AVR-Chat

--- In AVR-Chat@yahoogroups.com, David VanHorn <dvanhorn@c...> wrote:
> At 09:16 AM 7/30/2004, C Sizer wrote:
> 
> >Hi guys,
> >
> >I am designing a university project, a hand-held printer using the 
> >AVR and a small thermal printer. For portability I want to use 4 x 
> >2300mAh AA batteries in serial/parallel to provide me with 3V.
> 
> Shuttle or line mech?  Line is much faster, and much more demanding.
> You need roughly the same horsepower as a laser printer of the same 
size would.
> 
> >The printer runs on 5V but consumes over 3.5A peak, so I require a 
DC-
> >DC converter circuit (or at least a starting point) to provide 3V 
at 
> >5A peak.
> >
> >Has anyone designed anything like this, or can give me some 
advice? 
> >Maybe someone has an idea for a better battery for me to use?
> 
> You'd be far better off to put your batteries in series, and then 
buck regulate the 3V.
> There are pulse-skipping converters that are very efficient. If the 
current is low enough, you can win with analog again..  Then again, 
why not run on 5V?
> 
> Also, do the math on burn energy, you'll find that the faster you 
print, the less energy you spend.  A significant amount of your print 
energy goes into heating up the printhead mass.  Wake up, go like 
hell, shut down.
> 
> Dedicate a timer to the stepper, and another to the burn.
> Use the burn timer like an alarm clock, interrupting you when the 
first head group is done, then reload for the remainder of the burn 
on the second group, etc.
> 
> You can start the burn pulse with a nominal value, do the 
calculations (FMULT is your friend) and then change the timer setting 
to the calculated burn width.
> 
> The stepper will need to be accelerated, and decelerated, depending 
on how much rasterized data you have built up. 
> 
> The SPI port is great at blowing out data to the head at high 
speed. 
> 
> I did one early this year, using a Mega-8 with on-chip osc, and a 
stepper driver IC.
> It was capable of running the mech at full speed, which ended up to 
be faster than the 1.7 GHz laptop could send the data out.

> 
> You'll find the details of getting this going properly, quite 
interesting.

Hi David,

thanks for the input.

I did make a mistake in my email, I want the output of the converter 
to be 5V not 3V.

The printer is an OEM module complete with controller etc. I am only 
interfacing it to the Atmel via RS232. The time I have to develop 
this project would not allow me to go to the lengths you describe 
here, although as you say it would be an interesting exercise. The 
printer can be configured for optimal speed/power, I am not 
interested in speed but low power consumption for my design is to be 
hand held. The printer is a line thermal using 60mm wide paper.

My concerns are size, weight and power consumption. If you know of 
any more suitable battery/powersupply combinations I would be 
greatful for your input.

Cheers
Col