Reccomendations for cheap data-logger?

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

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

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

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

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
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0.4W)

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!!

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

avr butterfly + carrier board

avr butterfly carrier board

avr butterfly code package for avr gcc

swr meter using avr butterfly

avr butterfly mp3

Or futurlec.com pic compact flash board

Would need to program the board

Alex