7555 pulsating led

[MrDEB]

designing a Statue of Liberty lapel pin for the 4th of July 2023'
have two similar schematics for a pulsating led (white 3mm led) but the capacitors are electrolytic caps that are larger than 3mm in diameter (have only 1/4 inch height restriction. THINKING of maybe using a titanium cap or? need to order parts but the capacitor size?
both of the schematics are basically the same.

 

[danadak]

This is for a blinky led, so I doubt accuracy matters much

I would agree for a throw away kind of device.

But goal was to avoid the Epilepsy problem, and in a crowd if everyone flashing at a different
rate that would be odd.

But to your point we do not know the over all OP criteria or goals, just a smattering.


Regards, Dana.

 

[danadak]

AnalogKid
I did a sim with an OpAmp as follows :

I moved one trigger edge 400 mV and got a period change of 170 mS on a rough period of 1 sec,
so if I move the other edge as well I am thinking tolerance >> 20% for sure. Note OpAmp allows
use of small cap, eg leakage << Schmidt. So if we go back to using Schmidt, and its leakage, we have
to use electrolytic and much smaller R, then we have its error to heap on top of this. And I have not
done V supply variation on top of all this.

Could be OP does not care if its once per year or once per uS then we dont care.


Regards, Dana.

 

[AnalogKid]

A 10 M resistor in a hand-built circuit? Fingerprint oil has less resistance and would shift the frequency.

ak

 

[Tony Stewart]

www.Falstad.com has written many cool magnetic, electronic & physics browser applications. The one I use all the time is the javascript version http://www.falstad.com/circuit/circuitjs.htm while the original one was Java based and is obsolete for many browsers.

It has dozens of built-in designs and many basic parts including arc gaps, motors, LED where you need to know how to choose the parameters. for 5mm LEDs , I use 2.1V @ 0.02A for 3.1V @ 0.02A then choose any color is just cosmetic with sliders. Drawing is much like LTSpice but simpler with rubber-band stretch on end points or vertical or horizontal by sweeping. and of course ^Z= undo with many other hotkeys. You can "export (design to a) link", then "create a shortcut" then "copy" it as I did above.

Mr. Falstad also has an analog filter app (passive & active) and a Fourier transform app with standard waveforms that you can play with in log amplitude and phase and then hear it.

 

[Tony Stewart]

A 10 M resistor in a hand-built circuit? Fingerprint oil has less resistance and would shift the frequency.

ak

if you can smudge a piece of epoxy with your fingerprints and measure < 10M I would be extremely surprised. They would have to be smeared in peanut butter. Of course, your fingertips still attached to the leads would alter R but that depends on pressure * area