ADC Calculation Help

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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
 

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  • 0V-30V_modified_PS_latest.GIF
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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.
 
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