Vehicle Speed Sensor

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MegaMicra
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Vehicle Speed Sensor

Post by MegaMicra »

Hi guys. It's me, that oddball from England who's fitted the MS3X to his 55whp Japanese car.
My vss is a hall device I believe (thanks Matt) powered by 12v and goes directly into my speedo.
As I was going through my diagrams I noticed a single speed output wire that goes back to the Nissan ecu.
I scoped it out and as you can see I get a square wave that increases in frequency with speed. Unfortunately it's only 0.5v and quite noisy.


Image

Do you think if I use the 5v tps vref with a resistor it might work?
All/any comments greatly received.

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grom_e30
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Re: Vehicle Speed Sensor

Post by grom_e30 »

try connecting it to one of the ground switched inputs launch, table switch or datalog in, you prob only have a 0-0.5v working range as the stock ecu may have had a pull up in the circuit to bring the signal up to say 5 or 12v.
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

Yes, i was thinking that would be the case with the Nissan ecu pulling it up. Unfortunately my Tableswitch runs my aircon, Launch is run in as a clutch switch and my Datalog; well strangely enough is set up for exactly that lol.
I will try PT4 connection instead. Matt did mention to me that i might have to use that connection if i connected directly to it, albeit with 5v instead of the 12v it has at the mo.
At that point though i hadnt discovered this single output from behind my speedo.
What are your thoughts regarding the 5v vref as a pullup.
grom_e30
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Re: Vehicle Speed Sensor

Post by grom_e30 »

yeah tps vref with a resistor will be a ideal source as pt4 is a bit more fragile than the rest of the inputs i believe its only 5v tolerate but it can handle higher frequency's than the rest of the inputs. is your speed set up to a certain pulse per mile or is it wheel speed (x pulses per wheel rev)?
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
billr
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Re: Vehicle Speed Sensor

Post by billr »

Just be sure there is a good ground path between the stock speedo and MS. Add another ground wire there if not sure.
MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

I've not set anything up yet as I like to check I'm not going to blow anything up connecting stuff willy nilly.
I've just been looking at the MS3X card input schematics and see that PT4 has a 1k input through a diode to VCC.
Therefore I shall follow your advice and just connect it up directly and maybe it will automatically get pulled up.
Does that sound logical, or am I just talking out of my bottom?

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MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

billr wrote:Just be sure there is a good ground path between the stock speedo and MS. Add another ground wire there if not sure.
OK I'll check this out thank you.

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MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

Right I've checked that the instrument cluster has a good gnd, and also noted that the VSS is grounded to all the other sensors, cam, coolant etc so by default it's already connected to my Megasquirt sensor gnd. Should be good to go then.

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MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

grom_e30 wrote:yeah tps vref with a resistor will be a ideal source as pt4 is a bit more fragile than the rest of the inputs i believe its only 5v tolerate but it can handle higher frequency's than the rest of the inputs. is your speed set up to a certain pulse per mile or is it wheel speed (x pulses per wheel rev)?
With regards the speed setup; the VSS is the oem one attached to the gearbox so I'm assuming it's going to be pulses per mile. My car is super simple and doesn't have wheel speed sensors for ABS or the likes. It was just designed for getting grandma's around and delivering pizzas haha.

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MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

So to test this out further I've added a 12v pull up via a 2k resistor to the signal from the speedo.
This has cleaned up the signal and made it usable. I will be using 5v as the pull up obviously, but it's easy to grab 12v for testing. The frequency output is half the speed reading shown on the speedo.

Image

As soon as I get some free time I'll get it wired up.
Once again, thanks for all your help and input guys.

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MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

So as the weather is atrocious, and I have no garage or cover I was just going through the schematics of the MS3X inputs along with my VSS data I collected the other day.
The frequency is not very high and is only in ever going to be in the 10s of hertz. For example 20mph is 10hz, 30mph is 15 etc it's exactly half. Do you think I could use the Nitrous in connection and use the jp8 jumper to pull it up to 12v.

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whittlebeast
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Re: Vehicle Speed Sensor

Post by whittlebeast »

What is that scope?
grom_e30
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Re: Vehicle Speed Sensor

Post by grom_e30 »

MegaMicra wrote:So as the weather is atrocious, and I have no garage or cover I was just going through the schematics of the MS3X inputs along with my VSS data I collected the other day.
The frequency is not very high and is only in ever going to be in the 10s of hertz. For example 20mph is 10hz, 30mph is 15 etc it's exactly half. Do you think I could use the Nitrous in connection and use the jp8 jumper to pull it up to 12v.

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give it a try if you find the speedometer in ms drops out at higher speed then you may need to use pt4 instead
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

whittlebeast wrote:What is that scope?
It is DSO203. I've borrowed it off a friend. They're about £100 I believe. I've found it useful due to the size.

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MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

grom_e30 wrote:
MegaMicra wrote:So as the weather is atrocious, and I have no garage or cover I was just going through the schematics of the MS3X inputs along with my VSS data I collected the other day.
The frequency is not very high and is only in ever going to be in the 10s of hertz. For example 20mph is 10hz, 30mph is 15 etc it's exactly half. Do you think I could use the Nitrous in connection and use the jp8 jumper to pull it up to 12v.

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give it a try if you find the speedometer in ms drops out at higher speed then you may need to use pt4 instead
Ah right I see. OK. Nothing ventured eh, as they say. Thanks.

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MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

OK, so I ended up connecting the VSS input to the launch in connection as it was the easiest to get to. And let's be honest, do I really need launch control lol, it's 55whp for goodness sake.
As the frequency is exactly half of the speed shown on the dash I just multiplied 30hz X 60mph which gives 1800pulses /mile.
Job done. It all works flawlessly, I'm so pleased. I've typed in all my gear ratios also and final drive so that it now shows what gear I'm in. As my 4th and 5th ratios are really similar it has a hard time recognising 5th if I'm quick on the gear change. I'll probably cheat and alter the ratio very slightly. It really is a good piece of kit this Megasquirt isn't it.

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MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

Oh, nearly forgot in all my excitement.
Thanks to @grom_e30 and all you other guys for helping me out.

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grom_e30
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Re: Vehicle Speed Sensor

Post by grom_e30 »

do I really need launch control lol
there is always 'speed based launch control' that you could have a play about with
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
MegaMicra
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Re: Vehicle Speed Sensor

Post by MegaMicra »

Well, as usual I can't stop messing and as I'm a bit ocd I've disconnected my VSS input from the launch in wire and connected it via a 1k resistor from the 5v tps connection to PT4 input.
Appears to work perfectly so I've got my launch wire back. Thought I might as well post what I've done incase anyone searches for howtos.

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genericusername
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Re: Vehicle Speed Sensor

Post by genericusername »

Are you still using a hall sensor or did you switch to a VR type sensor?
I'm having an issue where i'm using a VR sensor (stock one from my GM t56 trans), and the vehicle speed gauge is all over the place, so i'm assuming it's all noise. I'm going directly into PT4+ and PT4- on my MS3 gold box with the VR sensor like the manual says, but perhaps i need a resistor too?
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