R33 GTR Speedo

[Mobilelpg]

Hi,

I am hoping to use my Link G4+ to drive the factory speedometer in my R33 GTR and hoping someone with a more in depth knowledge of the standard speedometer/electronics can help.
As standard the Speedometer receives an AC signal from the VR sensor in the gearbox, this comes into the speedometer input pin, it then 'conditions' this signal and sends it out as a square wave to go to various other ECU's including the factory engine control unit.

What I need to specifically know is, is the actual movement of the needle done by the signal direct from the VR sensor before it is conditioned and converted to square wave, or is the needle movement based on the conditioned square wave signal?

I would like to feed the VR signal from the gearbox directly into the Link ECU as a speed input, and then send a square wave output from the ECU up to the speedometer to drive the needle.
If the needle is driven by the conditioned signal I could hopefully feed directly to that and drive the needle from the ECU, however if the needle is driven directly by the AC signal from the VR sensor then I would need to convert the Link square wave output back to an AC signal and into the speedometer input.

Hope somebody can shed some light on this.

Thanks,
Edward.

[cj]

I dont know the answer to your question about speedo needle drive, but I've got one more problem to add to your list. The VR signal from the gearbox increases voltage (and frequency) as speed increases. Assuming you work around the signal direction issues, you likely need some kind of voltage attentuator on the wire before you feed this into a DI on the link. Factory manual says the signal voltage is approx +/- 7v @ 40kph and +/- 10v @ 60 kph . Extrapolating this out, at 200kph its going to be well over the 12v you'd normally feed to a DI and might damage something if fed in un-filtered.

Is all this work just so you can do speedo correction or is there another reason?

[Adamw]

What are you trying to achieve?  I would say if the speedo is expecting an AC waveform it wont work with a square wave from an aux out.  There is possibly an external circuit you could use to convert it to a simulated AC signal but you would only do that if there was good reason to.

 

5 hours ago, cj said:

The VR signal from the gearbox increases voltage (and frequency) as speed increases. Assuming you work around the signal direction issues, you likely need some kind of voltage attentuator on the wire before you feed this into a DI on the link. Factory manual says the signal voltage is approx +/- 7v @ 40kph and +/- 10v @ 60 kph . Extrapolating this out, at 200kph its going to be well over the 12v you'd normally feed to a DI and might damage something if fed in un-filtered.

Just for your info - this wont worry the DI's.  They are designed to take VR or square wave type signals directly.  Many VR cam sensors will output upwards of 40V.

[Mobilelpg]

Hi,

Thanks for the replies and information.
I want to have accurate control of the Speedometer, currently it uses a converter chip to adjust it from KPH to MPH and this keeps dropping out intermittently.
There is a way of converting it to MPH inside the speedo head but you have to cut and bridge certain jumpers between 1 and 9 and each one of them tweaks the speed reading slightly so would involve a lot of removing the head, soldering the jumpers then road test against GPS and then adjust again and there is no real information about which jumpers control the reading by how much so could be very time consuming.
I originally thought just feed the signal to the ECU and let the ECU control the speedo, then I remembered the speedo receives the signal from a VR so I just thought if the speedo is driven by the square wave after the VR signal has been conditioned I could bypass the conditioning chip and drive it directly.
This would mean I could ditch the converter chip, make speedo adjustments easy and also, it does bug me a little that I can have RPM sweep but not Speedometer sweep.

It isn't critical as I can carry out the mods to the speedometer but really would like to use the ECU to control it.

Thanks again,
Edward.