my frequency adjuster

[mstechca]

I am able to fine tune the frequency by pushing a button, and using the 4040 binary counter.

In order for me to obtain good steps, I must place some capacitors in parallel, and some capacitors in series, because there is no store that sells capacitors in exact multiples.

I want capacitance to be from 1 to about 16 pF.

If I were to use single capacitors, then the bits in the counter (if I only use 4) will be as follows.

Bit 0: 1.2pF
Bit 1: 2.2pF
Bit 2: 4.7pF
Bit 3: 8.2pF

Here's the problem. When counting, I want to see:

1.2pF, 2.4pF, 3.6pF, 4.8pF, 6.0pF.... and so on.

According to the bits above, I would get:

1.2pF, 2.2pF, 3.4pF, 4.7pF, 5.9pF, 6.9pF, 8.1pF, 8.2pF.... and so on.

As you can see, the count is uneven.

Are there any better capacitor values that suit this application?

I want the even-most count without making my circuit consist of 99% capacitors.

 

[bloki]

Maybe you can use cap trimers or varicap diode with adjusted voltages selector.

 

[mstechca]

thanks, but using varicaps will require me to buy specialized tools to measure capacitance, and I don't use varicap diodes. They are more expensive.

 

[bloki]

You do not need to measure capacitance but only frequency. Actually you have to set correct frequency for each step by potentiometer.

 

[Russlk]

Where are you going to find 1 percent caps in this range? You would be better off to invest in a $50 cap meter and use trimmers which are easy to find in this range.