<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div style="color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br class=""></div></div></div><div><blockquote type="cite" class=""><div class="">On 10 Apr 2020, at 16:17, Pete Hartman <<a href="mailto:pete.hartman@gmail.com" class="">pete.hartman@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div dir="ltr" class=""><br class=""></div><br class=""><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Apr 10, 2020 at 8:43 AM Oren Leavitt <<a href="mailto:obl64@ix.netcom.com" class="">obl64@ix.netcom.com</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div class=""><p class="">I have an idea for "quick matching" photo cells.</p><p class="">Basically one op-amp - a comparator with hysteresis (like that of
a basic LFO)</p><p class="">1) Put the photo cell side in a resistor divider and connect to
the comparator input.</p><p class="">2) Connect comparator output to to LED side thru appropriate
current limit resistor.</p><p class="">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.</p><p class="">An idea..</p></div></blockquote><div class=""><br class=""></div><div class=""><br class=""></div><div class="">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. <br class=""><br class="">I do have a bunch of Silonex Vactrols that would be nice to characterize….</div></div></div></div></blockquote><br class=""></div><div>Why not give the Arduino a DAC for output and then use that to drive X/Y channels on your oscilloscope. The X channel only needs to be a simple scanning ramp (so a basic incrementing count to the DAC) and then the Y channel displays your response value.</div><div><br class=""></div><div>Tom</div><div><br class=""></div></body></html>