Stupid Q: R and C values for a Schmitt trigger oscillator

[markusw]

How do you calculate the R and C values to run a CD40106 at a given frequency (like in R.G.s sequencer)? I have looked through the data sheets but I can´t figure out how to do it. Thanks for your help.

Markus

[bobbletrox]

The formula can be found on this site:
http://www.interq.or.jp/japan/se-inoue/e_ckt13.htm

(I have no idea how to do it though!)

Is it just me, or has the forum got sequencer fever?  

[maximee]

no bobbletrox...i have the same feeling....and i think that we two kind of started it

[Arno van der Heijden]

Also, look here:

http://www.electronics-forum.net/design/how_to_det_freq_of_schmitt_oscillator_326334.html

[Arno van der Heijden]

And here:

http://www.ece.concordia.ca/~a_mozgov/main.php?pg_num=42

[markusw]

Thanks a lot! After browsing through all these links the f=1/RC formula seems to be a sufficient approximation. When using the larger formula containing the + and - treshh. voltages, f values change quite a bit depending on whether you use  the min, max or typ values (e.g using the typical values for CD40106 at 10V VDD the formula looks like f=1/RC*1,5) So, if I got it right, the exact f can´t be predicted since it depends on the exact properties of the chip in your circuit.

BTW: boobletrox, if I did the calculation correct you needed to go down with R4 in your http://users.bigpond.net.au/styrowfoam/eightstep.gif schemo to 4,7k in order to reach 10 Hz (maybe even lower when using the larger formula). Please correct me if I am wrong.

Indeed, there seems to be some kind of sequencer flu. I got caught by the "my Meatball needs a 4,6,8 step up/down/random" virus. So RG´s sequencer seems to be really fine. However, at the moment I can´t figure out how to switch to 6 steps.

Take care,

Markus

[bobbletrox]

BTW: boobletrox, if I did the calculation correct you needed to go down with R4 in your http://users.bigpond.net.au/styrowfoam/eightstep.gif schemo to 4,7k in order to reach 10 Hz (maybe even lower when using the larger formula). Please correct me if I am wrong

I used the values from Tim Escobedo's Ez-Lfo because I figured any Lfo with a decent range should work fine for controlling the tempo of a sequence.  But 4.7k gets it running within RG's specs does it?  Thanks!  I'll try that out.

[markusw]

In the Ez-LFO there is a 2.2 µF cap. So the frequency goes up to about 10Hz.