gEDA-user: temperature logger/sensor

[Levente Kovacs <leventelist@xxxxxxxxx>]

Hi,


In the last few weeks, I've been busy designing and bulding a temperature
sensor/logger. The second version is out and can be found here.

http://logonex.eu/~leva/projects/temp_collector/

There are a few pictures of it.

http://logonex.eu/gallery/tns/1043.html

There is no firmware yet, I am planning to write it in the coming week.

Originally, I was asked to make some temperature logger, which logs the data
of samples taken every half 30 minutes in a half of a year. I planned using
KTY temperature sensors. However, if you change the gain of the INAs you can
use it with PT100 sensors. I am planning to replace my reflow oven design with
this circuit. BTW INA. I know that one can buy INA in a single IC, but, AFAIK
they are quite expensive, and they are too sophisticated for this application.

It is equipped with I2C eeproms to store the recorded data. The RTC with the
supercap maintains time and date data even with power supply loss. I am
thinking to use a battery instead of the supercap.

The power supply gives me lot's of head scratching. I placed a 470pF capacitor
to produce the 50kHz switch frequency, but according to my measurements it is
only 6kHz. I replaced the cap, but stiill the frequency is low. Despite this
fact, it is working good, and it has only 30mV ripple. If anyone could give me
a hint what is going on here, that would be fine. In my first sample, I used
the same circuit, with the same cap, and the frequency was 50kHz. Very odd.


Cheers,

-- 
Levente Kovacs
http://logonex.eu



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