If your wifi connections switches off after being connected for some time sometimes it may be fixed by disabling the power management so it never goes to power saving mode. Create the file /etc/modprobe.d/8188eu.conf
with this content:
options 8188eu rtw_power_mgnt=0 rtw_enusbss=0
Restart Raspbian and check those options with those commands:
$ cat /sys/module/8188eu/parameters/rtw_power_mgnt 0 $ cat /sys/module/8188eu/parameters/rtw_enusbss 0
0 Comments.