> > This HPS40 is pissing me off.. Half of the rare times when I > can get a semi-reasonable square wave on it, it shows > +/- pulses at the edges. > > Maybe I'll start a new thread about recommendations for > 'scopes.. By +/- pulses do you mean you see ADDITIONAL pulses in the train with positive and negative going directions? Or do you mean combinations of overshoot, undershoot and ringing in the leading and falling edges of the pulse? If you mean the latter, I suggest you study the following from Tektronix. It is among the best application for learning how to use and set up an oscilloscope: http://www.tek.com/Measurement/App_Notes/XYZs/ Translate controls and methods as necessary for your Vellman. Some important points to remember about a scope (even the cheapo Vellman stuff): 1) If using a x10 or x100 probe (x10 is much more common) learn to compensate the probe so that you get the best impedance match and good looking edges. I can't think of any x1 probes I've ever seen that had compensation that worked for a damn if at all. They just have too much capacitance. There are times when 50 Ohm or 500 Ohm direct connect cables and probes are nice and other times when you have to build your own too. 2) If you could have just one probe on your bench, use an x10 probe to minimize the loading of your signal. You can get active probes that have even less capacitive loading and all kinds of special probing jigs and connectors but a nice x10 gets you a long, long way. My personal preference is for fixed x10 probes, not the switchable kind. And many Tek and HP scopes have a little ring and pin setup that can automatically tell the oscilloscope what kind of probe is attached. A very nice feature to look for. 3) Don't use the 6" ground clip for anything except quick probing. It is useless for looking at fast edges. Do this instead: http://www.pericom.com/pdf/applications/AN021.pdf There are other descriptions of the technique out there but the picture in this app note is pretty clear. Its all about the ground loop... 4) Use a probe with at least twice the bandwidth advertised for your oscilloscope. To a first approximation, the risetime of your scope and the rise time of your probe combine as RMS and you will end up with LESS bandwidth than you started with. I think your Vellman is something like 20MHz so a 100MHz bandwidth probe would be OK. But at least read the Tek app note, that answes loads and loads of questions about good scope-ing. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist