Lpc2000

Just throwing out some additional ideas, as I am in the same boat you are 
(just starting out here):

For the +5v (is this really needed?)  You can try something akin to what 
you can do for a simple RS232 level driver:

http://www.piclist.com/techref/io/serial/ttl-rs232.htm

Basically using some resistors, diodes and caps you can steal power from 
individual lines, gang them together if needed.  You'll need diodes with 
really low level drops however to make this effective.

Alternatively you could try a simple voltage doubler circuit with a pair of 
normal-drop diodes.  3.3 * 2 = 6.6 - 2*0.7 = 5.2V which should work pretty 
well for the current levels required.

The wall brick really isn't necessary, and will be expensive and 
cumbersome.  You could always use something like MAX682/3/4 charge pumps 
(still cheaper than wall brick, or get a few samples for free), or 
alternately something like the
LM4871 audio amp can give a simple 3.3V to 5V conversion:

http://www.edn.com/article/CA240909.html

Or possibly a NJU7261U50 switching regulator (about $1 plus only a few 
external components) for 3.3V to 5V step-up at 250mA.

You may want to take a look at the 74LVC4245A part (CMOS OCTAL BUS 
TRANSCEIVER AND 3.3V TO 5V SHIFTER; but without schmitt), instead of the 
inverters.

As well since there are additional IO pins on the LPT side unused, is there 
anything we can do with this?

Perhaps add in an LED or two to give a visual indication of what is going on?

As well instead of using a 74HC14, how about 74AC08 quad AND-gate?  You can 
drive higher current, and you only need 4 gates anyway.  You won't get your 
5V side logic or schmitt either though (again, is this necessary?)

I know of several places of getting PCBs made fairly cheap, so if we can 
work out something that works well I wouldn't find footing some cash to 
have a pile of PCBs made to sell to the DIY-ers out there.

-- Sean

At 11:54 PM 1/16/2006, you wrote:
>Thank you for all the suggestions. I have put together an initial
>schematic diagram using 74VHC14 schmitt trigger inverters and RC low
>pass filters (as suggested here):
>
><http://www.k9spud.com/jtag/>http://www.k9spud.com/jtag/
>
>I'm not sure how to add additional signals like RTCK and nTRST. Won't
>these kind of changes require software support on the PC to be useful?
>My understanding was that the Macraigor software was not open source.
>Where should these signals be connected to on the PC side?
>
>Or are you just suggesting a jumper for the user to manually switch by
>hand?
>
>What is the nTRST signal useful for? I'm new to JTAG, just trying to
>get my first ARM project started.
>
>--- In lpc2000@yahoogroups.com, "Arie de Muynck" <mygroups@x...> wrote:
> >
> > From: "Bertrik Sikken" <bertrik@z...>
> > > Perhaps we can improve upon the existing designs and create
> > > the ultimate low-cost ARM JTAG cable, yet keeping it simple.
> > > Some ideas:
> > > * provide proper current limiting for all lines
> > > * add readback of the RTCK signal (return clock)
> > > * add readback of the targets' VCC (like the Olimex clone does)
> >
> > Also:
> >
> > * use proper level shifting buffers or separate buffers for the LPT port
> >   side(5V logic) and the target side (target voltage).
> > * use low-pass filters (RC) + schmidttrigger receivers on the LPT
>port side.
> > * series termination resistor on each driven line, to LPT and to target.
> > * a (jumper selectable) nTRST drive, separate from the nRESET drive.
> > * optional: a 1mA LED indicator on the target side VCC.
> >
> > The problems occur not just with building the thing - it's the wiggler
> > design itself that is a bit flakey, especially the lack of a noise
>filter
> > and schmidttrigger receiver on the CLK input at the LPT side. A
>100...400
> > nsec RC filter should do it while still allowing up to 1 MHz
>clocking (above
> > LPT port speed levels). If this is not present, long LPT cables or
>improper
> > grounding will cause glitches that upset the JTAG state machine.
> >
> > I fail to see the actual use of the RTCK signal - is this to be
>tested by SW
> > on the LPT status bits? Which CPU is so slow that this would make a
> > difference?
>
>
>
>
>
>
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