Forensic acquisition of an Android device using open source tools requires you to connect the device to a forensic workstation. Forensic acquisition of any device should be conducted on a forensically sterile workstation. This means that the workstation is strictly used for forensics and not for personal use.
Note that any time a device is plugged into a computer, changes can be made to the device; you must have full control of all interactions with the Android device at all times.
The following steps should be performed by you in order to successfully connect the device to a workstation. Note that write protection may prevent the successful acquisition of the device, since commands may need to be pushed to the device in order to pull information. All the following steps should be validated on a test device prior to attempting them on real evidence.