On Sat, Apr 5, 2014 at 4:28 AM, Kerusey Karyu <[email protected]> wrote:
> W dniu 03.04.2014 02:24, Carl Poirier pisze: > > > About pin length, what about using SI units? >> >> At this point, we shall to ask: How many users use SI units when drawing > schematics? Most of them will look at grid only and doesn't care about mm > or inches. > Units of measurement are important, but where they are actually required > to maintain strict dimensions. > If you look at the metrication of the world, you will notice people using the imperial system are getting scarce these days. http://en.wikipedia.org/wiki/File:SI-metrication-world.png > > > Symbols: >> >> 1. A pin length of 4mm is used, except for components without pin >> numbers which use 2.5mm. >> > > > If we force 4mm or 2.5mm of pin length these pins will be outside of the > grid when somebody uses inches. IMO this is not the way we should follow. > > Same can be said when one uses the SI system to draw his schematic. > > > Footprints: > > (...) > > 2. Pad 1 is placed at the top left corner >> > > > (...) unless the manufacturer places the components in a different > orientation in tubes, tapes or trays (Important for P&P). Good point. Can you tell me, for a device that's made by many manufacturers and sold in such packages, do they all use the same orientation? > 3. For through-hole components, origin is set on pad 1. >> > > 4. For surface-mount devices, origin is placed in the middle of > > the chip. > > > There are also machines for automatic insertion of THT components, so > mandatory putting origin point at pad 1 is a bad idea. > We can assume to put origin at pin 1 when we are sure that this component > will be inserted manually, for example terminal blocks. > > Jean-Paul Louis was telling me that "By convention, the through hole IC were referenced to the pin one because of the insertion machines." So this isn't always the case?
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