Thanks MikMo.
Concerning ground, unfortunately, that's ok.
Sorry for the bad cut/paste, you're right, I mean
(i = 0; i < 20; i += 1)
The signal levels on the Velleman card is RS232 and I use max232 adapter.
I'm suspicious about arduino when the serial is configured in 2400 bps mode or maybe, it's my adaptator ?? :-?