Hi Craig,
> I'd like to use the GPIO lines of the processor, and have
> read the warnings about applying 5V logic levels to 3.3V
> logic levels. Sounds dangerous :)
>
> I need both to drive 5V TTL devices as well as get input
> from 5V TTL devices. I've been reading a little, and was
> curious what you all thought.
In addition to being concerned about the voltages, you
also need to consider whether you will ever power-off
your board, while the 5V inputs are still active.
Fairchild and TI have many parts that'll work. I'll often
use TinyLogic parts from Fairchild as I can scatter the
bits around where ever I need them (makes layout dead easy),
and they're tolerant to voltages up to 6V.
Soldering SMT devices is really very easy. You use a flux
pen to wet the area to solder, solder the part down,
making as big a mess of the job as you like, and then use
a flux pen to wet solder wick and use that to remove the
excess solder from the pins. Then spray flux cleaner and
use a kimwhipe ('chem-whipe' kind of like a tissue but not
as fragile) to get rid of the excess flux around the area
you were soldering, and viola, it looks like you made a
perfect soldering job.
> What I found was a Texas Instruments IC, SN74LVC4245A
> OCTAL BUS TRANSCEIVER AND 3.3-V TO 5-V SHIFTER
> (http://www.ti.com/lit/gpn/SN74LVC4245A) which seems
> to do the job. Unfortunately, it's a 24 pin surface
> mount, and I don't have access to high end breadboarding
> equipment for surface mount devices. A DIP does not
> seem to be available. Low end breadboarding solutions
> like the surfboard (http://www.capitaladvanced.com/products.htm)
> seem to only go up to 20 pins.
>
> Questions:
> 1. What are people using to convert 5V TTL to 3.3V and vice versa?
> 2. Does anyone have a relatively inexpensive solution for breadboarding
> surface mount components?
There are soldermount adhesive boards that can handle
these devices. Looking on the packaging I have it has
Wainwright written on them, Google shows up RDI/Wainwright,
but the web site is dead. Perhaps you can find them.
I suspect there was just not a big enough market for
the parts.
Even knowing about solder-mount pads, I would generally
not use them anymore. I find it much simpler to layout
a simple PCB with headers, and whatever power-sources
I decide to put on it.
Check out http://www.barebonespcb.com
They're a 2-layer board company that is part of
Advanced Circuits. You layout your board, upload it
to www.freedfm.com (Advanced Circuits design checking site),
and then upload the 2-layer board files to Barebones.
There is free PCB software on Advanced Circuits web site,
and there is the free KiCAD software that looks to be
pretty nice too.
Cheers,
Dave
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