[sdiy] THAT 2155 on sale

Laughing Man laughingman647 at gmail.com
Sat Apr 11 04:53:46 CEST 2020

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>

> 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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