[Arm-netbook] Use of 2N3904

[jm]

On Sat, 2012-11-10 at 12:03 +0000, luke.leighton wrote:
> On Sat, Nov 10, 2012 at 11:39 AM, jm <joem at martindale-electric.co.uk> wrote:
> > On Fri, 2012-11-09 at 20:49 +0000, luke.leighton wrote:
> >> On Thu, Nov 8, 2012 at 11:08 PM, jm <joem at martindale-electric.co.uk> wrote:
> >> > Hi,
> >> >
> >> > I'm helping out with design checking
> >> > http://rhombus-tech.net/community_ideas/kde_tablet/news/
> >> >
> >> > Can anyone tell me the price advantage of 2N3904 over a 2N7002 (Far East
> >> > pricing).
> >> >
> >> > The changes as example to section with Q3:
> >> > 1. replace 2N3904 with 2N7002
> >> > 2. remove C160
> >> > 3. remove R58
> >> > 4. Change R56 to 100K
> >> > 5. Change R61 to 10K
> >>
> >>  ahh, you're a star.  ok i take it that's for the NRESET transistor as well?
> >
> > Yes it does for NRESET.
> > If the lines are rarely used (as is normal for reset signals),
> > then they can be 33k with no adverse effects.
> 
>  ack.  err... which ones - both of the resistors?

My bad - R61/R68 change to 33K

> 
> >> > would make the circuit work equivalently and less prone
> >> > to effects of touching and hand grease finding itself
> >> > on the PCB and adversely affecting circuit.
> >>
> >>  superb.  thanks joe.  wouldn't occur to me, that :)
> >>
> >>  ... would you be willing to look at the audio (transconductance amp)
> >> and the mosfet h-bridge one as well?
> >
> > To be quick with circuit + PCB analysis, the following can help you and
> > me:
> 
>  ack! that works for me
> 
> > 1. Leave links to datasheets to important chips below diagram.
> 
>  oo that's a good idea - i wondered how to do that!  i could put it as
> a field into the database of parts, then, hmmm, that goes into the BOM
> if you ask it to... yeah, i'll do that.
> 
> >    Keep those datasheets in one directory so that once that
> >    place is found, we can find all the related datasheets quickly.
> >    STM32F103 for example. The inductor. S6M1, LM13700, RT8020,
> > LC5730,etc etc
> >
> > 2. When drawing circuits, draw them as you might find them in a text
> > book. When orientations and positions of components change, its hard
> > work locating mistakes quickly.
> 
>  i started out doing cut/paste of app notes and other peoples'
> circuits.  am veeery slowly progressing in a random direction beyond
> that point :)
> 
> > 3. In complex systems like computer boards, use drawings of chips that
> > most resemble physical pin layout. It helps plan final layout, and with
> > debugging.
> 
>  ahh, ok.  right.  oh well.  i changed the STM32F one to be a split
> part because i found an eagle jobbie with that, but yeah i get it.
> 
> > U34 for example is prone to pick up so its good to know where
> > to place the mic in components and you may as plan from the schematic by
> > drawing the shape of U34 and its pins accurately.
> 
>  ah.... i think...  you mean the .... unf?  
> where's U34?  oh

Another idea - name all diagrams figure1, Figure 2, etc.
Helps with group working.

> rightright, ok, yes i'd deleted one of those, so yes, the LM17000 -
> yes, that came from allegro's own database, yes it's a bit shit
> layout: parts that i've created (except the STM32F where i did
> actually originally copy the pinouts oh well) have followed that
> rule.. mostly :)
> 
> > Its very important
> > that all the chips and numerous wires and positions of components are
> > subtly planned from schematic so there is less work in the final PCB
> > layout. Another example, the inductors for U28 pins 2 and 8 can't sit
> > next to each other in case they
> > interfere with each other. Knowing the pin positions accurately
> > to the real chip would allow us to plan where the inductor is positioned
> > in the schematic to hint at where it should be in the final layout of
> > PCB.
> 
>  ok sah.

What I do is gather up all your schematics, and make a duplicate
in KiCAD into one big drawing. That way anyone can download
KiCAD for free can also join in and make submissions.

:-)

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