Reccomendations for cheap data-logger?

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Folks,

Looking for a cheap data-logger for recording DC volts(0-40) on a
remote site.  I'm not looking for anything fancy, but I'd prefer a
reasonable memory and USB port. Weatherproof would be nice, but not
essential.

I'd prefer ready-to-go models, but would consider something that
requires (minimal) work to set up.

Any ideas appreciated.


Cheers,

Rod.....Out Back

Re: Reccomendations for cheap data-logger?



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Hi Rod - whats cheap?
Do you want self powered or is external pwr available?

A "Tiny  talk" logger in a 35mm film canister used to be a couple of hundred
$. You could stick a divider on the front end.

Check out Hastings data loggers (Oz)



rob





Re: Reccomendations for cheap data-logger?



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Rob,

Many thanks; I'll have a look at them in detail tomorrow.  However,
the few of the tinytalk units that measure voltage seem to only go to
25v max.

I'll probably need the unit to be self-powered, as the power available
at the remote site will be variable at best.

As far as cheap is concerned, I dont want to spend more than
$300-$400Au apiece. Dont know if this is going to get me what I want,
but I would like to think I can find something that suits.

Thanks again,


Cheers,

Rod.....Out Back

Re: Reccomendations for cheap data-logger?



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Rod - you can extend the voltage input range with a couple of resistors.
Making up a 2:1 divider from two equal value resistors (try 10k+10k? 0.4W)
will double the input voltage range of the logger. So a 25V max input logger
would work well. Range would become 0-->50V. Depending on how smart the
logger is, you may be able to configure it to the new range, if not just
double the values of the data logged after after you download it.
rob







Re: Reccomendations for cheap data-logger?



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Rob,

Yes; that'd work (only need a max of 40vDC, so 50V would be great).
Easy to double the results to get real voltage(if the logger cant be
configured). I might ring Hastings to see what the tinytalk loggers
are worth.

How do I connect the resistors to achieve this? (assume a simple sort
of lad here in electronics...).

Many thanks.


Cheers,

Rod.....Out Back

Re: Reccomendations for cheap data-logger?


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0.4W)
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logger




Rod, hopefully you can make out my sketch below.



0-50V in >------------
                      |
                      |
                     [ ]
                     [ ] 10k
                     [ ]
                      |
                      |-----------> 0-25V to logger input
                      |        |
                     [ ]       |
                     [ ] 10k   |
                     [ ]      ---
                      |       --- 0.1uF ceramic cap.
                      |        |
                      |        |
Ground   >-------------------------> to logger 0V / Ground



The resistors are in series, because they are equal in value half of the
voltage placed across the two resistors will appear across each resistor. ie
for 12V input you will get 6V across each resistor.
For 40V you will get 20V out.

A 0.1uF capacitor across the lower resistor may help if you find you are
getting noisy readings.

Not sure what odds and ends you have to build from - you could build it on a
3 wide bit of terminal strip, some strip board or even solder the resistors
together and then tack on the input, output and ground wires then heatshrink
it to prevent shorts etc.

Be careful - I assume the 40V may be from batteries / solar supply or
something - fit a low value fuse close to the voltage source just to be
sure, better to replace a fuse than replace wiring / fight the fire or
whatever......

At 50V you will have 25V on each resistor ==> 62mW power dissipated in each
R. So 1/4W / 400mW or whatever metal film resistors will be ok. Try to get
1% tolerance parts. Without knowing more about the source you are connecting
to or the logger input etc, I'd guess you'd get within a
one or two hundred odd millivolts of the true voltage value. If you want
better accuracy the easiest thing to do would be to measure the input and
the output with you multimeter and work out a correction factor that you can
apply to the logged data.

rob

PS - All care but no responsibility taken!!





Re: Reccomendations for cheap data-logger?


snipped-for-privacy@IHATESPAM.BIGPOND.COM says...
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Whats the required sample rate, ie How many readings per sec or minute ?

And

How many samples or what period do you want it to record ?

And

Do you need a trigger input,
ie. Only start logging if input voltage is between a certain range
or exceeds a certain value ?

And it might also be of interest to know how long the device
will be in the field before its re-acquired, though these days
that is not as much an issue as it can power down and retain
in non-volatile memory etc.

What are the environmental conditions, will it be in the sun
in the middle of the day or subject to moisture, splashed etc ?

--
Regards
Mike
We've slightly trimmed the long signature. Click to see the full one.
Re: Reccomendations for cheap data-logger?



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If you are prepared to break out the soldering iron , can program an avr
and have time.

avr butterfly + carrier board

http://www.siwawi.arubi.uni-kl.de/avr_projects/bf_logger/index.html
http://www.siwawi.arubi.uni-kl.de/avr_projects/bf_logger/robolog/index.html

avr butterfly carrier board
http://www.ecrostech.com/Products/Butterfly/Intro.htm0

avr butterfly code package for avr gcc
http://www.siwawi.arubi.uni-kl.de/avr_projects/#bf_app

swr meter using avr butterfly
http://www.qsl.net/kd1jv/digiswr.HTM

avr butterfly mp3
http://butterflymp3.sourceforge.net/


Or  futurlec.com  pic compact flash board
http://futurlec.com/CompBoard.shtml

Would need to program the board


Alex



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