich.at.tt
>> ________________________________________
>> Von: Synth-diy <synth-diy-bounces at synth-diy.org> im Auftrag von Pete
>> Hartman <pete.hartman at gmail.com>
>> Gesendet: Freitag, 10. April 2020 17:17
>> An: synth-diy at synth-diy.org DIY
>> Betreff: Re: [sdiy] THAT 2155 on sale
>> On Fri, Apr 10, 2020 at 8:43 AM Oren Leavitt <obl64 at ix.netcom.com<mailto:
>> obl64 at ix.netcom.com>> wrote:
>> I have an idea for "quick matching" photo cells.
>> Basically one op-amp - a comparator with hysteresis (like that of a basic
>> LFO)
>> 1) Put the photo cell side in a resistor divider and connect to the
>> comparator input.
>> 2) Connect comparator output to to LED side thru appropriate current
>> limit resistor.
>> The circuit should self oscillate at an amplitude/frequency determined by
>> the LDR's light/dark resistance and lag time characteristics. Plug
>> different photocells into same circuit and sort them by matches in
>> amplitude/frequency shown on oscilloscope.
>> An idea..
>> I rather like it.  I've occasionally started putting on paper ideas for
>> using an Arduino where an analog output drives the LED and steps from 0 to
>> 5V (with appropriate current limiting of course) and an analog input reads
>> from a voltage divider including the resistive side.  The idea being to get
>> a graph.  But then I got stuck on how to display the graph meaningfully
>> without going full blown OLED.  Considered simply sending the output to the
>> serial port and letting a computer read the details.  And that really omits
>> the time factor, although I could do a 0V -> 5V step and observe the time
>> it takes, I guess.  Overall, too complicated, so I never tried to implement
>> it.
>> I do have a bunch of Silonex Vactrols that would be nice to
>> characterize....
>> Pete
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