Frequency to Pitch voltage conversion?

Andrew M wrote in news: snipped-for-privacy@4ax.com:

Thankyou. I'd quoted points you made in two other posts but never thanked you directly yet. :)

This being the subthread where people have grasped what I want, I'll restate my request in non music-related terms, as doing that has caused a LOT of confusion..

I need a fast DC log converter that will do base 2 log output with accuracy to within 5mV/V on its output, over a range of 5 doublings of input volts. It needs to be a single IC, preferably an 8-pin DIL, with very low thermal drift, and to be as simple to use as an op-amp.

I'll look at the log-amp search suggestions I've been given, but as this is a problem that goes far deeper than a newby with a search engine is likely to handle, I'm still hoping that someone who uses these devices might have some parts suggestions to make things easier.

If there is a standard part equally simple to use, that takes a regular pulse train input to make a frequency-to-log-converted-voltage digitally, outputting a voltage with 14 or 16 bit accuracy, this will also be an ideal answer. This part has to have very low thermal drift.

so what i gather here is you want a fixed output frequency with in a given window of input freq/Voltage? for example if you had a 100..200 hz input you would like the output to stay at 150 hz for example? and then step to the next level for example 201..300 input to give you a 300 hz out ? is this correct? this is what i call a stair case output. anyways, i am just about to give up on this.. but from what i gathered, you mite want the output to to do this with a Voltage input that you can vary and the output will simply stay with in the case window until the input range gets high enough to switch to the next level?

sometimes called an Octive generator for tuning instruments. but normally they use a switch the select the output.

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Looked at some of my old (1976) analog books. The AD755N is one such animal, also look at 752, 751 and 756. Don't know if Analog Devices still exists, but those parts sure show up on search. AD755P in the PNP version. My 1976 book list price AD755N (1-9) $55, (10-24) $49, hope the price didn't inflate!

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"flexten" wrote in news: snipped-for-privacy@i40g2000cwc.googlegroups.com:

Great stuff. :)

Looking for 755N or 755P got me some leads. Those things look like they might be old hybrid modules, maybe not made now. (I also wondered about AD, having read something somewhere. I hope they haven't demised).

I found this page:

It's probably going to go quickly beyond my grasp, but I'll read closely, it looks like a good one.

I also came across a Texas Instruments 'LOG100'. I don't know enough to make a good choice though, so any input still welcome. :)

I was wrong about my accuracy requirement, btw, is actually 12 times more, I was thinking of semitones not the whole octave, so I need within 400µV/V.

What amazes me is that this doesn't seem to be a standard part. The 741 and many other op-amps are, and are made by many firms, so there's no chance of easily losing access to new ones. I'd thought (and hoped) that log amps would be almost as easy to find as linear ones.

Yeah, these slow chips seem to be called "computation chips" nowadays. Everything i see is mostly RF stuff, GHz. Anyway at AD they have a section on log amps and one on computation chips. The 755 was nice in it's day but may be hard to find, yes, probably LSI. Digikey has catalog of Analog Devices with names behind part numbers, the AD site is impossible to find stuff.

Best

One final post for me. So maybe the AD538, LOG100 or MAX4206. I see the LOG100 is stopped production yet looks good. I like the MAX part also.

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"flexten" wrote in news: snipped-for-privacy@e56g2000cwe.googlegroups.com:

Thanks for that. :)

I'll look at those three. This stopping of production bothers me..

Maybe there might be something digital entirely self-contained with 16 bit I/O, seen by the user as voltages in and out. If there isn't, there might at least be some cause for it. :) If these chips were as easy to use in analog circuits as op-amps are, I think the general uptake might keep them in use. Still, I've learned that there is enough use in light measurment for it to be relatively easy to find something.

That MAX4206 is still a lot harder to use than an op-amp. If I could get simple volts in, volts out with high resistance input, low resistance output, I'd be happier.

