Measuring Sense Resistor On Current Source

[Instro_Spark]

Hey dudes was hoping someone can point me in the right direction i've attached a PDF with my schematic.

As the title says i'm trying to measure the volt drop across a sense resistor (R10 in schematic) which produces a 2.048VD when its drawing 4mA and 10.24 when at 20mA

So how would i go actually measuring this VD then scaling this to range which can be feed to a microcontroller.

Any ideas to improve this circuit is always welcome im learning just a bit more day by day so cool.

[Strada916]

Voltage divider. Simply put a 1M pot across the 512R resistor and use the wiper as input to the mirco. Adjust pot until you get 5V or 4.096 at 20mA. The 1M pot will effect the total 512R resistor by about 0.3R ohms law 1/((1/512R)+(1/1M)) = 511.7R

[Instro_Spark]

cheers for the response mate sounds easy enough since i have a spare opamp is there a way to use this to measure r sense resistor

[Psi]

You could use the voltage divider (as said above) and feed that signal into your spare opamp configured as a buffer.
This will convert the high impedance voltage divider signal into something within spec of your MCU's ADC input impedance (usually they expect 10k or less for full resolution).

[Instro_Spark]

Awesome thanks for your input fellas all the best

[Instro_Spark]

actually another question would i be able to get away with not using the second op amp from the left thats config as a voltage follower its going from a low impedance output into a high impedance input or am i way of the mark

[Psi]

yep, it's not doing anything

You already have a low impedance source from the opamp before it, so it isn't doing anything.

[Instro_Spark]

awesome haha sorry another question when setting up gain for your op amp are you better of using higher value resister at the moment im using 10k and 2.5k but i could also use 40k and 10k to get the same gain im guessing that with lower values there would be more current to flow but does using higher value resisters  introduce any noise issues