Adding voltage to a circuit

[Tobias]

Thank you for the input. I am going to go the Op-Amp route.

[Tobias]

Here is what I have. It seems to work good except that the digital pot does effect the value from the turn pot. Is there a diode arrangement I can use so the two turnpots don't work against each other. For example with the turnpot at 100% it reads 4.41v when connected to the entire circuit. When standing alone it reads 4.47v at 100%

Thanks for your input

[mister_e]

The non-inverting summing amplifier may cause that as the input current depends on the level of all the other inputs AND the effective input impedance is not constant.

Better to use a inverting configuration.

[Tobias]

HI
Attached is my attempt with the inverting op-amp. I must be out in the woods on the resistor values needed. Any ideas what I am doing wrong?
Thanks

[mister_e]

That's Sim results, or real results?

the Opamp Supply rails are not connected on your schematic though. You must use a dual rail voltage (+V, -V)

What available voltage rails you have available on your board now? (regulated and not regulated)

One thing is sure, as the OPamp pin 2 is considered as Ground, i would use higher value for R4, R5 to don't interfer the Pots impedances.

[Tobias]

Its from NI MultiSim. I looked around and found a basic three pin Op-Amp. The results were more like what I was expecting. Thanks for humoring my learning curve

[skimask]

That's Sim results, or real results?

That's gotta be a sim! And probably some smoke too!

EDIT: well...ahhh...too late...

[mister_e]

great sims

Did you already tried LTSpice?

One thing is sure, you really need a negative rail.