Ok, a couple of problems ....
You are trying to read the text of the button, not the combobox i.e.
Select Case cmd_sensor_t7770a.Text
Case t7770a1006 'Calls sub from Module_sensor
Sensor_t7770a1006_get
Case t7770a1022 'Calls sub from Module_sensor
Sensor_t7770a1022_get
Case "t7770a2004" 'Calls sub from Module_sensor
Sensor_t7770a2004_get
Case t7770a2012 'Calls sub from Module_sensor
Sensor_t7770a2012_get
Case t7770a3002 'Calls sub from Module_sensor
Sensor_t7770a3002_get
End Select
You should be reading the contents of the associated combo box as so:
Select Case ComboBox_t7770a.Text
Case t7770a1006 'Calls sub from Module_sensor
Sensor_t7770a1006_get
Case t7770a1022 'Calls sub from Module_sensor
Sensor_t7770a1022_get
Case "t7770a2004" 'Calls sub from Module_sensor
Sensor_t7770a2004_get
Case t7770a2012 'Calls sub from Module_sensor
Sensor_t7770a2012_get
Case t7770a3002 'Calls sub from Module_sensor
Sensor_t7770a3002_get
End Select
Further, you should also be comparing the values as text strings, as you have it written the code compares the cases to variables. i.e. you text comparisons must be in quotes as follows:
Select Case ComboBox_t7770a.Text
Case "t7770a1006" 'Calls sub from Module_sensor
Sensor_t7770a1006_get
Case "t7770a1022" 'Calls sub from Module_sensor
Sensor_t7770a1022_get
Case "t7770a2004" 'Calls sub from Module_sensor
Sensor_t7770a2004_get
Case "t7770a2012" 'Calls sub from Module_sensor
Sensor_t7770a2012_get
Case "t7770a3002" 'Calls sub from Module_sensor
Sensor_t7770a3002_get
End Select
You have quite a few things to correct, but once you do it should work as desired.