[time-nuts] Poor man's oven

Bob kb8tq kb8tq at n1k.org
Tue Jun 6 16:37:27 EDT 2017


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. 

Op amps are cheap ….


> 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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