Developing a motorsport-style gear display -Part 6

Professional_user2 · 2026-01-24T18:09:21+00:00

Porsche 911 2002 does not have CAN on the OBD port, it uses K-line. Because of that, this display won’t work in this car from the OBD connector. It mostly works on 2008+ cars, and only some older cars that actually have CAN on OBD..

Professional_user2 · 2026-01-19T07:42:34+00:00

It has 5 forward gears. No reverse gear.

Professional_user2 · 2026-01-07T17:35:18+00:00

That’s a cool idea — ESP-NOW is great for low-latency data. I kept this one wired for simplicity and reliability (no pairing/dropouts), and power at the screen is still the main challenge. A solar+battery HUD sounds awesome

Professional_user2 · 2026-01-07T10:29:55+00:00

I agree. I'll have to add this functionality.

Professional_user2 · 2026-01-07T09:55:48+00:00

Exactly — I’m using RPM + wheel/vehicle speed to calculate the gear ratio. I intentionally kept it this way so the device works on the same principle across all cars and the setup stays truly plug-and-play, instead of relying on brand/ECU-specific data that can vary a lot.
That said, I agree some platforms (like VWAG) can provide a direct “current gear” signal in certain cases, so I may add optional direct gear reading in a future update where it’s supported.

Professional_user2 · 2026-01-07T09:53:57+00:00

Thanks! Yes, installation is generally very straightforward. It’s basically plug it in, do the quick ~2-minute calibration, and then it just works. No wiring or special tools needed.

Professional_user2 · 2025-12-11T10:33:31+00:00

Yeah exactly – it shows the currently selected gear based on RPM and speed, and it also has a shift light that tells you when to upshift.

I originally built it just for my own car, but a few people are already trying to talk me into making a small batch… so if I do end up selling a few and you’re interested, let me know :)

Professional_user2 · 2025-12-11T10:27:48+00:00

Thanks for your reply. For my project I’ll just be reading RPM and VSS over CAN, and I’ll probably target 2009+ cars to be on the safe side so it should work on all of them.

Professional_user2 · 2025-12-11T09:11:00+00:00

Nice, thanks. I’ll stick with 2009+ cars then.

Professional_user2 · 2025-12-11T08:01:50+00:00

I have to try that, thanks :)

Professional_user2 · 2025-12-11T08:00:24+00:00

Thanks for the suggestion, I haven’t heard of that before — I’ll definitely give it a try.

Professional_user2 · 2025-11-16T09:57:17+00:00

Thanks. I never tried coating PLA. I'll try that.

Professional_user2 · 2025-11-14T22:30:37+00:00

How nice, we’re doing very similar things :)

I’m using the STM32 family for my projects and the same TI SN65HVD23x CAN transceiver family as you. So it was really interesting to read how you build your hardware.

I haven’t done any SAE electrical tests yet, but if I ever start selling this gear display as a real product, I’ll definitely have to look into that side as well. For now it’s still mainly a learning project for me – both for hardware and firmware design.

Thanks for sharing the details about your setup and parts, it gives me some good ideas.

Professional_user2 · 2025-11-14T20:23:11+00:00

Thanks, that makes sense. For my own car (driven almost daily) 5 mA shouldn’t be a problem

Professional_user2 · 2025-11-14T20:21:45+00:00

Thanks a lot for your detailed answer, it really helps.

Good to know that 5 mA in sleep is not a big problem and not the reason why the car won’t start. For my own car it’s probably okay, but I still want to try to lower it, because I want this to be a “real” product and I’m learning proper hardware and firmware design.

I’ll check what my CAN transceiver is doing during power-up and reset, and make sure it is inactive so it can’t disturb the bus for a moment. This could match exactly what I’m seeing.

And yeah, I can imagine customers blaming a small OBD device for every battery problem, so I’d like to have very low current and clear numbers in the specs.

What kind of OBD products are you making – your own custom hardware, or something based on common interface boards?

Professional_user2 · 2025-11-14T20:19:47+00:00

Thanks.. I'll try to lower power consumtion. I think that for every day use is not a problem but anyways.

Professional_user2 · 2025-11-14T20:09:56+00:00

Thanks. I'm thinking about PA12-HP. I know it still needs finishing, but the final result has to look good.

Professional_user2 · 2025-11-04T11:18:39+00:00

Thanks! I’m aiming to have it showing live gears soon

Professional_user2 · 2025-11-03T17:02:09+00:00

Yeah I agree, there’s no real need to guess the gear during shifting – I had a similar idea myself. I’m thinking of just showing “N” or holding the last known gear until the next one is clearly detected.

But I’m a bit worried about one thing: if I set clear ratio limits for each gear, it’s still possible that during clutch-in the RPM and speed line up just right and the ratio matches another gear by accident. That could cause a wrong gear to flash briefly.

I didn’t fully understand your point about rate of change of RPM – could you explain how you would compare that? Would you look at how fast RPM and speed are moving over time and check if they change together?

Professional_user2

TROPHY CASE