Differential Inputs for cpfLoggerLite

[Ralf]

After building successfully my prototyp AVR Version of the
cpfLoggerLite (see this thread: cpfLoggerLite )
I am currently designing a version with full Tx/Rx RS232 and
4 differential Inputs. For Using differential Inputs with
the cpfLoggerLite here are my "break offs":

And here the Layout (not testet only a suggestion, I build
it up on a bread board for testing only)

I created the schematic and the layout with the free version
of eagle. If anybody is interested here are the schematic and
the layout:

Schematic
layout

I used the LM358 because I had some laying around. Be aware that this OPA is not a Rail to Rail and therefore the maximum output voltage is V+ - 1.5V. For my cpfLoggerAVR design I am
looking after Rail to Rail OPAs. If anybody does know a good one please let me know ...

edit:
Just found the LT1366 available at reichelt in germany, but for about 5EUR/pcs.
But this one would go rail to rail ...

Cheers for now
Ralf

 

[djpark]

Ralf,

It is a wonderful front end for the measuring the current flow with a sense resistor.

Can I suggest that the voltage at pin1 of J2 is also fed back to J1 for ADC to measure so that while measuring the current flow, the source voltage can also be measured.

Or for temporary arrangement, can we join pin4 of J2 to pin1 and join pin3 to ground so that we can read the voltage from pin3 of J1?

-- dj

 

[Ralf]

dj,

You can as well measure voltage with differential inputs;
I suggest to measure with the differential the current and
there are still one single ended input at the cpfLoggerLite
to measure Voltage.

Sometimes you would like to measure voltage over e.g. a luxeon,
but the output of the regulator is not grounded, here you could
use the differential inputs as well.

The layout was only a suggestion as I built the thing on a breadboard,
therefore a rewiring is still possible ...

Cheers
Ralf