Adding voltage to a circuit

[Tobias]

I want to add voltage to the output of a potentiometer using a PIC and a digital POT. For example the output voltage of the POT is 2.3V and I want to add .1 to 2Vs to that signal. Any ideas? I have tried using the Pots output tied into one side of the digital pot and having 5vs on the other side of the digital pot. Doesn't work to good.
Thanks in advance
Toby

[mister_e]

Summing amplifier made with an opamp?

http://www.daxia.com/bibis/uploadasp...2%B7%CD%BC.pdf

OR, pot goes to PIC a/D input, it calculate the final voltage, and generate the according voltage with full resolution PWM or DAC. Still possible to use digital pot.

[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