破解 GPO 746 旋转电话 - SegmentFault 思否

Rotary dial telephones for electronics learning: They can be disassembled and serviced (originally rented). Online communities exist for sharing knowledge. The project is to make a GPO 746 rotary dial telephone that plays a random song when the handset is picked up.
- Logical core: The D92732 circuit board connects components. For this project, only the switch hook (signals handset picked up) and handset receiver (plays music) are focused on.
Getting inside the phone: Use a flathead screwdriver to loosen the screw at the back held by a spring and nut. Take photos and disconnect all wires.
Brute-forcing switch hook terminals: Use a multimeter to check connectivity between 19 choose 2 = 171 combinations. In this phone, it's terminals T3 and T6. The meaning may be reversed.
Handset receiver: Unscrew the handset to identify the red and green wires for the receiver.
Wiring the terminals: Connect the red and green handset receiver wires to T11 and T13. Connect the brown and black switch hook wires to T3 and T6.
Wiring the audio breakout board: Red to sleeve, green to tip. Solder the Teensy Audio Shield to the Teensy using pin headers and connect the audio breakout board with a 3.5mm audio cable.
Wiring the Teensy: Red and white connect to the battery pack's ground and Vin pins. Brown and black connect to the switch hook terminals and ground. Use the correct Vin pin as the battery pack exceeds 3.3V.
Battery pack: Connect the red and black wires from the Teensy to a 3xAA (4.5V) battery pack and toggle switch.
Software considerations: Append code for reference. Use teensy-loader-cli to transfer a compiled image after disconnecting from the battery pack. Wrap everything in a Nix flake.
Costs: Spent about £300 including tools and components. Tools cost £165 and the total for other items is £311. An option is to visit a local hackerspace for free or cheap tools and components.
Final thoughts: Felt emboldened to fix things around the house. Want to get the rotary dial, ringer, and microphone working. Overall satisfied with the result.
Inspiration & resources:
- [britishtelephones.com] for history and circuit diagrams.
- [YouTube: "Make your own wedding audio guestbook"] for inspiration.
- [YouTube: "Beginner’s Guide to Soldering Electronics"] as a favorite soldering guide.
- [YouTube: "Shenzhen: The Silicon Valley of Hardware"] by Andrew "bunnie" Huang.
Appendix:
- Tools: TS101 soldering iron, Omnifixo "third hand" tool, multimeter, wirestrippers, wire cutters, flathead screwdriver.
- Materials: GPO 746 (UK), Teensy 4.0/4.1, Teensy Audio Shield, microSD card, 22 AWG wire, soldering materials, micro-B USB cable, 3.5mm audio cable.
- Optional: 3xAA battery pack, toggle switch, pin headers and jumper cable, 3.5mm jack breakout board, fork terminals.
- Code: Check the repository for the latest version. It initializes various components and handles the random song playback based on the switch hook state.