Pixhawk telem2 communication

Hi, I just got a pixhawk (plus buzzer and safety button).
What I want to do is that connect pixhawk to PC (and 3G communication board in the future) and communicate MAVLink packets.

I connect usb micro cable to feed electricity (5V 2A) , buzzer, safety button and serial cable from telem2 connector to PC, and watch the packets pixhawk sent.
Then buzzer started to warn “Low voltage” (I forgot the exact message in MAVLink packets, but it said something like that).
What should I do? I bought power module cable but I do not have buttery yet.

Now I disconnect the buzzer and watch some MAVLink packets (Heartbeat) pixhawk sent.
I want to get some more packets

  • ATTITUDE (#30)
    So I send some messages
  • DATA_STREAM (#67)
    I did not get the packets I want except when I sent REQUEST_DATA_STREAM with reqest_stream_id=1 (MAV_DATA_STREAM_RAW_SENSORS) , in that case pixhawk sent many packets.
    How can I get the packets (#33, #36, #66)?

I am fairly new to pixhawk so I might be asking some stupid questions…
Thank you in advance.