Piston Slap: New tricks for an old car phone (Part V)

In our last episode, we met Jeff, the man behind the Bluetooth-conversion kit for analog, in-car Mitsubishi cellular phones of the 1990s. If you want to follow in his footsteps, check out the open-source info and the build thread. If enough people motivate Jeff to make more modules (and ones for other vehicles) we will update this series once more. But for now, let’s learn a little more about the man behind this fantastic creation. 

SM: What motivated you to do the conversion in the first place?

Jeff: My Mitsubishi 3000GT did not have the car phone when I bought it. While searching for an owner’s manual on eBay, I stumbled upon a new-old-stock original sales brochure for the 1993 3000GT. When it arrived, I found a brief mention of a telephone accessory:

You may also install an available cellular telephone if you wish—complete pre-wiring is already provided. A fitting final touch in a place where meticulous attention has so obviously been paid to every last detail.

I had to have it, because this car was all about excessive amounts of early ’90s tech, and this was yet another optional piece that I was missing. There were unused factory connectors hiding somewhere in the car just waiting to fulfill their destiny. Armed with a photo of this excerpt from the sales brochure, I went to the 3000GT Facebook groups and forums to ask for info about this car-phone system, and if anyone had one they would sell.

Despite the evidence I had, nearly everyone (even 15+ year veterans in the community with years of buying/selling/part-outs) was telling me that there was no such thing as a factory car-phone accessory, or that it was just a dealer add-on where they would install any consumer car-phone system. There was nothing special about it, they said.

I eventually started tracking down info and evidence of the system and started the three-year journey of piecing together a complete system, including scoring a brand-new-in-box telephone).

Pretty soon after I imagined getting the factory car-phone system for my car, I started wondering if there was any way that it could actually be activated or modified to be fully functional. My plan was to fix/maintain it as a stock example of what the car was supposed to be, with all of its technology working as intended. I quickly learned that, since 2008, it’s impossible to activate service on analog cell phones and that there are no adapter/conversion kits available.

I initially started researching the possibility of building a Bluetooth adapter that connects to the original phone’s antenna port and simulates 1G analog service to the phone. This would have allowed the phone to remain fully functional, as original, while routing calls over Bluetooth to a paired cell phone. It also would have been compatible with any 1G analog car phone with a coax antenna port. I found technical explanations and original specs for 1G cell service, but I was absolutely lost on the electronics side of things. Still struggling to even find all the parts of the car phone system, I lost motivation and gave up on trying to figure out the 1G-cellular-to-Bluetooth-adapter idea. Maybe it was possible, but it was way beyond my electronics knowledge/skills.

The “easy” solution of hacking a modern Bluetooth headset into the handset was never an option for me. I wanted the display and buttons of the handset to be fully functional for an authentic experience. I specifically wanted the ability to dial a number on the handset, press send, and have it actually call that number. It was all or nothing for me. I’d rather have the original phone fully “working” without service than reduce it to a cosmetic shell around a Bluetooth headset.

About a year later I started wondering if I could somehow interface with the handset directly through its cord. I found renewed motivation and decided to get an oscilloscope just to see what I could figure out about those eight wires in the handset cord. This is where I started documenting the rest of my journey on the electro-tech-online forum. I got really lucky and was able to reverse-engineer much of how to control the handset in just over a week, with a simple proof-of-concept manually sending commands from my computer through a USB adapter and simple circuit to the handset.

Two weeks later, I had deciphered even more, and had my first proof of concept of software on a microcontroller being in control of the handset. This is about when I finally felt like this was actually possible, and I wasn’t going to settle for anything less than a final result that was practically indistinguishable from the original.

The rest is a year-long journey of details: figuring out how to work with a Bluetooth module, figuring out how to design the analog audio circuitry I needed to deal with all the audio/sounds, tons of programming of menus and features to replicate the behavior of the original phone, figuring out how to be compatible with the car’s hands-free system, etc. Much of the electronics part of this project was at or beyond the edge of my knowledge, so there was a lot of research, followed by asking questions on the electro-tech forum.

I’m extremely lucky and thankful that a couple of people took interest in my project, followed its progress, and answered my questions or offered suggestions. I don’t think I could have done it without their help. I think it worked out well because I was very proactive in researching and trying things first before asking for help, then I would use the responses to guide more research and make as much progress as possible on my own. I tried to be as self-sufficient as possible and only ask for guidance, not for complete solutions.

SM: What is your background? This kind of project clearly requires specific skills.

Jeff: Professionally, I’m a software engineer that primarily works on front-end web application development. I’ve been programming since I think the early ’90s, when I was a kid and discovered DOS batch files, then QBasic. I took programming classes in high school, and almost failed a few other classes because I would stay up too late programming silly games instead of doing my homework for other classes. But it worked out okay, because I landed my first “real” job as a programmer with only my high school diploma, and progressed from there.

The programming aspect of this car-phone project was very fun and comfortable for me, despite it being quite different from my day-to-day professional programming work.

My background in electronics is extremely limited and amateur. I had an electronics educational kit as a kid that I didn’t understand, but I could follow the instructions to make things. I also took an intro electronics class as an elective in high school. The electronics aspect of this car phone project was out of my league, and I had to learn almost everything along the way. I often procrastinated on solving hardware issues by continuing to develop more features in the software, like the games Snake (above) and Tetris.

SM: How did you get into cars? Into electronics?

Jeff: If I had to pick one pivotal moment that got me “into cars” as a hobby/enthusiast, it would probably be when I bought a new 2013 Jeep Wrangler (two-door base model, manual transmission/windows/locks) and started modifying it. First up was a turbo kit after only 10K miles (turbo sounds on the sand dunes). Previously, I had been into motorcycles (riding, maintaining, modifying), but I never had a car that I actually enjoyed until the Jeep. Then my wife and I caught the Miata disease from my brother, and we ended up buying a ’95 Miata with some suspension upgrades, roll-bar, and a turbo kit (officially, her car). After getting the Miata caught up on a lot of overdue maintenance, repairs, and cosmetic improvements, I started getting the itch for a ’90s project car of my own: the 3000GT.

Regarding electronics, my son got a Power Wheels ride-on toy when he was very young. The first time he tried it, it scared him because of the instant full power. It’s literally just a switch that connects a motor to a 12V battery. All or nothing, instant electric torque. I was into R/C cars at the time and had the idea to modify the Power Wheels so that it had proportional throttle control and used an electronic speed controller (ESC) for an R/C car.

A coworker had experience with electronics and microcontroller programming, so he helped get me started with a basic circuit and how to program microcontrollers. I programmed the microcontroller to convert a detected throttle position to the proper signal that the ESC requires to indicate desired throttle percentage. It was overall a very simple project and a great learning experience.

SM: Any particular reason why you have a 3000 GT?

Jeff: I very specifically sought a first-generation 3000GT VR4 because I was intrigued by its excessive early ’90s technology (active aero, active exhaust, active suspension, four-wheel steering, etc.), I like its pseudo-exotic styling, and, of course, its pop-up headlights. I also enjoy having a car that is unique out on the road due to its relative obscurity.

Apparently, I’m also a bit of a masochist that enjoys the thrill of finding rare parts and repairing/maintaining obscure things (evidenced by both the choice in car and the car phone project). Mine is a ’93 VR4 that is nearly completely stock (aside from minor things like tinted windows and  reupholstered seats) with all of the quirky tech/features fully intact and functioning—after I repaired several things like the active aerodynamics and the digital climate control.

SM: Is there anything else you would like to share with Hagerty’s readers?

Jeff: I hope my project inspires someone to learn something new, push the limits of their skills/knowledge, and not give up on achieving a goal. Although my Bluetooth adapter will only work with a specific model of car phone (Diamondtel Model 92), the general approach would likely work with any old car phone that has a corded handset. I’m interested to see if anyone else will build a similar kind of adapter for a different car phone.

You’ve given some of these before, but here are the links to info about the car phone project:

• GitHub repository — technical designs/explanation, diagrams, source code, basically everything you would need to reproduce my Bluetooth adapter, but it’s not a simple DIY project, though it is free for personal, non-commercial use.
• Electro-Tech-Online forum thread — full history of progress on my Bluetooth adapter.
• Information about the 3000GT factory car-phone accessory.
• My Youtube channel has many videos of my car-phone project at various stages of development, in addition to the main recent video that gives a full tour/demo of the functioning car phone system. This is more of a convenient repository for videos that I share with friends, on forums, in Facebook groups, etc. I didn’t put any effort into “appealing to the masses.” I was quite surprised when media outlets started publishing articles about my recent video.
• I recently created a TikTok account where I have been posting mostly shorter and more focused demonstrations of specific features that are maybe more appealing to short attention spans.

Have a question you’d like answered on Piston Slap? Send your queries to pistonslap@hagerty.com—give us as much detail as possible so we can help! Keep in mind this is a weekly column, so if you need an expedited answer, please tell me in your email.

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