DreamScreen V1 has a BLE interface and can be controlled by hardware with BLE master capability. The attached document has information about Service and Characteristics that are exposed and the commands to read and write to Dreamscreen.
You mustn't denote the end of write/read command by "\r".
I've found place where "\r" appears - DS denote the end of notification. As I can see, DS always send notification with 20 bytes of data. Real data in these 20 bytes - is before "\r". (Sample code for extracting data in Python - data.slplit()).