[time-nuts] Poor man's oven

[Bob kb8tq]

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 <jimlux at 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 <jimlux at 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.
>>> 
>>> 
>>>> 
>>>> 
>>> 
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