DIY Stompboxes => Digital & DSP => Topic started by: zerohero on May 25, 2007, 05:13:05 PM

Title: A little confusion
Post by: zerohero on May 25, 2007, 05:13:05 PM
Hey, I am a bit confused over the analog and digital ground business. ive done some digital logic stuff and plenty of analog but untill now havent tried to fuse them together. I am also attempting to build an effects switcher and i was drawing up my schematics realizing that i was not personaly confident with the concept of the different analog and digital grounds.

So on the MT8816 you have VSS (digital ground) VEE (negative supply) and VDD (positive supply). and my understanding is that the logic 1's and zero's are between the VSS and VDD. so my confusiion comes with two things. 1: if i am having audio signals connected directly to the chip i am asuming that i would bias them at VSS so that the signal has the most headroom peak-to-peak. is this wrong? and 2: if my mcu is going from ground to 5.5 V how to i connect the two so that the logic will match? sorry if these are obvious questions i searched but all i got was mention of the concept and not an explanation.

thanks as always

Title: Re: A little confusion
Post by: Chuck on May 26, 2007, 05:11:14 PM
There's no way I could exxplain this as R.G. has in previous posts here.  Look in the Project CrossBar thread.

But I supply 5 volts to the MT8816.  Thats VDD.  I put the power supply ground, thats digital ground to VSS.
VEE is the reference ground.  There I use -5 volts.

R.G does it a little differently, but I can't "hear" any problems with my method.

I get the negative -5 volts by using a charge pump circuit with a MAX1044 charge pump.  Its actually very easy to use.