On 12/23/05, Bill Kuncicky wrote: > OK, guys, thanks for the answers about the electrolytic capacitor. Glad > to know I was right. > > Now, if I am not wearing out my welcome, one more question. A friend > sold me a box full of old capacitors, resistors and TTL chips. He said > that he bought them from some surplus place many years ago, but never > had any need for them since it turned out to be more trouble than it was > worth to go through a whole box looking for some particular value -- he > would rather just go to Radio Shack and buy a new one. But I figure > that I can use them in my lessons. Only problem is, I have heard that a > capacitor will go bad after a certain period of time, and cannot think > of a good way to test one, to see if it has gone bad or changed value. > (A resistor I can check, of course, and a TTL chip I can check). Any > good advice for someone on a low budget? > If you still have your borrowed scope, you can make an RC filter and connect it to an oscillator, then check its -3dB bandwidth against the calculated one. If you don't have an oscillator, a computer with a soundcard will do. (Keep the value of R above 1K or so to avoid loading the soundcard's output.) I guess you could just use the AC-volts range on a DMM. But watching on a scope is better the first time, so you can see what's going on. It's the electrolytics that dry out after a while. But electrolytics usually have very loose specs, and are used in "bigger is better" situations. So small capacitance changes will go unnoticed. Regards, Mark markrages@gmail -- You think that it is a secret, but it never has been one. - fortune cookie -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist