This is my first INSTRUCTABLE.

So be kind, if I don't used all the steps in the right way.

As an electronic enthusiast, I often find myself of solving little problems like to make an oscillator to generate some specified frequencies.

For example I needed to build a bi-tonal tone, modulating an approximated 1kHz frequency with a 2,5 Hz frequency.

To do this I needed 2 oscillators and "mix" them in some way.

In this instructable, I won't show you the siren circuitry only the bitonal oscillator part.

## Step 1:

I immediately thought about the CD4069 hex inverter.

This "veteran" circuit enclosed, is nowadays a "standard" for many electronic thechnicians and can be found in books everywhere.

But how to calculate to get the component values and eventually make changes quickly without trial/error loops WHILE using some components one already has or are already available in the drawer ?????

I immediately thought to use a spreadsheet to make automated formula calculations ;-)

Enclosed is the excel file that does this, and enclosed IN THE FILE, are are ALSO some short instructions.

## Step 2:

I would like to ALSO reduce the component count so use a single chip.

I immediately thought about the CD4069 hex inverter.

This "veteran" circuit enclosed, is nowadays a "standard" for many electronic thechnicians and can be found in books everywhere.

But how to calculate to get the component values and eventually make changes quickly without trial/error loops WHILE using some components one already has or are already available in the drawer ?????

## Step 3:

I had available some 10KOhm resistor, so I planned to use them. I put these values into the R1 & R2 cells (C16 & C17). then I put the desired frequency in cell C27 in Hz.

The capacitor value needed appeared in cell G27 (in nF or nanoFarads).

I did the calculation for both sides of the oscillator, to get the 1,1 kHz and the 2,5 Hz I needed.

For the first oscillator (bottom IC side), 2 x 10 KOhm and 47 nF the predicted value was 1,188 kHz, the actual value was 1,113 kHz.

For the second oscillator (upper IC side), 2 x 10 KOhm and 22000 nF (22 uF or microFarads) the predicted value was 2,5 Hz, the actual value was 2,39 Hz.

The spreadsheet calculations worked like a sharm!!!!

## Step 4:

The spreadsheet calculations worked like a sharm!!!!

Into the spreadsheet you can do also REVERSE calculation, having R1, R2 and C.

Never forget all resistors values have to be inserted in Ohms and the capacitor values in nF (nanofarads).

If you use different values for R1 & R2, you'll get DIFFERENT duty cycles of the generated square wave, other than 50%.

For those who don't know what is on earth a "duty-cycle", quickly I can say it's the SIMMETRY of the generated square wave.

Never use this calculations for frequencies above some Megahertz.

For those of you "smart" on spreadsheet, whoud have already noticed the "adjust coeff's I added: those are for not having (eventually) DIV by ZERO! errors.

Feel free to redistribute the file as you like, providing not to remove the copyright.

Thanks.

I found it very useful, and hope could be useful to someone else too. ;-)