Quote: Originally Posted by Ale
The errors can be due to some noise in power supply, or the resistor divider mounted too far from max232 pin. Try to filter +5V of max232 with a couple of capacitor 10uF+0.1uF.
Well, I completely agree that it looks more like a periodic spike than a threshold problem, and I'd really like to get rid of it first. Regarding my power supply, well it's err... a 4.5V battery, so I guess it's rather stable, but maybe I'm mistaken. I have a 0.1uF but I could add a 10uF if you think i would improve something - obviously you have much more experience than I do :-)
Here's a picture of my test breadboard. Well, OK, I'm a bit ashamed of the look, but it helps changing the values around :-)