Re: gEDA-user: temperature logger/sensor

[Levente Kovacs <leventelist@xxxxxxxxx>]

On Sun, 30 Nov 2008 21:57:41 -0600
Kipton Moravec <kip@xxxxxxxxxx> wrote:

> I probably would have gone with the Atmel Data Flash as opposed to the
> memory chips you are using. (But it uses SPI Interface.) For example:
> http://www.atmel.com/dyn/resources/prod_documents/doc3500.pdf
> 
> 
> As far as the Power Supply goes, replace the 470 pF cap. Either you
> accidentally put the wrong on on, or something is bad with the solder
> joint. Take what you have off, and put a new one on. Clean the board
> with Alcohol if you are using no clean or rosin core solder, or wash
> it if you are using water soluble solder flux.

Thanks. I replaced the cap, and it has the same effect. However, one of my
friend pointed out, that the regulator I am using maintains its switching
frequency as a function of the output current. The consumption is low.

> The other problem may be the C101 470 uF capacitor. Usually switchers
> need very low ESR capacitors in this position. So two electrolytic in
> parallel, or a Low ESR Tant. and add a ceramic 10 uF and 1 uF help
> ensure a low ESR with the big cap.  

That is a good point.

Thank you.

> Kip
> 
> On Sun, 2008-11-30 at 18:18 +0100, Levente Kovacs wrote:
> > 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,
> > 
> -- 
> Kipton Moravec AE5IB
> "Always do right; this will gratify some people and astonish the
> rest."
> --Mark Twain
> 
> 
> 
> 
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> 


-- 
Levente Kovacs
http://logonex.eu



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