Cannot loopback UART with RN42-SM Socket module
I am using the UART (not RS-232) interface on the RN-42-SM Socket Module. My initial goal is to do a loopback test sending characters at 115200 from PC over Bluetooth connection, looping back from Tx to Rx on the RN-42, and back to PC over Bluetooth.
I modified the board as follows:
1. Removed R6 and R8
2. Connected CTS and RTS on Header B (tied J1-3 to J1-4)
3. Connected Tx and Rx on Header B (tied J1-1 to J1-2)
4. Supplied power: 3.3V on Header A pin 11; GND to Header A pin 12
I can open a connection using a PC terminal emulator to the BT COM port at 115200 baud, and the green LED goes on steady when this is done. When I type characters in the terminal emulator, I see them with a scope probe on the RN-42 UART Tx-Rx pins, and the bit time corresponds to 115200. However, the characters are not returned back over the BT connection. I noted that the voltage level on the Tx-Rx pins is only 2V when high, which is below the minimum 2.8V
Can anyone help with what the problem may be?
Thanks in advance,