Adding voltage to a circuit

[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

[mister_e]

I haven't place your circuit on a breadboard, but i have the following feeling.

Noise can come from each Opamp, and then mixed & doubled with the last stage. Higher your resistor values are, greater the chances to pickup noise... and then you also have the PCB layout, ground loops, PSU filtering etc etc etc.

You want to smooth everything from the port wiper with a capacitor, at the mix point (last stage), and probably at the output of the last one. Some op-amp may react weird with capacitive load so far. RC filter would help, while a bit useless in few cases. Software noise rejection is a common use.

I stick to the idea of a dual rail voltage. This can be easily produced with a simple PWM signal and a capacitive inverter. Match this to a low quiescent current OP-AMP and you're in business.

I have those AD5220 in stock, but not this specific op-amp.. got a load of others though.

I still not 100% understand why you can't trick the whole thing in software instead... i miss the whole idea. Anyways, you know where to reach me