Homebrew PCBs

On Friday 08 July 2005 02:27 pm, Greg Codori wrote:
> I've found quite a few NPN parts, but most of them are substituting a
> 400v part for a 100v part...pretty broad range for a replacement part.

I wouldn't go up there unless I had to.  As you go to higher collector 
breakdown voltage ratings you sacrifice either gain, frequency response, or 
both.  And I have a fair amount of that stuff kicking around,  mostly 
salavaged horizontal output devices.

> > I show that as being an NPN Silicon transistor with a Vce of 45V,
> > an Ic(max) of 800mA,  a power rating of 625mW,  and a beta range of
> > 160-400
>
> (((SNIP)))
>
> > > http://www.vishay.com/docs/88501/1500z.pdf
> > > b40c1500r - 1.5a bridge rectifier
> > > elfa#70-050-93
> > > $1.08 EU
>
> ((SNIP))>
>
> > See above.  And feel free to point me at a schematic someplace (if
> > it's online) or shoot me a copy in email (if it's not) and we'll take it
> > from there.
>
> Here is the schematic
> http://home.no.net/paolsen/mj/dnl/Schematic.pdf
>
> here is the partlist
> http://home.no.net/paolsen/mj/slncmst_p10.html
>
> Parts BR1 and Q1.

Ok.  As far as the bridge rectifier goes,  I'd worry about form factor when I 
was doing repairs,  otherwise just use whatever you can find that'll meet or 
exceed those ratings.  I did a lot of "1541" disk drives (for the c64) and 
they used 1A (!) bridges in there which would succumb to the heat after a 
while.  I found an identically-packaged unit at Radio Shack rated at 4A that 
fit right into the same holes,  an all-pins-in-line configuration.  Also 
salvaged a 4A bridge out of a printer board in the past couple of days that 
happened to be rated at 4A,  so it's whatever's convenient and cheap for you.  
And there's plenty of stuff out there.

For the transistor I can see where they're switching low-level signals (from 
the use of the +5 supply) though I'm not sure at what rate they're going 
since that whole thing is fed from the output pin of that PIC or whatever it 
is.  *Real* non-critical,  and just about any NPN transistor will work in 
there,  as well as darn near any PNP transistor for Q2 -- I'd use 2N3904 and 
2N3906 for those if I was building this.

> This schematic is a control station with a built in power supply.
> This control station generates electronic pulses through model RR
> tracks which are decoded by chips within individual locomotives
> (model RR has an electronics part of the hobby, by the way).

Yeah,  I'd like to get more info on that stuff.  Are you familiar with Rob 
Paisley's pages?  He has a whole mess of good info out there.  Please feel 
free to pass along any links that you might have to other useful electronics 
stuff in this context.

> I'm trying to rebuild the schematic into a board design through
> Eagle.  There are PDF files of the board as designed, but I can't
> convert PDF files into eagle files.

One of these days I'm going to figure out some way to get info out of PDF 
files,  other than by printing the damn things out and then scanning them 
into some other format...

> They are located at
> http://home.no.net/paolsen/mj/dnl/SLNCMST11_layout.zip
>
> Anyone know how to convert pdf's into eagle board files?

The trouble with trying to get info into Eagle or any other schematic capture 
program is that you have an image,  and the program wants to deal with a set 
of objects with defined relationships,  which is not at all the same thing.  
I guess we need something like OCR for images,  or at least for schematics,  
and I'm not the person to write _that_ program!  :-)