ADC Calculation Help

[ericgibbs]

Ok. Lets see if I have this right.

R3 will be another Isense resistor, for the "display unit"

U1 will be used to amplify the voltage from the Isense resistor, outout to ADC.

R1/2 acts as the voltage divider from the output, driving U2 acting as a buffer to the ADC.

bit confused about 1.3V referance that is fed into U1/2

Thanks

Did you see the latest schematic in my edit.??
Its uses R7 to make the circuit simpler.
The -1.3V is already available in the original circuit.
The buffer is needed on the divider as the adc expects an input impedance of less than 10K

 

[Lighty]

I'm with you now. Though we where going to leave connecting directly to R7 as you thought it was unstable.

So its basically only 3 take of point on the board, -1.3V, Gnd and V+ out.

I suppose I should just tap off the + rail to drive a LM7812 for the OPA.

I'll try get all components tomorrow to bread board it. I will keep you up to date!

Thanks Eric!

 

[ericgibbs]

I'm with you now. Though we where going to leave connecting directly to R7 as you thought it was unstable.

So its basically only 3 take of point on the board, -1.3V, Gnd and V+ out.

I suppose I should just tap off the + rail to drive a LM7812 for the OPA.

I'll try get all components tomorrow to bread board it. I will keep you up to date!

Thanks Eric!

hi,
Its important to note that most rail to rail OPA's have a maximum supply voltage of +5.5V, for the this type use a 5Vreg not a 12Vreg.
Lets me know which OPA you buy.