Anyone got a cheap PICBASIC setup? :) I might just have to get into that to solve this thing, if a PIC with inbuilt 16 bit DAC exists.

"flexten" wrote in news: snipped-for-privacy@e56g2000cwe.googlegroups.com:

I found a datasheet for an AD8307.

8-pin DIL. Looks like it takes volts in directly, not current, and puts volts out.

It might be ideal, but I have NO idea if it is. They say that it has a bandwidth from DC to 1 GHz, and that it can be used for DC purposes, but that datasheet reads like an Open University program on advanced RF and AC systems. How this is going to be as easy to use as an op-amp, I don't know. Op-amp's seem to have some very simple starting points to grasp, but this thing seems to start in exalted levels of complexity that leave me cold. There's nothing there that gives me any idea of how it will work on DC signals, let alone whether it will give me the accuracy I want for 100 cent tuning accuracy in voltage control over 5 octaves (I'd settle for three).

I doubt it. Your application - especially with the accuracy constraints you've quoted - is spectacularly obscure, & is the type of function that's usually embedded within electronic musical instruments in the form of a chunk of DSP code. I'd be astounded if it were possible to meet your requirements with a reasonably sized & priced analog circuit, & doubly so if there was a standard chip meeting your spec's. If it were me, I'd use the smallest single-chip embedded controller I could find that has an A2D & a D2A converter (possibly one of the smaller PICs) & do the whole thing in software.

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Sadly, I strongly suspect that it's the simplest answer you're going to get.

12 bits of accuracy is extremely difficult to achieve in a completely analog, DC-coupled signal chain - especially if you need to perform transfer functions of the sort you've described. Even single opamps with that sort of accuracy are somewhat exotic, & I can't think of any complex function analog chips that even come close.

You seem to be pretty determined to go with an all analog solution, but I really think that it'll prove to be a blind alley, & you'll end up having to either give up your project or go digital to get a workable solution.

--
   W          
 . | ,. w ,   "Some people are alive only because
  \|/  \|/     it is illegal to kill them."    Perna condita delenda est
---^----^---------------------------------------------------------------

Lionel wrote in news: snipped-for-privacy@4ax.com:

ok :) I think I need to find a cheap copy of PICbasic, hopefully from someone who's decided they don't want to use theirs..

While the market for a ready-made IC as you describe might be small, there is definitely enough of a market to make a bit of money from it. I might ask Dieter Döepfer if he's considered stocking a few for hobbyists who want to adapt his or other maker's modular gear.

Lionel wrote in news: snipped-for-privacy@4ax.com:

Ok, I agree. I wanted to see what other's thought so I pushed at this the best way I knew, ask instead of trying to invent intractable wheels.

As a last grasp at an all-analog idea, I have one question:

Could the AD8307 by worth playing with as a DC log amp for three octaves worth? For some uses I can relax accuracy restrictions, in one case it only has to be close enough that whistling a note be tunable to the right pitch by listening to the final output through headphones. So long as it's not off-tune by a semitone or more, it might be possible to make up for errors by practising with it. So long as the thing makes a consistent DC log scale conversion, it might do. I can't tell from its data sheet because it's all about AC and RF performance, and I'd learn faster if someone who knows about that IC could tell me. :)

I decided to look at PIC chips. It won't be quick but it will get me there, and get me to other things too.

As a last grasp at an all-analog idea, I have one question: (repeat of earlier unanswered post..)

Could the AD8307 by worth playing with as a DC log amp for three octaves worth?

For some uses I can relax accuracy restrictions, in one case it only has to be close enough that whistling a note be tunable to the right pitch by listening to the final output through headphones. So long as it's not off-tune by a semitone or more, it might be possible to make up for errors by practising with it. So long as the thing makes a consistent DC log scale conversion, it might do. I can't tell from its data sheet because it's all about AC and RF performance, and I'd learn faster if someone who knows about that IC could tell me. :)