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.
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.
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 !
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.
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).
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.
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? :)
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.
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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These are my opinions, not necessarily my employer\'s. I hate spam.
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.
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