One of the thigns I've often lamented is the lack of CAD interchange standards and centralized repositories for parts; it woudl seem every single CAD user is doomed to (re)create his own preferred-CAD libraries for both schematic symbols and associated physical parts representation. A huge shame and waste of time, but such is life. I find it a very offputting task .. hey, great, I've got all these ideas, lets throw them down into a schematic and get to pcbdesign……. oh, wait, before I spend 2 hours making the schem and pcb, I need to spend 20 hours collecting parts datasheets, ordered parts to measure with a good caliper, and building the schemtic and part components in the CAD. Oh joy.
Still, has to be done, so best get to it! I've long ago put together components for the various CPUs, and thankfully most CADs (Eagle included) come stocked with some common libraries (capcitors and so forth), so you're not making everything; just all the good bits, or unusual bits. In my case, a fair number of oddball parts.
I've managed to be ill a bit of late, and with March Break had all the kidsw around, so have been out of commission, but hungering to proceed; now that school is starting up and health has improved, I'm trying to get back to the plate for a swing. Real Life Work is really keeping me exhausted though..
.. so in the absence of time for Zikzak work, I've gone ahead and ordered a pile of necessary trinketry from ebay; I need to get on this, to get some parts lined up; all the assorted litlte bits that you don't sweat over when prototyping (any switch will do for on/off, who cares!) but matter significantly when laying out pcb designs (spacing of components, the placement of drill holes and connections, the actual part specs such as wattage and voltage capacity, etc.) So I've placed orders over seas for.. headphone jacks, DC jacks, power posts and banana plug jacks (I'd like to have both a DC jack for a 9V brick, and banana plug jacks for bench power supplies), some toggle switches (for main power) and momentary button switches (for resets and inputs), zener diodes (340 for $6 .. 34 values * 10ea, for prototyping), and some resistor networks (the 7pin guys that offer a stack of 10K resistors all in a catarpiller package, for pull up/downs. Great for those high address lines that most carts will not use…), some LEDs, all that sort of business; thankfully with ebay, these are all rediculously cheap from Thailand or China, but will take 3-8 weeks to arrive. I should've ordered months ago, but … offputting work as I say.
The zeners are just nifty, but I need to read up a touch; I'm getting power spikes from my (crummy) bench power supply when it turns on; I shoudl just fix the supply but I'm not confident in those things yet; a power switch on the board will help (ie: leave the bench on, and power the board on/off using my own switch, means no spike, right?); likewise, using LM7805 for 5V regulator protects that rail, and maybe use L78L33 for 3.3V rail for similar effect (or TI TSP SOIC style regulator chips.) The question is.. if you wrap a zener around the regulator (and not use the zener as a regulator _itself), will it protect from spike.. if you get a momentary 15V spike, and use a 9V zener.. will it shunt off the extra voltage, and keep a clean 9V into the regulator? Something like that.
So, time to prototype out (again) a little power supply, test how safe it is with both 5V and 3.3V and zener going on, and CAD up the edge connector, and some other business, while twiddling thumbs waiting for all the minutia to arrive and get measured…