This interface is built on perfboard and meant to be mounted onto a Raspberry Pi running direwolf. Connections to the soundcard and radio are through breakout cables so that the interface can be configured for different radios and soundcards.

Screw Terminal Connections

Orient the board so that the screw terminals are on top as in the picture, terminal #1 is on left and terminal #7 is on the right.

1. PTT (from radio)
2. Gnd (from radio)
3. Gnd (from soundcard)
4. Spkr+ (from radio)
5. Mic (to sound card)
6. Mic+ (to radio)
7. Left channel (from sound card)

Breakout Cables

Radio Breakout Cable (Kenwood, Baofeng, etc)

3.5mm TRS Connector

• Tip
• Ring, Mic+
• Shield, PTT

2.5mm TRS Connector

• Tip, Speaker+
• Ring
• Shield, Ground

Soundcard Breakout Cable

3.5mm TRRS Connector

• Tip, Left channel
• Ring, Right channel
• Ring - Ground
• Shield - Mic

Direwolf Configuration

• PTT is on GPIO 13
• DCD is on GPIO 4

Schematics

• Schematic
• Fritzing

Resources

• Super Simple APRS Position Reporter｜Midnight Cheese
• APRS – Raspberry Pi Virtual TNC – WCARES
• APRS RX/TX I-Gate and Digipeater for less than $100 - N1AAE
• Soundcard interface - (including PTT) for Baofeng UV5R and other cheap handhelds
• Direwolf - APRS Box Documentation
• direwolf/Successful-APRS-IGate-Operation.pdf at master · wb2osz/direwolf
• Converting a CM108 USB fob for amateur radio use
• LTV-847C Datasheet
• A Simplified USB Sound FOB Modification
• How To Modify A CM108 for Allstar latest version - allstar setup.com %
• Modifying the SYBA UAUD CM119 based USB audio adapter for use as Asterisk USB radio interface
• usbfob.pdf
• GitHub - eleccoder/raspi-pico-aprs-tnc: A modem/TNC to generate the AFSK audio tones for sending APRS messages using a Raspberry Pi Pico
• audio - How to DIY BaoFeng radio-to-soundcard cable? - Electrical Engineering Stack Exchange
• Adding PTT on USB Soundcard
• ZS2EZ Soundcard Interfacing
• Raspberry Pi Datasheets