Arduino 3v3 building

Hi,

Sorry for dumb questions. I have built several Arduino clones with Atmega168 and 328's. These were 5V/16MHz ones. Now i want to make a 3,3V/8MHz board for developing purposes. I have built it, with 8MHz crystal, appropriate power circuit, and so on. I grabbed an Atmega168 which had an 5V/16MHz bootloader installed. Put in the 3,3V board, and wanted to write a 3,3V bootloader in it, but Arduino IDE cannot communicate with the uC. The uC works great in the 5V developer board, i can write any bootloader in it, or upload programs, but in the 3,3V board, it does nothing. No serial communication, no communication via the ICSP header. No miswiring, i checked 100 times. I use DAPA programmer, which works great with the 5V board.

I tried erase the uC with uisp, but no success.

Has someone any ideas, what can be the problem?

(Can it be that i must re-fuse the uC for 3,3V bootloader writing? Or isn't the Atmega168 3,3V tolerant? My programmer, and RS232 converter use 5V TTL levels.)

Thanks for any help!

The serial port timings will be different because you halved the clock speed. You might need to edit the baud rate in your "boards.txt" to match (maybe create a new entry for your Frankenstein board...)

PS: What voltage does your programmer put out? You're not supposed to apply more than Vcc+0.5V to any I/O pin (although at low currents probably nothing bad will happen - they have protection diodes to clamp the voltage).

Hi,

I don't use serial port yet, first i only want to write a loader into the uC at 3,3v so i will have a 3,3V uC to experience serial port problems with ;)

My programmer works at 5V TTL levels, so it theoretically damages the uC, but when i pull out the uC from the board, and put back to the 5V test board, it operates normally. I have luck :)

Thanks for the suggestions - i accept any further advices :)

I have a a stripboard 328 running 3,3V with 8Mhz x-tal.

What I do is:

When progamming (burning bootloader etc) I feed the stripboard Arduino with 5 volt, and then I can go back to using it in the intended 3,3V mode.

That way I don't need level-converters on the programming lines. Remember the Atmega328 is only rated for VCC + 0,5 Volt on the pins.

I have tried to program the uC from 5V and 8MHz crystal... But nothing changed. :S

Is your 8MHx X-tal broken ?

ColT:
I have tried to program the uC from 5V and 8MHz crystal… But nothing changed. :S

I tried to see what board you’re selecting in your IDE’s menu but it’s too cloudy today.

I can tell you that you can’t keep on using the same board in the menu if you change the crystal. The serial baud rate will be wrong.

Hi,

I selected Arduino Pro or Pro Mini, 3,3V/8MHz, with Atmega168

But when i try to read fuses with uisp, the same command which works with the 5V board, it cannot read, and gives back all signatures 0x0ff. I think it cannot communicate. And i use DAPA programmer, it doesn't use any serial communication, it is on parallel port.

ColT: But when i try to read fuses with uisp, the same command which works with the 5V board, it cannot read, and gives back all signatures 0x0ff. I think it cannot communicate. And i use DAPA programmer, it doesn't use any serial communication, it is on parallel port.

Are you running at 3.3V? Vcc needs to be 5V for parallel programming.

Tried with Vcc=5V and 3,3V too. Nothing :S

Hell's fire! Solved. One of the 2 capacitors on the crystal was short. There were no clock...

Thnaks for the help!