AVR-Chat

----- Original Message -----
From: "Wagner Lipnharski" <wagner@ustr.net>
To: <AVR-Chat@yahoogroups.com>
Sent: Thursday, April 08, 2004 14:31
Subject: Re: [AVR-Chat] current in MCU and thte sleep mode
at mega16 issue


> erikc wrote:
> > ----- Original Message -----
> > From: "jay marante" <jaythesis@yahoo.com>
> > To: <AVR-Chat@yahoogroups.com>
> > Sent: Wednesday, April 07, 2004 04:29
> > Subject: Re: [AVR-Chat] current in MCU and thte sleep
mode
> > at mega16 issue
> >
> >
> >> any suggested DC-DC converter? i prefer from texas
> > intruments or maxim. they're the only company i can ask
for
> > samples. it should be five volts output.
> >>
> >> thanks for the help.
> >>
> >> -jay
>
>
> If you are using only an AVR with LCD and keyboard, I
guess you don't need
> to have exactly 5V for supply. The AVR stands lower
voltages and also the
> LCD.  Try to find out what is the minimum voltage you
should supply for the
> LCD to work properly. I guess anything above 4.2V will be
ok.  Reducing VCC
> will also reduce AVR current consumption, what extends
battery life.

Reducing the clock frequency also helps since current
consumption is proportional to clock frequency.

> There is a little trick to use LCD and AVR to reduce
current consumption.
>
> It involves to supply the LCD with the minimum possible
voltage, lets say
> 4.2V, then supply the AVR with the same 4.2V but with a
series diode to its
> vcc pin, capacitor to ground.  It reduces VCC to AVR to
around 3.6V.
> If the AVR stands that low voltage, it will run fine and
the logic up level
> of AVR, around 3.6V, will be considered "up" level by the
LCD, so no
> problem.
>
> The main idea is that AVR reduces current consumption with
low VCC, so,
> inserting the diode in series, will also reduce its
overall current
> consumption.

The LCD displays I'm familiar with all need between 4.5 and
5.5 volts to operate correctly.  They also consume very
little current since they run so slowly.  (I think thier
internal clock is something like 200 KHZ or so.)  You can't
reduce the AVR's Vcc below half of the display's Vcc
otherwise the display will not recognise logic high levels
coming from the AVR.  Maybe two or three diodes in series
should be sufficient.

Then going with the switcher's I mentioned earlier, you not
only get more efficient power transfer to the load, but you
can drain the battery to exhaustion as well.


Erikc  - firewevr@airmail.net
///
"An Fhirinne in aghaidh an tSaoil."
"The Truth against the World."
        -- Bardic Motto