Adding voltage to a circuit

[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.

[Tobias]

No I haven't, what do you think of it? I visited a friend last weekend who has MultiSim and downloaded the 30-day trial. Its pretty fun.

[mister_e]

Sims

I general they're all bull**** and useless... but someone has to make money with something huh?

LTSpice is free from Linear website (http://www.linear.com/designtools/software/index.jsp ). I used it few times already just for fun and evaluation. This is the only one i would trust if i don't have ANY parts on hand. MultiSim has to be good though.

If one day i find a real good Sim i would probably use it, 'till now... none has impressed me. Maybe good enough for education purpose or for proof of concept... but even simple stuff doesn't seems to work.

I always have the same test since day one, which i keep secret... ALL sim failed on. If one day one sim don't fail on, maybe i could says it's somehow useful. Why spend few thousands buck on something that doesn't work while you could have real results with real parts at fraction of the price?

The only useful one that cover almost everything is Proteus... but it's still useless... fun to play with instead of of a Wii or Nintendo

I know once again, i will make 'friends' and e-mail breeze with this comment...

[Tobias]

Here is what I have and it seems to work great in the simulation software. I am now bench testing and have a few questions. I can add voltage into the circuit on the bench yet it seems very noisy. For example Pot1 is outputting average 1.33v with a VPP of 240mv. The output of Op-Amp1 is average 1.48v with a VPP of 1.12v.

I am using an AD5220 10k digital pot and a L272M Op-Amp. Here is a link to the basic info regarding the Op-Amp.

http://search.digikey.com/scripts/Dk...=497-1387-5-ND

This is my first attempt using Op-Amps. There seems to be a hell of alot of variations to choose from. What would cause the noise? If I am off on the correct Op-Amp, please suggest a replacement. Thanks