Clarke, K1JX have had the idea and pointed me to this device: https://www.adafruit.com/products/2479
There are few advantages over a WLAN CAT interface:
- cheaper interface
- less power needed for the interface
- less power needed for the iPad
- more reliable connection
On the other hand, you have to build your own interface. The signal lines need to be inverted. For testing I used a simple 74HC4049, powered from the 3.3V voltage regulator on the Adafruit board. The KX3 works fine with this level. Other transceivers may need a MAX232.
Some hints for the Bluefruit LE device:
- make sure you are using the latest firmware
- it uses a fixed rate of 9600 baud on the UART side
- you have to invert input and output signals
- it uses always hardware flow control --> connect the CTS pin on the board to ground, if you don't like to use it
To use it on your iPad, go to the TRX Control section and push the "Scan BT" button. Found supported interfaces will be listed in the table. Select the interface you want use. Press the "Connect BT" button or go to the K3/KX3 control screen if you want to use it. Here you will find a "Connect BT" button as well.
For info: Apple don't allow us to use a direct USB connection to external devices. Even simple Bluetooth devices are not well supported, we have to use LE (Low Energy) interfaces only.