Android Question Print usb esc/pos printer

[roby128128]

Good morning and thanks in advance to those who want to help me, I'm printing via usb and esc/pos printer with the example /ESC/POS example , the software works for a while then even if the printer is connected it does not print for a while and then resumes printing when it decides, I tried with three different models, same defect, also on the android system I have two printers install usb, how do i choose which one to print on? finally I attach the qrcode string that I send and it doesn't work Thanks:
Example QRcode string:

Dim sito As String ="http://www.google.com"
Dim lst As Int=sitowe.Length+3
printer1.WriteLine(Chr(29) & Chr(40) & Chr(107) & Chr(04) & Chr (00) & Chr(49) & Chr(65) & Chr(50) & Chr (00) & Chr(29) & Chr(40) & Chr(107) & Chr(03) & Chr(00) & Chr(49) & Chr(69) & Chr(48)  & Chr(29) & Chr(40) & Chr(107) & Chr(03) & Chr(00) & Chr(49) & Chr(67) &  Chr(05) & Chr(29) & Chr(40) & Chr(107) & Chr(lst) & Chr(00) & Chr(49) & Chr(80) &  Chr(48) & sito)

 

[roby128128]

Sorry, I'm only reading now that the library is demo, so it prints one minute every two, but for the other questions, I'm waiting for an answer, thanks.