Telemetry allows you to know what is happening on your aircraft while you are flying it. Among other things you can receive battery voltages and GPS positions on your transmitter.
Telemetry can be either always on, or enabled when armed. If no serial port is set to be telemetry-only then telemetry will only be enabled when armed.
Serial ports use two wires but HoTT uses a single wire so some electronics are required so that the signals don't get mixed up.
Connect as follows:
```
HoTT TX/RX -> Serial RX (connect directly)
Serial TX -> 1N4148 Diode -(| )-> HoTT TX/RX (connect via diode)
```
The diode should be arranged to allow the data signals to flow the right way
```
-(| )- == Diode, | indicates cathode marker.
```
As noticed by Skrebber the GR-12 (and probably GR-16/24, too) are based on a PIC 24FJ64GA-002, which has 5V tolerant digital pins.
Note: The softserial ports are not listed as 5V tolerant in the STM32F103xx data sheet pinouts and pin description section. Verify if you require a 5v/3.3v level shifters.
MSP Telemetry simply transmitts MSP packets in sequence to any MSP device attached to the telemetry port. It rotates though a fixes sequence of command responses.
It is transmit only, it can work at any supported baud rate.
MSP telemetry is currently only output on serial ports that are set to MSP, NOT telemetry.
This will likely change in the future so that the MSP telemetry uses ports configured as telemetry just like the other providers do.