Unused Racing/Rally Wheel Expansion Port

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Moopthehedgehog
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Unused Racing/Rally Wheel Expansion Port

Post by Moopthehedgehog » Sun Oct 27, 2019 10:47 am

Hello! Time sure flies, huh?

Got a question that I was hoping someone here might know the answer to. I was taking apart an official Dreamcast steering wheel earlier this week to make some modifications (add rumble and tap the triggers for pedals) and saw that the unused 5-pin mini-DIN expansion port on it is connected directly to the E2 Maple chip. As far as I could research, the port is meant for pedals that were never made and was ultimately removed from the wheels sold in Europe (but the 5-pin internal connector is supposedly still there on the PCB). It doesn't look like it's wired up for simple analog pedals that merely contain potentiometers like other wheels of the era--it looks like a dedicated daisy-chain controller port or something of that sort.

Does anyone know how that might have worked? I have not been able to find any documentation on it.
I'm kind of tempted to slice up a controller extension cable to see what happens if I plug in a standard controller...
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Re: Unused Racing/Rally Wheel Expansion Port

Post by |darc| » Wed Oct 30, 2019 7:13 pm

Could it be the same as those used on 3rd party wheels? I have an InterAct Concept 4 Racing Wheel and it has pedals. They connect through a 6-pin mini DIN though.
It's thinking...
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Re: Unused Racing/Rally Wheel Expansion Port

Post by Moopthehedgehog » Thu Oct 31, 2019 10:23 am

It definitely looks like it’s meant for pedals, yeah. The weird part about it is that it’s not a simple analog passthrough like what I think all of the 3rd party wheels use. It instead appears to be daisy chained as a distinct controller, meaning that connecting the nonexistent “official” pedals would have been like plugging in a Dreamcast controller into another Dreamcast controller plugged into the console. I haven’t come across any other peripheral that would have done this, and the maple bus documentation that I can find only mentions that daisy-chaining is possible.

Technically, you really only need 4 or 5 pins for pedals: usually either 3.3V or 5V (sometimes separated per pedal), analog voltage output per pedal, and common ground, and that’s what I think the Interacts and Mad Catz ones use (maybe a 6-pin separates the grounds). The official wheel’s 5-pin connector, however, is electrically more like a 5-pin controller port on the front of the console itself. That’s what’s weird about it, and I can’t find any specific info about how that would’ve worked.

Something like this may allow enterprising homebrew developers to make new kinds of peripherals, as it would mean that maple is basically just a variant of (or early competitor to) USB.
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