Rovergauge Cable

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3VILC
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Rovergauge Cable

Postby 3VILC » Fri Jun 15, 2018 10:38 pm

Has anybody got/made a rovergauge cable recently? It would seem to be an extremely useful tool for a rover v8 but the recommended usb cable to use are still over 50bux delivered. Wondering if the much more cheaply available ftdi usb-serial converters intended for programming ardueno (sp? ) style boards would work? They seem to be essentially the same thing just a bare board rather than a nice cable
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Re: Rovergauge Cable

Postby phaedrus » Sat Jun 23, 2018 7:37 pm

Yep, the FTDI interface will work, and the connection detail is available on Github IIRC.

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Re: Rovergauge Cable

Postby 3VILC » Fri Jul 06, 2018 9:06 pm

That said, it turns out not too surprisingly the cheap boards on trademe are fake FTDI chips.. for normal purposes this is probably fine, but since we need to configure them to read an inverted RX line, they are no good as of course the fake chips are write protected so changing the config is not possible :/ I do have an old BMW CANBus cable which is FTDI based so I might try and bypass the CAN chip and see if I can get a signal directly into the FTDI chip..assuming of course this isnt a fake chip but this was a $50 adapter not a $10 board so fingers crossed
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Re: Rovergauge Cable

Postby phaedrus » Sat Jul 07, 2018 9:25 pm

It's been a while since I looked at this but if you found the FTDI board wouldn't config as needed I suppose I'd just invert the line using a bit of hardware - even a transistor would probably do.

Sorry I can't comment on the Trademe boards, I've never bought any of those.

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Re: Rovergauge Cable

Postby 3VILC » Sat Jul 07, 2018 10:33 pm

yes couldnt configure for inverted RX or change any settings as the chip is read only. i suppose I could hardware invert it, but its been a while too and I'm lazy these days haha. For a $6 board I'm not suprised to be honest. I tried asking Jaycar if their boards are genuine at $30 I would expect them to be but no reply.
I have an old BMW cable that I'm fiddling around with now trying to work out if its a genuine chip in that. By the looks of the data sheets you can input serial signals direct into the chip (obviously with the external resistor to pull the 12v lucas signal down to 5v-ish..not that trying to solder something to the tiny pins of a surface mount chip looks particularly fun either haha
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Re: Rovergauge Cable

Postby 3VILC » Sat Jul 07, 2018 10:56 pm

On that note, after a bit of playing around it appears the chip is indeed genuine, had to force install the drivers every time, turns out it was set to a custom VID/PID to restrict it to the original 'BMWScanner' driver, but successfully reprogrammed the chip back to the standard FTDI settings along with inverted RX, unplugged and replugged now the default FTDI drivers install automatically and the setting stick, so thats promising.. now just to work out how the heck to try solder some wires directly to the TX/RX pins :) And hopefully the CANBus encoder chip doesnt mess with it. Cant see any other easy point to directly connect some wires..unless i use the TX/RX side of the CAN chip and assume its directly connected to the opposite pin on the FTDI and risk damaging the chip we dont need first
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Re: Rovergauge Cable

Postby Alister » Mon Jul 09, 2018 2:51 pm

FWIW, I believe the cable I bought was this one: https://nicegear.nz/product/ftdi-cable-5v
Worked without any issues if I'm remembering correctly.

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Re: Rovergauge Cable

Postby phaedrus » Mon Jul 09, 2018 7:37 pm

Had's (Nicegear) lead should be fine, as should most any other serial-usb interface.

Inverting the signal is straightforward - just use an NPN transistor such as a BC549 with emitter to ground, collector to the RXD line (of the interface) and feed the base from the 14CUX via a resistive divider (well, I'd use a divider, you may get away with simply feeding it directly with say a 2k2 resistor [or thereabouts]).

Depending upon the interface you may need a pullup resistor on the collector. Of course you could also use a FET or any number of IC's, I suggest the BC549 etc 'cos almost anyone will have one - or I expect you could pull it's equivalent out of various old boards...

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Re: Rovergauge Cable

Postby 3VILC » Tue Jul 10, 2018 12:13 am

Thanks for that phaedrus exactly the info I was looking for. I knew it was a fairly simple fix (looking at how they describe how the signal ends up inverted inside the 14CUX and thinking surely I could just do something similar to invert it back again). Might have to break out the breadboard and have a fiddle. Gives me something to do. It's been a while since I've tinkered that far. So if I'm correct I could voltage divide it, or put a resistor in series, or use a 400ish ohm pull down as per the original cable instructions? it's obviously not too fussy.
In actual fact doing more reading I've confused myself more now, the original cable plans simple specify a 400 ohm resistor between RX and ground and I can't quite work out how that is meant to drop the voltage down to 5V. Clearly it works if that's how everyone's done it

Note kids: just buy the right cable first time around haha.
phaedrus wrote:Had's (Nicegear) lead should be fine, as should most any other serial-usb interface.

Inverting the signal is straightforward - just use an NPN transistor such as a BC549 with emitter to ground, collector to the RXD line (of the interface) and feed the base from the 14CUX via a resistive divider (well, I'd use a divider, you may get away with simply feeding it directly with say a 2k2 resistor [or thereabouts]).

Depending upon the interface you may need a pullup resistor on the collector. Of course you could also use a FET or any number of IC's, I suggest the BC549 etc 'cos almost anyone will have one - or I expect you could pull it's equivalent out of various old boards...
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Re: Rovergauge Cable

Postby phaedrus » Tue Jul 10, 2018 9:06 pm

If you're going to connect directly to the FTDI input then yes, just put a 390 ohm or thereabouts to ground at this point.

If you look at the data output schematic of the 14CUX it is fed from 12v via a 500 ohm to the transistor collector, then a 100 ohm resistor out. Putting a 390 to ground will mean this series of resistors will act as a voltage divider and reduce the input voltage to a suitable level for the ttl FTDI where the 100 and 390 ohm resistors connect.

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Re: Rovergauge Cable

Postby 3VILC » Thu Jul 12, 2018 2:53 pm

Many thanks to phaedrus this simple trick worked. Cable now works just fine. FyI this was the cheapest of cheap $5 ftdi interfaces and it works just fine for this purpose with a couple of components from the junk pile.
Confirmed what I already knew no output from afm. New afm fitted and working. Now it won't idle haha. Idle was always a bit oddball with the stuffed afm but it never got close to stalling. Although I suspect as someone had fiddled with the mixture screw on the afm then they have possibly also adjusted base idle screw or tps trying to get it to run right. Tps shows 5% at idle however so that seems to be in range.
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