Electronics > Beginners
Spice me up this Schmitt trigger
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soldar:
Rummaging through my files I discovered this Schmitt trigger which I designed over twenty years ago, I seem to recall it was for some alarm system, quick and dirty.

Now I wonder if it really works as I wanted it to.  The transistors were just generic small signal and the diodes also generic small signal, like 1N4148.

I do not have any simulation software so if anyone would like to model it and let me know if it performs correctly and/or any observations or improvements.
iMo:
I would highly recommend you to download the LTspice, it is free and easy to use.
It takes you a few minutes to draw and simulate.
soldar:

--- Quote from: imo on January 12, 2019, 01:28:57 pm ---I would highly recommend you to download the LTspice, it is free and easy to use.
It takes you a few minutes to draw and simulate.
--- End quote ---
Thanks imo! So it does seem to work. I see you simulated removing the diodes and now I remember I added them to raise the voltage of the switching points.

I am still using Win XP Pro SP3 so I downloaded LTSpice IV, version 4.23l. I do not know if files created with later versions would be compatible but may be you can post the file for this circuit and I can try to open it.

I will have to do some learning now. Thanks for the tip.

E.T.A.: I opened one of the example files. I see they use the extension .asc which in my system is already taken by PGP keys but I guess that's not a major problem. I'll have to work around it.

Here's a tip for graphics: this type of graphics are much better compressed with PNG than with JPG. The graphic is crisper and the file much smaller in size. JPG is really only appropriate for photos and similar graphics.
Zero999:
The circuit can be simplified to some extent.

Regarding the graphics, yes PNG helps make it smaller sharper. I just paste the schematic and plot into Gimp and reduce the colour depth to 256 colours or less to save space/bandwidth.
soldar:

--- Quote from: Zero999 on January 12, 2019, 02:49:41 pm ---The circuit can be simplified to some extent.
--- End quote ---
Yes. I think mine would be more robust against transients. As I said, it was for some kind of alarm and the input was by way of a long loop and you have to be careful with induced transients. I probably added a capacitor at the input.
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