Re: [avr-chat] battery-operated AVRs

[David Kelly]

On Tue, Mar 11, 2008 at 03:36:38PM -0500, Marge Coahran wrote:
> The circuit load is small. I want to drive a 7-segment display with one 
> AVR, and a piezoelectric speaker with another.

When you say "small" and "7-segment display" in the same sentence I
think your definition of small and mine are not the same.

You will need 5 mA to 10 mA per segment to drive an LED display, while
your entire AVR will be drawing about 1 mA per MHZ.

> I had not been using a bypass capacitor, so I have added one.

Is important but shouldn't be a show stopper, especially when powering
off battery.

> Perhaps my misunderstanding is about the AVR. I have programmed the
> chip, and I thought that simply giving it power would cause execution
> to start.  Is this correct? Do I also need to pull reset low to start
> execution?

The ATmega parts I have used worked without external reset altho I put
10k or 47k pullup on the reset pin. This is where one needs to read the
data sheet for oneself. There is probably an internal pullup on your
reset pin. Put a voltmeter on it and see what is happening. Try shorting
it to ground and see if things start.

Measure VCC at the chip to see if its what you expected. If VCC is
reasonable at the chip then your supply is not being overtaxed.

Your 8515 doesn't run under JTAG ICE or DebugWire? If that is the case
then you should change CPUs to one that does. There is no point in
suffering without in-circuit debugging in this day and age.

-- 
David Kelly N4HHE, address@hidden
========================================================================
Whom computers would destroy, they must first drive mad.