Re: [avr-chat] AVR board with USB and LCD

[Marvin Dickens]

On Thursday 02 June 2005 03:43 pm, Pertti Kellomäki wrote:
> 2. kesä 2005 kello 00:27, Gary Douglas wrote:
> >  If you wanted to do a board yourself - or modify your STK500 or
> > similar, you can check out serial interface displays from Matrix
> > Orbital http://www.matrixorbital.com and USB Uarts from FTDI (
> > www.ftdichip.com ) - these might save you a lot of time!  I've used
> > the latter with great success!
>
> I am more of a software guy, so I am trying to get by
> with modules that I can buy. I ordered a couple of
> DLP-USB245M modules with FTDI chips, which seem
> to be pretty nice. One thing I am a bit confused about
> the chip is whether it is possible to produce a purely
> 3.3V design. There is an example of a bus powered
> 5V system with 3.3V interface in the module's User
> Manual, but it does not show where the 3.3V power
> supply for the microcontroller comes from. Could I just
> substitute a Butterfly with its lithium battery for the
> microcontroller?

You need to make sure all of your peripherals are the same voltage because
it is very likely that most of the modules that you purchase are going to
be 5 volt (It's the way many modules come). It is possible to have 5v and 3.3v 
in your design, but it adds complexity to the design you may not want to deal 
with. If you have 3.3v and 5v power in the same design, get 5v power from
one regulated source and 3.3v power from another regulated source. I advise 
against trying to step down 5v power to get 3.3v power.

You can find 3.3v modules if you look around, but they are going to cost more 
$. Also, in the event you are going to use batteries, you need add up the the 
total power consumed by all of your peripherals plus the mcu and make sure 
your design is not under powered for your intended application.

Regards

Marvin Dickens
Alpharetta, Georgia

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