WiFi hotspot frecuency

How can I change default WiFi frequency from 5GHz to 2,4GHz?

Once you are connected to Erle-Brain, you need to change hostapd.conffile:

@localhost:~$sudo nano /etc/hostapd/hostapd.conf

This is how it looks like:

# Basic configuration

interface=wlan0
ssid=erle_snappy

# WPA and WPA2 configuration

macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=3
wpa_passphrase=holaerle
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

# Hardware configuration
#driver=rtl871xdrv
#driver=nl80211
ieee80211n=1
channel=40
#hw_mode=g
hw_mode=a
device_name=RTL8812AU
manufacturer=Realtek

You need to change channelvalue from 40 to 9. And Uncomment hw_mode=g and comment #hw_mode=a:

# Hardware configuration

ieee80211n=1
channel=9
hw_mode=g
#hw_mode=a
device_name=RTL8812AU
manufacturer=Realtek

Finally, don't forget restarting Erle-Brain!