Experience. You should check the datasheets, even though it is time-consuming. After a couple times, you'll know it for the next time around. When laying out a board, I almost always have Digikey's and Mouser's web pages open so that I can check parts quickly for their datasheets and availability. For 1/4W resistors, I generally mount them vertically, and use the "RCL" --> "R-US_" --> "R-US_0204/2V" component. For 1/2W resistors, the same part works, because the lead diameter is the same. But when I want to mount a 1/2W or 1W resistor horizontally, I will check the datasheet. I've run into problems in the past where a component's leads would not fit into a hole when I just chose a generic library part. In some cases I created my own library part, even for passives. This way I know I have the correct package size, pads, and I get away from those oval pads that they like to use for many components. Cheers, -Neil. On Thursday 01 September 2005 12:24 pm, G Minch scribbled: > Hi, > > I recently started using Eagle to lay out PCBs. Most of the issues I've run > into are typical of learning any new program and generally are resolved via > RTFM. There is one problem that doesn't look like it will go away: generic > devices in the library are specified by package type. > > So, I want to put a 1/2 watt carbon resistor on my board. Great. What > package is that? I haven't a clue. What if I want a 1/4 W metal film > resistor? Same problem. This reduces me to a trial-and-error approach to > picking the correct package size. > > Some component packages, such as those for transistors and diodes, are > pretty easy to find & I already know most of the common sizes. But when it > comes to things like resistors and capacitors it is difficult to find > package information except through manufacturer data sheets; a > time-consuming process. > > What I'd like to do is whip out my Instrument of Measurement (commonly > known as a "ruler") and eyeball the component, then consult a chart and > pick the closest package size. > > My question is this: Where can I find a general reference for package > designations and sizes (US units) for passive components? Preferably, > something free and on the 'net. > > Thanks in advance for any info. > > Glenn Minch -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist