Digital output voltage - Duemilanove vs standalone

Other Hardware 3rd Party Boards
1

Hi,

I'm transferring a project from a Duemilanove board to a standalone bare bones Atmega 328.

One strange issue is the voltage at the digital pins. On the Duemilanove it seems to be about 25% higher (via a scope, can't seem to get a peak reading from my multimeter)

It's the difference between an LED with no resistor being uncomfortably bright, and the same LED being lit, but not especially brightly.

The standalone is being powered by a 7805 being fed by a chunky 12v supply with 100u capacitors before and after it, with just over 5v at Vcc and AVcc.

The project is using digital output pulses to trigger a modular synth - the pulses from the Duemilanove work just fine, from the standalone they're patchy.

Can you think what might be causing the reduced voltage?

I don't know if it could help with troubleshooting, but I'm also finding the standalone Serial port behaving strangely - it reads MIDI in (which should be 31250 baud) while set at 15625 baud - as if it's running at 8mhz rather than 16 - despite being clocked by a 16mhz crystal. Could this be caused by programming it with a 3.3v FTDI cable?

Thanks for reading this far!

2

despite being clocked by a 16mhz crystal

When you prepared the standalone processor, what fuse settings did you use?

3

Not sure, bought a 328 with a bootloader already on it.
I can get sketches to load by using the Arduino Pro 3.3v 8mhz setting.
I think it's because I accidentally bought a 3.3v FDTI cable.

4

Not sure, bought a 328 with a bootloader already on it.

From? Have a link?

Do you still have the original Duemilanove processor?

5

The FTDI cable shouldn't affect the sketch upload settings. Perhaps the bootloader in the standalone is configured to use the internal 8MHz oscillator? What happens if you remove the external crystal?

6

LED with no resistor being uncomfortably bright,

Never never never, power an LED without a resistor. You will damage your arduino.