Hi The Freescale ADC’s are pretty good compared to a lot of other MCU ADC’s. They still are not as good as you might think from the audio ENOB numbers. Something in the 10~11 bit range is doing quite well at DC in a control loop, even for them.
Bob > On Jun 6, 2017, at 8:12 PM, jimlux <jim...@earthlink.net> wrote: > > On 6/6/17 1:37 PM, Bob kb8tq wrote: >> Hi >> >> Often when you dig into the details of MCU ADC’s they have a little note >> “optimized for audio” or >> “not recommended for control loops”. It can be a bit of a head scratcher to >> work out what they are >> getting at. The big issues in this case seem to be DC leakage and 1/F noise. >> Yes, they do sort of go hand in hand :) >> You need to be willing to check out the ENOB at DC in order to use them >> effectively in a simple >> OCXO setup. That or be willing to flip the bridge ends on demand and try to >> cancel out the issues. >> Unfortunately that adds both complexity and a string of other fun and games. >> > > This one seems to be designed specifically for this kind of DC measurement, > sure, it will sample at 100kHz, but not with the amplifier and averaging and > such. > > Its based on the Freescale (now NXP, I guess..) Kinetis K20 series > > It has a bewildering variety of peripherals (touch sensors, etc.), as well as > the usual multiple UARTs, SPI, I2C, timers, counters, etc. What's nice is > that PJRC (who make the teensy series) have written all the drivers and > libraries to integrate into the Arduino environment for those that don't live > for decoding the 1000 page processor family manual and 600 page package > specific manuals that give the specific pinouts and options on the one YOU > have in front of you. Your "time to first light" is much shorter. And then > you can hack away. > > I think this is more a chip designed for embedded controllers and the like. I > don't know if it has the processor and peripherals to do, say, 3 phase > induction motor control or Ultrasound processing, but it might. > > The Atmel processors are nice (and you can actually get one of the Arduino > flavor ones in a rad hard version.. for those "control the device in the > beamline" applications), but the Kinetis are easily an order of magnitude > better - no bit banging to do serial protocols, USB built in, decent ADC, > floating point, etc. > > > > >> Op amps are cheap …. >> >> Bob >> >>> On Jun 6, 2017, at 3:54 PM, jimlux <jim...@earthlink.net> wrote: >>> >>> On 6/6/17 11:47 AM, Chris Albertson wrote: >>>> Yes, as I wrote. I would not mess with AREF. At most you can only get a >>>> multiplication about 4. Use an op-amp. Signal conditioning really >>>> almost alway is required in the analog domain before any A/D conversion >>>> >>>> Also like the uP is not inside the oven and has a cable of some length so >>>> you'd want a buffered analog signal on the cable, the op-amp can do that >>>> to. >>>> >>>> Those $2 parts I linked to have the ADC referenced to 3.3 volts but have 12 >>>> bits as compared to the arduino which has 10 bits >>> >>> >>> or use a Teensy with a 16 bit differential input ADC. Arduino compatible, >>> cheaper, yeah, you probably get 13 bits real performance from the ADC. >>> Also has a real analog output (not PWM and a LPF) if you need that. >>> >>> Programmable gain, sample averaging in hardware, etc. Not bad for <$20. >>> >>> >>>> >>>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
