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Re: gEDA-user: OFF: triac
DJ Delorie wrote:
DJ - If you redo the pcb - please consider reworking the physical layout
so all the mains stuff is physically separated from the logic-level
stuff that people might come into contact with. A mains wire breaking /
falling out of the screw terminal and touching control wiring can have
interesting consequences.
It's only a 24vac system on the "mains" side, not 120vac. Well below
the ouch threshold. These are the same wires that are normally strung
throughout the house, hooked to flimsy thermostats and such.
I missed that point. The current standard is fine for 24V :)
But on the new one, the terminal blocks are all along the edge, with
the circuitry behind them and the wires on the "outside". This is the
layout so far (no schematics yet, just fiddling with component sizes):
http://www.delorie.com/house/furnace/furnace2.png
The green line is the 6mm gap between the 24vac side and the 5vdc
side. All 5v-side connections will have multiple ESD blocks on them.
When I get to that point, I'll probably start posting schematics as I
develop each module, for feedback and insight.
Thats certainly a lot cleaner than the existing. I'm not sure what the
polarized things at the top are - but you could consider bringing then
closer to the centre of the board, and running all 'mains' down one long
edge. Might be even better.
I've talked with Digikey and they expect to get some new top-access
terminal blocks (weidmuller LSF-SMT 3.5mm vertical) by mid-year. That
will let me put them closer to the edge and reclaim more board space
for logic. I'm hoping the straight-in connection will reduce the
number of stray touches during setup, not that I put any traces on
those parts of the board.
perhaps also consider 5.08 pitch pcb sockets and matching line plugs,
Farnell has then as say 3705174 , 3705535, 3705262.
(sending a farnell search link is a bit long)
I'm sure other places local to you will have them at real prices.
Being able to unplug the wires is nice for working on things.
Blocks of 2--4 pins seem to be good.
I used to use board mounted screw terminals, I've moved over to plugs
for all recent stuff. The extra couple of dollars is well worth the
convenience.
I'm also thinking this should be a 4 layer board. The extra ground
and power planes will also help protect against ESD and inducted
spikes both by providing the capacitive planes and avoiding
antenna-like ground paths, and lets me hide the AC "mains" inside the
board.
If you get hit by lightning lots of ESD protection won't help much. ESD
protection does help against a nearby strike. Make sure you provide an
easier path to ground - which has to be complemented by a good
high-current ground path that is _not_ back through your PC.
I added a nice big ground wire to a metal water pipe after losing a lot
of stuff a couple of years back.
And the alternistors have isolated tabs too.
make heatsink and don't touch labels both easier :)