Schmitt Trigger frequency calculator

This post was flagged by the community and is temporarily hidden.


Is this what you are searching for?

1: R = 1.2 / (0.01 * 1E-6 * 820) = 146341

2: R = 1.2 / (0.01 * 1E-6 * 1150) = 104347

3: R = 1.2 / (0.01 * 1E-6 * 465) = 258064

4: R = 1.2 / (0.01 * 1E-6 * 317) = 378549


wow thank you so much ! you are a really genius !!

In how unities are the results ?? In Ohm ?

R is in Ohm, so e.g. no 1 is 146341 Ohm which is 146 kOhm and a bit.
But this is not a resistor value you can buy. You can however set a trimpot to this value. The easiest way is not to replace the trimpots but set them to the 4 values.


thank you !! :facepunch::pray:

I have convert all the values in Kohm and I go to replace the trimpots with approximate common resistors values.

but I don’t understand why he use only 100k trimpots because I have results that exceed this value…

1 Like

The CD4000 series thresholds aren’t that precise so that 1.2 is a “typical” value (or at least I think it is, haven’t derived it), and capacitors are usually ±10% or worse. If you want exact frequencies, you need the trimmers.

(also note that your schematics use 0.05 uF for the lower oscillators, which isn’t a standard value but you could use 0.047 uF (47 nF) and divide the resistor values by 4.7)


And there’s always our old friend the breadboard.


yes I would like to replace 50nf with 47nf capacitors but I didn’t thinking about modify resistors values… thank you for the tip !

So I need to divide each resistor IN OHM with 4,7 ??

thank you, great helpfull !!

in finally maybe I go to add the trimmers… but I’m so lazy and need more place on my protoboard ahah

p.s: I have see some Schmitt Trigger calculators who are using 0,8 rather than 1,2… how value look the more judicious ?

Keep in mind that if the supply voltage sags a bit then the hysteresis voltages will sag too and effect the tuning.

1 Like