Meese, did the needle cord and needles get to you?
Yep just got it, Thanks again! I'll try it out in a little after I scrounge around for a BNC jack in my random parts bin, know I had one somewhere... or change to a 3.5mm connector failing that.
(Seems like a LOT of electronics just for a simple DC circuit. I made one with a 9V battery, a "pot" and a DC meter. And, of course, a positive wire and needle cord.)
See 2 posts above for the exact what the additional circuitry does. It's not really a necessary addition but it still does help . Making little electronics/software projects like this is fun for me and the engineer in me has a compulsive need to make things better.
Also whatever blend machine you use would very likely have something similar, if its something like DC strength 1-100 then using 50 will probably always give you 500ma no matter which person it's used on (though they probably used some sort of digital potentiometer/DAC that outputs 12v by itself and doesn't need the additional opamp I had to use since my 5v DAC was just what I had lying around).