Using a 4016 to control a 555?

I'm in the process of designing a fairly simple square wave hexaphonic synthesizer using 555 timers, and want to be able to select the frequency of the timer using logic signals. Can a 4016 be used to select a resistor thus changing the frequency of the 555, or will it cause problems by dribbling a little current through or adding some resistance?

Thanks.

Hi.

You could use an Opamp voltage follower between the 4016 and the 555 to get rid of any high impedance from the 4016.

If you're looking to make music with this, I don't think it's going to be accurate enough. The variation of the 555 and caps, along with the 4016s might be too much. I'd worry about drift, etc. as well as the fact that you'll probably have to tune out initial errors for every note. But, it's worth a shot.

If it was me, I'd use 12 555s (or something else) for the 12 notes, and then run each oscillator through a 6-bit counter to get the6 sub-octaves. Now you've got 72 notes and you can use 4016's to select any of the 72 frequencies. Then you can tell people you've got a heptaconta-duo voice synthesizer!

barry said:

If you're looking to make music with this, I don't think it's going to be accurate enough. The variation of the 555 and caps, along with the 4016s might be too much. I'd worry about drift, etc. as well as the fact that you'll probably have to tune out initial errors for every note. But, it's worth a shot.

If it was me, I'd use 12 555s (or something else) for the 12 notes, and then run each oscillator through a 6-bit counter to get the6 sub-octaves. Now you've got 72 notes and you can use 4016's to select any of the 72 frequencies. Then you can tell people you've got a heptaconta-duo voice synthesizer!

Click to expand...

I should have been more clear about what I'm actually designing here...

It's meant to control as much like a guitar as possible. Six 555s, one for each string, with some very basic logic for selecting the highest held fret and using that frequency so you can do all the old tricks like holding down one fret and tapping another. Using only four frets + open string so you can at least play most basic chords.

I was thinking of using capacitor switching to change octave/add a capo, hadn't considered a frequency divider, will keep that in consideration, thanks.

Mega accuracy isn't hugely important. I have a tuning preset potentiometer for each string to fix the worst of it, and will be using 1% metal film resistors and very low tolerance polybox capacitors.

Prototyp_V1.0 said:

Hi.

You could use an Opamp voltage follower between the 4016 and the 555 to get rid of any high impedance from the 4016.

Click to expand...

That'd add a lot of complexity to what's meant to be a little bit of silly fun, but thanks for the suggestion.


After a bit of consideration, I've reorganised the design, using the 4016 to bypass resistors instead of select them. This simplifies the logic from the frets at least. Probably still going to have problems though right?

---------- Post added at 17:10 ---------- Previous post was at 16:45 ----------

Wait, I'm sorry, I missed what should be blindingly obvious here. No switching logic is needed at all if the switches bypass multiple resistors. I probably need sleep or something.

I expect, that you would want at least one octave with halftone spacing, so 12 switches per oscillator needed. Switch resistance of CD4016 (or better lower resistance CD4066) will still affect the tuning. Utimately, you need to fine tune each tone.

Small size is a priority over functionality here; going for something pocket-sized.

I've realised that I can do this without any "active" components at all by using switches to bypass multiple resistors, also emulating the guitarlike string termination I was after in the first place using logic gates. One of those things you put together using loads of technology and ideas and then realise afterwards "none of it was necessary"