[time-nuts] Poor man's oven

Bob kb8tq kb8tq at n1k.org
Tue Jun 6 14:27:03 EDT 2017


For a variety of reasons, if you go the MCU ADC route, put an op amp in between the
thermistor bridge and the ADC. It takes care of a whole lot of issues. 


> On Jun 6, 2017, at 12:13 PM, Adrian Godwin <artgodwin at gmail.com> wrote:
> The specs for the ADC are pretty vague : most of the errors are around 2
> LSB but all are quoted with vref at 4V. If you reduce vref (there's an
> internal option of 1.1V) you'll increase gain but some of those errors are
> going to stay physically the same. In general, I'd tend expect to get more
> precision but also more noise. Averaging may help a bit.
> On Tue, Jun 6, 2017 at 3:00 PM, Riley, Ian C CTR NSWC Philadelphia, 515 <
> Ian.Riley.ctr at navy.mil> wrote:
>> Chris,
>>> The trick with using a uP and it's built-in A/D converters is scale.  You
>>> want the limited 10-bits of revolution to fall over the operating range
>>> which is very narrow, like 1C.   Anything outside of that is either 0000
>> or
>>> 1111 and only seen at start-up.,  So at start up the the controller is on
>>> "bang-bang" mode then later you have milli-degree resolution over your 1C
>>> range.   Basically you are measuring noise. but your $2 uP can take
>> 100,000
>>> measurments per second and putt tour a digital filter.
>> I have seen but not used the AREF pins on Arduino and similar uPs; as you
>> lower AREF, do you lose any sort of accuracy? Is there a practical minimum
>> for what voltage you can feed into AREF?
>> -Ian R.
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