[time-nuts] Poor man's oven

Van Horn, David david.vanhorn at backcountryaccess.com
Tue Jun 6 13:39:05 EDT 2017

You can feed in an external AREF, but look at the data sheet for the particular AVR chip.
One thing which is commonly ignored in Arduino-Land is the I/O pin leakage current and the maximum source impedance specs.
You are well advised to buffer the voltage you are reading, or make sure the source is low enough impedance that those errors won't get you.

All uCs have these issues, I just see this error made a lot in Arduino land.  My 3D printer is Arduino based, and uses a 100k thermistor driving the Arduino directly.
The community makes claims that a degree or two of temperature change is important, and yet the circuit isn't capable of that much accuracy.

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Jim Harman
Sent: Tuesday, June 6, 2017 11:09 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Poor man's oven

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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