Date : Tue, 13 Sep 2005 09:12:19 +0200
From : John Kortink <kortink@...>
Subject: Re: 101 uses for a speech system (number 47)
On 12 Sep 2005 23:53:11 +0100, Jonathan Graham Harston wrote:
>> Message-ID: <4da920f69ainfo@...>
>
>Sprow <info@...> wrote:
>
>> As I was doing the layout for JGH, his requests get higher priority.
I'd
>> have probably gone for a programmable logic device and all surface
mount,
>> but that's just me, and means it's no longer made from off-the-shelf
parts.
>
>I specifically wanted not to use a programmable logic device,
>because it means that you have to have a programmable logic device
>programmer before you can even consider thinking about building
>the interface.
You just need the pre-programmed chip. Much like you
can't make your own TTL ICs, and a 74HCT646 or BAT54A
can not always be readily obtained in any electronics
store on the corner the only issue is where to obtain
it, not how. A matter of distribution, not production.
>I wanted a design that anybody could build with
>just a soldering iron, regardless of whether I had fallen under a
>bus and taken cruicial parts of the design with me.
You can easily give that design to others, and they'll
be able to reproduce it. Programming a finished design
into a PLD is not exactly expensive or complicated. You
need the source (or object) file, a PC with a parallel
port, a programming cable (5 UKP in parts if need be,
circuitry usually freely available), and downloadable
software from the chip manufacturer.
It's basically just as 'complicated' as giving someone
source code and arranging a way to recompile.
The only difference is the design is not easy to adapt
without first learning about logic programming. But
then again the man in the street won't know how to
adapt circuitry containing a handful of TTL chips
either.
>Every design but one that I found on the Internet for various IDE
>interfaces were built around a PLD, and were consequently utterly
>unconstructable because there was no way somebody could walk into
>Bardwell's, Farnel's or Maplin's and get the cruicial part that
>these designs put almost the entirety of their design into.
No, but it's easy to arrange for them to only need to
'walk' a little farther. See above.
>Particulalry annoying when the design essentially boils down to a
>small handful of gates that fit into 80p's worth of ICs.
A PLD will turn out to be cheaper, I can assure you.
PCB space, sockets, ... 80p is a little optimistic
as well ...
>I specifically wanted non-surface mount components so that anybody
>who was comptent with a soldering iron could build it, not PCB
>construction freaks with specialist surface-mount construction
>equipment. If I had enough money for surface mount equipment, I'd
>spend it on computer equipment, or food, or the motgage, not SMT
>tools.
No specialist tools are necessary to solder most
regular SMT parts.
I've even been able to solder a large number of
144 pin flat packs (0.5 mm pitch) without it.
Although it does take some skill and practice.
A bigger hurdle is not providing a solder mask.
That IDE PCB was hard to solder without making
shorts.
John Kortink
--
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