Today, I conducted testing on the power supply. Upon observing a voltage drop below 3.5V, the Raspberry Pi initiates a reboot sequence. Additionally, I adjusted the voltage thresholds within the Atmel device from 3.0V to 3.5V. Configuring the GPIO pin to maintain a high level for the Atmel in `/etc/rc.local' remains on the to-do list. Without running the cam-python-script, the charging of the Li-ion-cell works, it is getting enough power. But with powering the FTP screen, the loading circuit delivers not enough power to run everything.
I also started translating this site from german to english.