Harold, And in addition to this regarding the PC board traces and currents, wheneve= r you have a high potential Running through a trace on a PC board, and the trace has to make a directio= n change, make sure you use A gentle radius to make the turn and not a sharp 90 degree turn, because th= e sharp point resulting from = the turn is a high stress point. That's where all the electrons gather whi= ch build up a high potential, basically from a point source, which can disc= harge to anything close by that is of lower potential. When you use a radiused corner, the sharp point is gone and there is no hig= h stress point. Or at least not To the degree that there is with a sharp 90 degree turn. Just an FYI. Jim = -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of= Ruben J=F6nsson Sent: Thursday, November 06, 2008 4:14 PM To: Microcontroller discussion list - Public. Subject: Re: [OT] How should I teach electronics? > various components. On op amps, I use the "theory of the happy op amp" > that assumes the two input voltages are the same. Determine the = > voltage at the non-inverting input, assume the inverting input is the = > same, and analyze from there. > = > Good luck! > = > Harold > = The eye opener with op amps for me was when I realized that as long as the = positive input is at a higher voltage than the negative, the output wants t= o go high (all the way to the rail if it can) and the output wants to go lo= w if the positive input is at a lower voltage than the negative. If the inp= uts are connected correctly, the feedback network won't allow this to happe= n since the voltage on one of the inputs (or perhaps both) is affected by t= he op amps output making the output stabilaze at the voltage that results i= n both inputs having the same voltage. From here on it is simply ohms law t= o calculate the DC gain and the output voltage given the input voltage. Another eye opener in visualizing EMC and emitted radiation on a circuit bo= ard is that all electrons pushed out (or sucked in) by a power supply or dr= iver through a circuit needs to have exactly the same amount of electrons r= eturn to it. Keeping these current loops as small as possible won't let the= currents wander around all over the circuit board, possibly by capacitive = coupling, creating fields and voltage drops. If the current needs to travel= a long way, make sure that the return current can run close to the output = current to even out the fields created by them. Thinking like this also hel= ps visualize current paths in high voltage applications (like 10kV or more)= where electrons are sucked in or pushed out of emitters in order to create= air ions. An electron can only leave the circuit if another one can be bro= ught in, hopefully through a dedicated, low ohm earth connection and hopefu= lly not through capacitive coupling against an earth plane or other conduct= or. Capacitive coupling goes a long way with high voltages. /Ruben =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D Ruben J=F6nsson AB Liros Electronic Box 9124, 200 39 Malm=F6, Sweden TEL INT +46 40142078 FAX INT +46 40947388 ruben@pp.sbbs.se =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membershi= p options at http://mailman.mit.edu/mailman/listinfo/piclist -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist