A custom Bluetooth adapter lets the factory-option DiamondTel Model 92 in Jeff Lau’s 1993 Mitsubishi 3000GT VR-4 handle calls again—but it does not revive the car phone’s obsolete cellular service. Instead, the adapter takes over the original handset interface and routes calls through a modern cellphone paired over Bluetooth Hands-Free Profile (HFP).
What the adapter brings back—and what it does not
The DiamondTel Model 92 was designed for 1G analog AMPS service. Jeff Lau says that service had become unavailable in the United States by 2008. His project does not reconnect the original transceiver to a cellular network; a paired modern cellphone supplies the call connection.
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What remains is the distinctive in-car phone experience. Rather than hiding a Bluetooth headset in the handset and wiring only its microphone and speaker, Lau reverse-engineered the proprietary interface between the DiamondTel handset and transceiver. His adapter emulates the handset’s behavior and communicates with the cellphone using HFP.
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The project’s intended features include handset dialing and SEND behavior, display information, original-style tones, volume controls, call timing and directory features. Hackaday’s 2023 coverage also reports that the conversion retains radio muting and steering-column controls. These are project-described capabilities, not an independent performance test.
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How the vintage handset connects to a modern phone
- The adapter connects inline. It sits between the DiamondTel handset and its transceiver, rather than replacing the handset with a generic Bluetooth earpiece.
- The transceiver continues to supply power. The original transceiver retains its existing power behavior while the adapter implements the handset interface.
- The adapter pairs with a cellphone over HFP. Once paired, the modern phone provides the connection for incoming and outgoing calls; the vintage handset remains the car’s user interface.
This division is the important distinction: the old hardware supplies the controls and car-phone character, while the modern cellphone handles the network connection.
How this compares with a simple Bluetooth-headset conversion
| Approach | What it does | Trade-off |
|---|---|---|
| Headset audio hack | Connects Bluetooth audio to the handset’s speaker and microphone. | Less involved, but does not reproduce the phone’s display, buttons, menus or broader integration. |
| Lau’s inline adapter | Reverse-engineers and emulates the handset interface, with a Bluetooth HFP link to a modern cellphone. | Preserves more of the original controls and behavior, but requires custom circuit design and substantial firmware work. |
This is a comparison of approaches, not a head-to-head performance test. The project documentation does not establish a current off-the-shelf adapter or retail kit.
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Will the adapter work with other vintage car phones?
Do not assume so. The wired handset interface is proprietary, and the project documentation identifies only the DiamondTel Model 92 and Mitsubishi Model 1500 as known compatible vintage models. A phone from another manufacturer—or even another model from the same era—may use a different interface.
HFP support is the relevant Bluetooth feature for the modern cellphone, but the project owner says only a small selection of phones received basic testing and does not guarantee compatibility with every phone. Check the project’s current compatibility notes before choosing either end of the connection.
Rank #3
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- 【Dual Connection】The portable Bluetooth stereo adapter can be paired with 2 devices at the same time. You can enjoy your music and never worry about missing any calls. Once paired, the car receiver will automatically reconnect to your last paired Bluetooth devices, as long as they are within the wireless range.
What building the adapter involves
The documented electronics include a BM62 Bluetooth module, a PIC18F27Q43 microcontroller and analog audio circuitry. This is a DIY electronics project, not a plug-in cable or complete, guaranteed kit.
- Hardware skills: soldering and careful electronics work.
- Verification and troubleshooting: a multimeter and oscilloscope are called for in the build guidance.
- Firmware tools: MPLAB X and a PICkit 4 programmer/debugger or equivalent are named for programming the microcontroller.
- Documentation caveat: the author says the information is extensive but not a complete step-by-step guide.
The project has evolved beyond the plug-in prototype covered in 2023 reporting. The repository describes an updated standalone design using custom PCBs hidden inside the original transceiver, but says the documentation is not fully updated and the design remains in progress. Consult the current project materials before attempting a build; prototype coverage should not be mistaken for finished instructions for the newer version.
Rank #4
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- 【Smart FM Radio Transmitter】 - Just match this adapter’s FM frequency with your car radio to enjoy wireless music from your phone. The LED ring glows blue for easy visibility at night and shows power status. The sleek design fits all standard cigarette lighter sockets.
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- 【Music Control at Your Fingertips】 - Take full command of your playlist without touching your phone. Convenient left/right track buttons allow you to skip to the next or previous song easily. Supports music pause/play, and long-press left/right to adjust FM broadcast frequency.
Where to check the project and its terms
Jeff Lau’s project page explains the restoration goal and project status. The GitHub repository is the technical reference for the architecture, compatibility notes, components and build information. Hackaday’s April 13, 2023 coverage describes the earlier prototype and retained vehicle integration; Hackster.io’s report also covers the HFP approach and model limitations.
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Lau makes technical information, hardware designs and code available for personal, non-profit use. Hackster.io describes the source as released under a custom no-commercial-use license. That is not permission to sell kits or treat the project as commercial open hardware.
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