[time-nuts] temperature sensor
EWKehren at aol.com
EWKehren at aol.com
Tue Jun 24 20:19:40 EDT 2014
We use NTC 10K with the FRK. Precision is not important.We have to play
with the settings in order to have fan starting voltage over the full temp.
range.
Bert Kehren
In a message dated 6/24/2014 8:12:45 P.M. Eastern Daylight Time,
shalimr9 at gmail.com writes:
After having tried just about every solution under the sun, my opinion is
that within the ambient temperature range (up to at least 100°C) and
homebrew budgets, nothing beats an NTC thermistor.
They are inexpensive, have a large output and interface most easily with a
microcontroller's ADC in ratiometric mode requiring a single precision
resistor. Even cheap ones have a 1% tolerance which is more precision than you
will ever need.
My favorite is a 10k at 25°C with a B factor of 3380 at 25/85 that costs
$1.25 at Digikey. The math to derive the temperature from the ADC reading is
simple (you do need the log function) and a mundane 12 bit ADC gives you
temperature with a fraction of a degree resolution and much better than a
degree absolute precision if you actually needed it. With a 2.5V reference
(like those in my favorite Silabs uC), self heating is negligible, even in
open air (a fraction of a degree).
This is implemented in my Thunderbolt Monitor kit software to measure
ambient temperature.
If you need better resolution than what you can get by directly measuring
the voltage at the junction of the resistor and thermistor (due to limited
resolution of the ADC), add one op-amp and three resistors, or use the PGA
if your microcontroller has one.
Didier KO4BB
On June 24, 2014 6:43:07 PM CDT, Chris Albertson
<albertson.chris at gmail.com> wrote:
>On Tue, Jun 24, 2014 at 3:24 PM, Mark Sims <holrum at hotmail.com> wrote:
>
>> ...
>> However it is disappointing that no one has stepped up to tackle the
>> temperature problem.
>
>
>I can post what I have. It's a uP based PWM fan controller. It is a
>stand
>alone device that does not know anything about the FE5680 but it would
>be
>easy to add into any GPSDO using the GPSDO's existing uP provided there
>were enough extra analog pins available. It uses the Arduino software
>environment but I built it using a bare 8-pin DIP. The problem with it
>is
>I do not have a good temperature sensor, The ones I tried are noisy.
>SO
>I'm looking forward to your sensor info.
>
>My first controller used a comparator chip. Then I figured the uP was
>the
>same cost and same 8-pin package but could do things like PID, data
>logging, led status blinking and "whatever". This is a start on the
>code
>that works just like the comparator and uses a pot for the user to
>adjust a
>set point.
>
>If you see a way to make this better post the changes.
>Some things I will do are (1) use better sensor, (2) use PID library,
>(3)
>measure ambient air temp.
>FanController.ino
><https://dl.dropboxusercontent.com/u/28915695/FanController.ino>
>
>BTW is there any design info on the FE5680 controller. Schematics of
>source code?
>
>
>
>--
>
>Chris Albertson
>Redondo Beach, California
>_______________________________________________
>time-nuts mailing list -- time-nuts at febo.com
>To unsubscribe, go to
>https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>and follow the instructions there.
--
Sent from my Motorola Droid Razr HD 4G LTE wireless tracker while I do
other things.
_______________________________________________
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
More information about the time-nuts
mailing list