AVR-Chat

Hello there


I'm having some weird issues with an Atmega8 based board where the  
processor won't start the program unless the
avrisp dongle is connected.


You can see the circuit here http://www.potemkin.org/uploads/Pid/ 
arduino_rs232_v2.png

the rs232 interface part is not installed.

I've checked and the fuses are programmed correctly (there are about  
1500 usb boards that we sold with the same fuse settings)

it also happened a few times with some usb boards that when they are  
powered via the external power supply they have troubles starting up  
while when powered by the USB they work correctly.


do you have any suggestions?


thanks!

At 10:56 PM 31/03/2006, you wrote:
>an Atmega8 based board where the
>processor won't start the program unless the
>avrisp dongle is connected.

I guess the first 2 things I would check are:

1) Is the power supply correct without the dongle?
2) Is the reset pin high without the dongle?

Regards

John Samperi

********************************************************
Ampertronics Pty. Ltd.
11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA
Tel. (02) 9674-6495       Fax (02) 9674-8745
Email: john@ampertronics.com.au
Website  http://www.ampertronics.com.au
*Electronic Design * Custom Products * Contract Assembly
********************************************************

At 07:56 AM 3/31/2006, you wrote:
>Hello there
>
>
>I'm having some weird issues with an Atmega8 based board where the
>processor won't start the program unless the
>avrisp dongle is connected.
>
>
>You can see the circuit here 
><http://www.potemkin.org/uploads/Pid/arduino_rs232_v2.png>
>
>
>do you have any suggestions?

>thanks!

Is the power circuit the same as the USB version? (regulator?)

That 100uf on the output of the regulator might make vcc rise a little too 
slowly. Turning on the BOD might help.
But, you don't really need that cap, and it can hurt regulation. 
Try  putting in a 2.2 uf tantalum instead.

Just a possibility...

On 1 Apr 2006, at 23:03, Henry Carl Ott wrote:

> At 07:56 AM 3/31/2006, you wrote:
> >Hello there
> >
> >
> >I'm having some weird issues with an Atmega8 based board where the
> >processor won't start the program unless the
> >avrisp dongle is connected.
> >
> >
> >You can see the circuit here 
> ><http://www.potemkin.org/uploads/Pid/arduino_rs232_v2.png>
> >
> >
> >do you have any suggestions?
> 
> >thanks!
> 
> Is the power circuit the same as the USB version? (regulator?)
> 
> That 100uf on the output of the regulator might make vcc rise a little too
> slowly. Turning on the BOD might help. But, you don't really need that cap, and
> it can hurt regulation. Try  putting in a 2.2 uf tantalum instead.
> 
> Just a possibility...
I would agree - does it start if you press the reset button?

George Smith

On Mar 31, 2006, at 4:56 AM, Massimo Banzi wrote:
>
> I'm having some weird issues with an Atmega8 based board where the
> processor won't start the program unless the
> avrisp dongle is connected.
>
>
> You can see the circuit here http://www.potemkin.org/uploads/Pid/
> arduino_rs232_v2.png
>
> the rs232 interface part is not installed.
>
> I've checked and the fuses are programmed correctly (there are about
> 1500 usb boards that we sold with the same fuse settings)

I think my friend just bought one of these; I could look at it on my  
scope and see if I can see anything.
Does the unit come with a bootloader or something?

On Mar 31, 2006, at 4:56 AM, Massimo Banzi wrote:
>
> I'm having some weird issues with an Atmega8 based board where the
> processor won't start the program unless the
> avrisp dongle is connected.
>
>
> You can see the circuit here http://www.potemkin.org/uploads/Pid/
> arduino_rs232_v2.png
>
> the rs232 interface part is not installed.
>
> I've checked and the fuses are programmed correctly (there are about
> 1500 usb boards that we sold with the same fuse settings)
>
> it also happened a few times with some usb boards that when they are
> powered via the external power supply they have troubles starting up
> while when powered by the USB they work correctly.
>
>
I took a look at the power-up on a USB one configured for external  
power. This board has a 47uF aluminum cap before and after the  
regulator, rather than the 100uF cap shown in the schematic.

Starting it up with a 12V/500mA brick by connecting the brick and  
turning on the switch on the power strip I got the attached trace at  
the output of the regulator. Notice the large burst of trash. At  
times (especially when turning the supply off) it was a bit in excess  
of 5V!

Your input cap of 47uF is probably just fine.

You might want to reduce the output cap size.

[ See Linear Tech's app note AN88 on the overvoltage transient  
problems caused by using ceramic input capacitors: http:// 
www.linear.com/pc/downloadDocument.do?navId=D4125 ]

Hi you Quartz and CKOPT tamers out there ;-)

I came across a nice set of documents about Crystal oscillator design 
located at: http://gaia.ecs.csus.edu/~bist/pll_team_docs/papers.html

The fist one (by Vittoz et. al.) is a little bit on the theoretical 
side, but the "Fox files" counterweight this with short practical 
application notes.

If you look at Vittoz' short CV at the end of the first document, you 
understand his 'professional fable' for ultra low power designs.

Have a nice read,
Stefan