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Re: [avr-chat] New Programmer, Small Program, F_CPU for Atmega644

From: Robert L Cochran
Subject: Re: [avr-chat] New Programmer, Small Program, F_CPU for Atmega644
Date: Sun, 23 Mar 2008 15:27:22 -0400
User-agent: Thunderbird (X11/20080226)

Thanks Marge! I'm glad of the detail because I need to learn and apply
Ohm's law routinely.

This along with Bill saying my first choice of power supply is okay
helps me feel good about going ahead and testing both the circuit and
the programmer. I'll post results later.


Marge Coahran wrote:
> You mentioned before that you intend to blink an LED with this, right?
> You can connect the LED portion of your circuit as either of the
> following, and the resistor can go on either side of the LED. (The
> long leg of your LED should be toward power, or away from ground.)
>   AVR output pin -> LED -> resistor -> ground
>   AVR output pin -> LED -> resistor -> power (VCC)
> You can expect the LED to drop about 1.7V, so if you are supplying 5V,
> you have 3.3V to be dropped by the resistor. Ohm's law (which applies
> to resistors, but not everything) tells us that V = I * R. You want a
> current of about 20mA to light the LED. Thus, use a resistor with
> R = 3.3/.02 = 165 Ohms.  These numbers are rough enough that you
> should be fine with any similar resistor you happen to have.
> Forgive me if this is more detail than you wanted.
> -Marge
> On Sun, 23 Mar 2008, Robert L Cochran wrote:
>> Joerg Wunsch wrote:
>>> Since it's small enough to post, here's the hex file when compiling
>>> for an ATmega644:
>>> :100000000C9438000C9455000C9455000C94550039
>>> :100010000C9455000C9455000C9455000C9455000C
>>> :100020000C9455000C9455000C9455000C945500FC
>>> :100030000C9455000C9455000C9455000C945700EA
>>> :100040000C9455000C9455000C9455000C945500DC
>>> :100050000C9455000C9455000C9455000C945500CC
>>> :100060000C9455000C9455000C9455000C945500BC
>>> :1000700011241FBECFEFD0E1DEBFCDBF11E0A0E065
>>> :10008000B1E0ECE6F1E002C005900D92A030B107BE
>>> :10009000D9F711E0A0E0B1E001C01D92A330B10793
>>> :1000A000E1F70E94AB000C94B5000C9400001F9285
>>> :1000B0000F920FB60F9211242F933F938F9380913D
>>> :1000C0000001882379F420910101309102012F5F12
>>> :1000D0003F4F309302012093010183E02F3F380707
>>> :1000E000D9F417C0813029F020910101309102012B
>>> :1000F00013C0209101013091020121503040309312
>>> :100100000201209301012115310531F41092000103
>>> :1001100003C081E080930001309389002093880020
>>> :100120008F913F912F910F900FBE0F901F901895B8
>>> :1001300083E880938000E1E8F0E080818160808343
>>> :10014000109289001092880080E28AB981E0809341
>>> :100150006F00789408950E94980083B7816083BFF0
>>> :0C016000889583B78E7F83BFF8CFFFCF58
>>> :00000001FF
>> Thanks Joerg for posting this. I have a breadboard circuit ready to test
>> with this hex file. I was planning to use a lithium polymer battery that
>> pumps out 12v at 1300 mA. I connected that to a power supply board which
>> will give me 5v output and 1100 mA current. That is way too much current
>> for the Atmega644, isn't it? The absolute maximum ratings on the
>> datasheet list 200 mA as the maximum on VCC and GND. Of the "wall wart"
>> power supplies I am using, I have one that puts out 5v and I've measured
>> 350 mA current. So I need to cut down the current for the AtMega 644
>> device, right? I can reduce the current with resistors? I will Google to
>> learn how to do this.
>> Thanks
>> Bob Cochran
>> _______________________________________________
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