> He also suggested, "A good start might be to explain the 
> sub-circuit of R2, D3, C2, and Q1 near the center of page 1.  
> What does it do?  Why is it needed?  Explain its detailed 
> operation.  What does each part do?"
> 
> Ok.  Here goes.
> 
> Working left to right, a clue I got from Olin, the first 
> thing I see is a USB port.

Olin suggested to concentrate on R2..Q1. Those components are a pattern
that you might understand, or even recognise. Don't attempt to start
with something that is way over your head: you will fail and get a bad
taste from it.

> L1, the choke or coil, will smooth out DC current.  It's 
> either there because it is a good idea, or Olin knows that 
> USB power isn't steady.  Or it is there for another reason.

It is part of a step-up switcher. You won't understand that pattern
without some basic knowledge of how a coil (induction) works. 'it
smooths current' is almost good enough, but only if you take that to its
logical extreme.

> There is a PIC10F204, IC2.  According to the datasheet this 
> PIC has, among other things, I I/O pins, 1 comparator, timer 
> and WDT, max speed 4MHz, and ICSP (in circuit debugging support).

ICSP != ICD

> I don't find any answers to this in any of the books I have 
> (not that they aren't there.) So D1 and SH1 have me stumped.

I would advise you not to start with a circuit and then try to find
parts of it in the books, but the other way round: start with the books.
That might be a less 'nice' route, but there is no royal path to
mathematics, and none to electronics either. (There is none to real
in-depth programming either, but in programming you can get a long way
with only superficial knowledge and a lot of improvising.)

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: www.voti.nl/hvu
 

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