Cannot get serial plugin to work

I’m having trouble making the serial module play. All I get is jibberage on the screen at any baud rate and cannot send. I am using the following setup.

Meshtastic 1.2.59 (serial_plugin)
Heltec v2.1 radios
USB to Serial adapter

Also getting erroneous temp/humidity readings using DHT11. Initial reading is good. Subsequent readings are way off.

Thanks in advance for any help. Jim

Please share more about your configuration, how you have devices setup and either a schematic or a description of a schematic for your circuit.