[time-nuts] Poor man's oven

Chris Albertson albertson.chris at gmail.com
Tue Jun 6 14:47:54 EDT 2017

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

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

The next step up the complexity scale would have you place an I2C
interlaced ADC inside your oven.  These don't cost much and have several
ADC channels.  then your oven has full digital interface and a much higher
quality DAC.  But this adds another 2 or 3 dollars to the design.   Maybe
worth it as now all the analog stuff is inside a temperature stable metal
tin can.     But you have to watch this feature-creep as you can drive up
cost with little to show for it.

Also I'd not want the analog stuff designed to work only with ADC built
into one specific development board.  The I2C serial interface is pretty
much universal

I'm thinking something like this:
Notice that the chip has programmable gain, it can scale the input over a
small range before sampling.
For $2 it's still a "poor man's part and you do NOT need to make a PCB to
use it.

On Tue, Jun 6, 2017 at 10:08 AM, Jim Harman <j99harman at gmail.com> wrote:

> On Tue, Jun 6, 2017 at 10:00 AM, Riley, Ian C CTR NSWC Philadelphia, 515 <
> Ian.Riley.ctr at navy.mil> wrote:
> > Is there a practical minimum for what voltage you can feed into AREF?
> >
> It is hard to find on the data sheet, but the minimum voltage for an
> Arduino's AREF is the internal analog reference voltage - 1.1V for the Uno,
> 2.56V for the Leonardo or Micro. The 32U4 chip in the Leo and Micro has
> options for differential analog input and gains of 10, 40, or 200 but they
> are not supported by the Arduino IDE - you have to set the internal
> registers directly to use them. Also the input amplifier is pretty slow.
> --
> --Jim Harman
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Chris Albertson
Redondo Beach, California

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