Description
We have built a Bluetooth-enabled and APRSdroid-compatible digital interface (KISS TNC) for less than 15 USD (for the fully-loaded make including cables). We call it the KISSLink v1.
This digital interface can be powered from the USB 5V or the inbuilt battery.
Schematic
RX path simulation (AF front-end)
Motivation
https://store.mobilinkd.com/products/mobilinkd-tnc4 is the BEST but it is expensive and hard to source (from many global locations).
Think upwards of 150 USD for getting a fully-loaded Mobilinkd TNC4.
BOM
Raspberry Pi Pico 2W - 610 to 750 INR
Ambrane 3.5mm to 3.5mm male aux stereo cable TRS - 130
2.5mm to 3.5mm aux stereo cable - 250 (element14)
PCB - 150
Components - 70
Case - 100 INR
Good quality 18650 cell - 150 to 200 INR
Total - ~1375 INR or less (< 15 USD)
Notes
We considered using "1000mAh" 14500 cells for their compactness (AA sized) but ultimately went in for much higher capacity 18650 cells.
The device can be powered either from the internal battery or via the Pico USB port. When charging the battery, use the externally exposed TP4056 module's USB connector. Do not connect both USB ports simultaneously!
Pros
FREE hardware (Gerbers + BOM + CPL + enclosure design file)
Open schematic!
No cables to make. No cables to cut up!
THT audio connectors which can handle rough handling
We may even open-source the firmware part (currently requires a support license) after sales target are hit ;)
Currently Supported Protocols
KISS over Bluetooth SPP
KISS over Serial USB
Future
- Enable and test BLE support in the firmware for iOS