The TTL_GPS model of the Bluefly is designed to add a vario and GPS to a Kobo running xcsoar by soldering it to an internal UART serial port. For technically savvy pilots this has been a popular way to build a powerful and reliable flight instrument. The previous TTL_GPS model was released in late 2021, but the chip crisis has meant that the main processor is no longer available. The new v22 TTL_GPS models use the same PIC32MM processor as the earlier v22 bluetooth models and share most of the same codebase.
Today I release two v22 TTL_GPS models: a base model BlueFlyVario_TTL_GPS_v22 to replace the v12.2 version released last year, and a new enhanced model BlueFlyVario_USB_TTL_GPS_IGC_v22 which adds a USB interface and onboard IGC memory recording.
Base Model BlueFlyVario_TTL_GPS_v22 Hardware Design
Most people installing the Bluefly on a Kobo will want this base model. It is cheaper and offers the same functionality as earlier versions.
The base model TTL_GPS_v22 is functionally very similar to the last v12.2 model. It has the same L96 GPS, shares the same form factor, and primary TTL_GPS pinouts. Most users will connect it to the Kobo via the UART 1 TTL port. Other noteworthy elements of the hardware design are:
- It uses the new PIC32MM microcontroller as the other v22 models.
- There is a new all metal button that is more robust, but still needs to be used carefully. Most users will not use the button as the vario powers on as soon as the TTL port has power from the Kobo.
- On the back the RST and GND pads can be shorted while the vario is powered on to reset all settings to default. Make sure to deliberately power it off using the button to save the new settings.
- There are a few ways to use V_Backup if you really think you need it, but I do not recommend connecting it or closing the solder jumper unless you have read the L96 datasheet and know what you are doing.
- The programming pads are also connected to UART 2, which caries the serial communication from the microcontroller to the GPS.
- The UART 3 pads on the back provide another TTL input/output like UART1. If I release firmware updates you will need to interface with these to update the firmware.
- There are quite a few components not populated as the USB_TTL_GPS_IGC uses the same board.
Enhanced Model BlueFlyVario_USB_TTL_GPS_IGC_v22 Hardware Design
There are a few reasons why you might want the enhanced model:
- The addition of onboard IGC recording means that you can record a signed IGC file while the vario is connected to your Kobo. You might use this for a backup, or even as your primary file. This is able to be downloaded via the USB port using the BFVDesktop application or GPSDump. Read earlier blog posts about the Bluetooth models to understand how IGC recording works on the Bluefly.
- Some pilots might want to connect the Bluefly via the USB port to a windows or android device running xcsoar or xctrack. You can close the USB PWR header to enable the vario to be powered from the USB port.
- However, warning: If you close this header and power the Bluefly from the USB-C interface while the Bluefly is connected to the Kobo, but the Kobo is powered down, then you will fry either the Kobo or the Bluefly. I recommend only closing this header if you do not intend to connect the Bluefly to a Kobo.
- It is ok to have your Bluefly connected to and powered from the Kobo via UART 1, and then plug in a USB cable to the USB-C interface on the Bluefly (but with USB PWR not closed) This will allow you to transfer data from the Bluefly via the USB-C interface (adjusting the settings, downloading IGC files, updating firmware).
- Some pilots might want to use this model connected via a USB cable to an external battery to use as a stand alone vario without a display. You could solder a switch across USB_PWR.
Like the base model, most users will connect it to a Kobo via the UART 1 TTL port. Other noteworthy elements of the hardware design are:
- The USB-C interface connected to UART 3 mirrors UART 1.
- The USB power connection to V-Backup is only for advanced users that know how the L96 V_Backup works.
The firmware builds on the earlier v22 models. It is functionally very similar to earlier versions.
What is in the bag
The bag for both models contains only vario module, a small piece of neoprene, and some heatshrink to hold the neoprene in place.
You will need to add your own wires and enclosure (if you want one).
Assembly
See the assembly instructions for the previous version.
