T-board test with atmega 328

[Nixies]

Hello,
I'have aquired the t-board recently and I have tried the first helloworld. The problème is that the clock, supposed to generate 1 second flashing led is not that accurate. I'm working without crystal, so I modified the commande F_CPU with the value 1000000 (this is the value which allows me to approach as much as possible to the second). If I compare the pace of this 1 second clock, it is slighly different than the one of my Watch. I don't understand why. I've tried it under linux (avr-gcc + avrdude) and Under Windows 7 but the result is the same, a second a bit longer than one second
Is it possible that the problem comes from the fact that I don't use any cristal ?
I've tried with a cristal of 4 MHz, modifying the F_CPU with 4000000 but it does not work, probably because I need to configure the fuse with external cristal, but I don't know how to do it

Help from you should be really welcome
Thank you very much.
Nixies

[ag]

Hi Nixies,

If I compare the pace of this 1 second clock, it is slighly different than the one of my Watch.

How much different?

I've tried with a cristal of 4 MHz, modifying the F_CPU with 4000000

According to the datasheet, the internal clock of the ATMega328 is 8 MHz, so I don't think you can improve the tolerance by using a 4 MHz external crystal.

but it does not work, probably because I need to configure the fuse with external cristal, but I don't know how to do it

The nice thing about the Arduino IDE is that beginners do not have to worry about setting fuses. I recommend you use the Arduino IDE until you have gained more experience.

Regards,

[Nixies]

Hello Ag,
To be honest I want to avoid Arduino, because I really want to understand what is Inside the µc.
Difficult to describe the difference, but if if want to make a clock with this kind of programme, it will quickly drift
I modified the fuses by means of AVR Studio (Menu Tools -> Device programming) to use the 4 MHz Crystal, that's why change the F_CPU. In the meantime I read some docs and I saw that I did not use the good fuse option. I will try again. I let you know.
Ag, do you have the possibility to try this king of code ?

Anyway, thank you very much.
Nixies

[ag]

Hi Nixies,

I do not have a T-Board, but I do have an Arduino with a ATMega328 (Duemilanove), which is basically the same. So yes, I can test such code. That is why I wanted to know how far off your timing is running. Fuse settings are always a problem for beginners, but with reading the docs to find out how, you are going in the right direction. You might want to visit AVR Freaks at http://www.avrfreaks.net to get some good beginners tutorials and assistance.

Regards and LoL,

[Nixies]

Thank you Ag for this link. I will take a look to it.
Speek to you later.
Regards,
Nixies

[Nixies]

I've tried with the second T-board, embedding a ATtiny 84, and the second is a second
I will try to search why it is not the same with the atmega328.

[Nixies]

I changed the mega 328 and it is working.
Honestly I don't know why it did not work with the first one. Probably the fuses