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
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!!
