Little PICs with hi-res A-D ?

Me ? A PIC ? You must think I'm going mad !

No, it's for someone else I may work on a project with and he's into PICs. He wants a little 8 pin jobbie with an onboard A-D. Currently he's looking at a 16F220 IIRC. That only has an 8 bit A-D.

I reckon we need 12 bits off the top of my head but 16 would be nice.

Any suggestions ? I'm totally unfamiliar with their range and he's off on dog-sitting holiday for 2 weeks.

Graham

Reply to
Eeyore
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Selection table for 8 piners:

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12F683 is the pick of the bunch:
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only 10bit ADC, Microchip haven't figured out how to do 12 bit yet.

Dave.

Reply to
David L. Jones

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I agree, that's the best 8 pin PIC I know of. Don't be fooled by the 12F, it's still a 14 bit core like the 16F series.

Reply to
Anthony Fremont

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How about a couple with 'windowing' ? Can that be done to extend the resolution ?

Graham

Reply to
Eeyore

Eeyore wrote in news: snipped-for-privacy@hotmail.com:

Don't think anything up to 16F has anything better than 10 bits. Use an I2C A/D chip. The drivers are all over the place.

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Scott
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Reply to
Scott Seidman

Any particular recommendations ? Cheapish would be nice.

Graham

Reply to
Eeyore

Eeyore wrote in news: snipped-for-privacy@hotmail.com:

I've used the Microchip MCP3208, 8 channel 12-bit SAR with an SPI interface.

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16-pin DIPs are available. Less than $5 in small quantities. I think you need 4 bits to interface to it, so plan accordingly. I2C uses one less bit, if I recall.

Samples are free, and tend to arrive in 1-2 weeks.

There's a SAR selection page at

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10&lang=en&pageId=79

They also have dual slopes and sigma-deltas.

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Scott
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Reply to
Scott Seidman

LOL @ 2.7V. They really don't want to make life easy for you these days do they ? Oh well, it'll interface to a 10F220 at least ! Just hope everything else likes 2.7V !

Yes.

Thanks for the tip.

Graham

Reply to
Eeyore

I guess you could try oversampling. If you really need more than 10 bits, maybe an external chip? You really haven't provided much information on your ADC performance requirements.

Reply to
Anthony Fremont

I think you mis-read - it works from 2.7 to 5.5v

Reply to
Mike Harrison

Doesn't need to be fast for one if that's what you mean. It's for scanning some level controls on a pro-audio product. That's why we want better than 10 bit resolution. You might be wondering why but have you ever heard of a phenomenon called 'zipper noise' ?

I also looked the LPC700 and 900 series. They can do 12 bit which may be OK. There are some other factors involved too so a little chewing over is going to be required plus buying an EVM from TI (thankfully sensibly priced) which will be the gain control element (basically a smart MDAC with stunning performance).

Graham

Reply to
Eeyore

Not remotely what you are asking for, but the MSP430 16-pin parts can be as tiny as an 8-pin DIP and you can get them with 16-bit delta-sigma ADC.

Could also consider the PIC24HJ12GP201 in an SOIC-18 with 12-bit SAR ADC.

Reply to
Spehro Pefhany

Aha ! Yes I was wondering whether there might be something more interesting along those lines. I was wondering AVR too.

What do you program MSP430s in ? Noting that I'm no fan of assembler although the other guy probably would be OK with that.

I'd go LPC 700/900 myself instead for 12 bit.

Graham

Reply to
Eeyore

Look at some of the Linear SMB/I2C ADC's, they are a bit pricy but better than what you can do in a small PIC.

Cheers

Reply to
Martin Riddle

Eeyore wrote in news: snipped-for-privacy@hotmail.com:

Can't integrate the step response on the output? Something similar was done on the control signals of Yamaha gear. Worked fine except they overdid it and made it sluggish. Unless you also notice discrete steps when not actually stepping the resolution might be fine, just needing smoothing of changes.

Reply to
Lostgallifreyan

It's not driving a VCA.

Yes quite ! That's no good here, needs to be 'real time'.

This needs to be used for actual mixing so the steps need to be tiny.

There's several possible solutions including full DSP but that's more work.

Graham

Reply to
Eeyore

Eeyore wrote in news: snipped-for-privacy@hotmail.com:

Ok, but zipper noise is an output thing, so no go on analog? (Doesn't sound like DSP is needed, and I don't think it can fix this). What's it driving? I might not know an answer but I can give it some thought even if just to understand for myself. As I see it, the smaller the steps, the easier it is to filter adequately without it being sluggish. The idea of zipper noise affecting an input is passing strange, but if it happens, then dither.

I see that making extra work is best avoided by lots of small steps, but if this zipper noise is an audible thing to fix then it must be possible to do it with analog parts. Got to be some timing of a simple filter that ought to help, whatever it's driving. If it can suppres the audible click of a DC change of 1/256th of the dynamic range jumped in one snap, it should work, and be fast enough for real time. How fast CAN a mix engineer move a knob? :)

Reply to
Lostgallifreyan

Eeyore wrote in news: snipped-for-privacy@hotmail.com:

Don't use pots for input-- use encoders. Then the resolution of each step is whatever you program it to be. You can even program speed sensitivity, or course and fine adjust.

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Scott
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Reply to
Scott Seidman

Can you hear the difference between steps at 8 bits? Or see it on a scope that isn't looking at a test tone? How about 10 bits?

Is the problem the static step size or the jumps between steps? I assume the latter from the name. If so, I'd expect you can do something to invent fake sub-steps on the input side at reasonable times and the output side would do whatever it would do if you had an input with more real bits.

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Reply to
Hal Murray

Mastering equipment.

Very fast.

I have just suggested an analogue solution in fact. It seems like one guy got over excited about some clever looking MDACs that on detailed reading of the data sheet aren't so clever after all.

Graham

Reply to
Eeyore

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