GPS Speedo Adaptor

[whrdnsx]

Anyone know if any GPS speedo adaptors will work with the NSX speedo?

maybe something like this;
http://vpw.com.au/Category/Index/27085
http://www.summitracing.com/int/parts/izl-s9020/overview/
Thanks

 

[sparky]

While GPS is highly accurate at steady speeds it is very slow to respond to speed changes (compared to a needle). So not fast enough to quickly check actual speed when you spot the cop car and wonder what the last speed limit sign said, combined with absurdly tight Aussie speed tolerance !

I've not looked into these item in detail, but would be surprised if they have found a way around this issue. Unless they somehow do some clever data fusion with the speedo signal, for best of both worlds? If that's the case I'm interested too ...

As a side issue : as the global car companies became aware of those absurdly tight Aussie speed tolerances, most decided to make speedo's read a 3-5 kph high so they won't end up in court being sued by someone for speeding fines due to a slightly inaccurate speedo. The net result is many/most drivers sitting on or just below 60kph by their speedo are actually doing 55... leading to a completely false sense of safety as cars form large flocks traveling at identical (slow) speeds, leading to obvious traffic build up and driver frustration as more and more people go slower and slower ... how dumb is that!?

 

[Old Guy]

I am thinking it will not be plug and play! Even though the Autometer GPS unit has a user adjustable calibration for the pulse count, the manual refers to an industry standard 12v pulse output. The NSX service manual refers to a 5 volt pulse out of the speed sensor. You can probably make it work if you are prepared to fabricate an interposing circuit.

With respect to Sparky's comments - perhaps GPS satellite coverage is not so great in the Antipodes or your GPS unit is a bit antiquated. I have a Speedhut GPS speedometer with a stepper motor driving an analog gauge. Update time is absolutely not a problem with the Speedhut unit. You will have to find another excuse for speeding tickets. The only time things get iffy is in multi story parking garages with lots of rebar. If you are close to an open part of the structure it will usually have a shot at sufficient satellites to do a capture. My speedometer has a hot start feature so that it usually has capture within 5 -10 seconds at the most following start up.

On the side issue - vehicle manufactures have been fabricating erroneous speedometers for years and definitely predates global spec cars. The only thing is that they insure that they err on the side of reading high. As you note, it reduces the risk that unhappy customers may seek redress for collecting speeding tickets.

 

[sparky]

Even with great GPS coverage conventional GPS can never be as fast as hard wired speedo - for two reasons:

Firstly it has to take multiple position readings to calculate speed and then average them. Even if GPS takes a reading 5 times a second averaging takes time - typically a second or two.

Secondly GPS position data is only accurate to a few meters so this adds errors to speed unless averaged over a lot of readings and a longer time period (that's why accurate readings are only available when staying at steady speed for about 10 seconds).

By comparision a hard wired speedo is getting hundreds of pulses a seond so it can react to changes in a fraction of a second.

So unless the GPS is supplemented by another sensor system it's calculated / displayed speed will lag actual speed by typically 1, 2 or more seconds. I find that is enough that I can't trust it whenever I'm changing speed. But i trust it entirely for calibrating my speedo - at steady speeds.

Having said all that, I do hope there is a product available that solves this problem, a speedo that is accurate (and responsive) across tyre size changes would be great!

 

[whrdnsx]

Thanks for the replies.
I'm not too concerned if its not super fast or accurate. Just want to make sure it will work before I spend the money.

 

[sparky]

here's an Aussie website that has a good range: gpsspeed

 

[warrenw]

I am in Canada, (kms/hr) and my car is from the US (miles/hr) With speed limits in kms/hr, I need a quick kms/hr reference. The speedometer in the car is hard to read the kms/hr. I use a PassPort 9500ix radar detector, and have it defaulted to display my speed in kms/hr when not detecting radar. I can convert in my head very well, and fast, but this is just a backup. It works pretty well, but it is definitely slower than my speedo in the dash.
https://www.escortradar.com/passport9500ix/
it also has a great database with all the speed on green and red light cameras for NA.

Something else to add: if you disconnect the speed sensor from the transmission, you will get a check engine light.

 

[Old Guy]

I am in Canada, (kms/hr) and my car is from the US (miles/hr) With speed limits in kms/hr, I need a quick kms/hr reference. The speedometer in the car is hard to read the kms/hr. I use a PassPort 9500ix radar detector, and have it defaulted to display my speed in kms/hr when not detecting radar. I can convert in my head very well, and fast, but this is just a backup. It works pretty well, but it is definitely slower than my speedo in the dash.
https://www.escortradar.com/passport9500ix/
it also has a great database with all the speed on green and red light cameras for NA.

Something else to add: if you disconnect the speed sensor from the transmission, you will get a check engine light.

I can relate to that. On a couple of occasions after I got my car, while accelerating on lightly travelled sections of road I had a oops, that's not 100 kph moment!

Correct about the MIL light coming on. Just for good measure, the speed sensor also ties into the cruise control on early cars, the electric power steering and the controller for auto transmission cars. However, if you get the GPS pulse width, rate and voltage to match the Honda speed sensor, everything should work. One thing I have never figured out is why Honda continued to use a separate speed sensor when they already had 4 speed sensors on the wheels for the ABS. Perhaps they were legacy systems adopted from other Honda products.

 

[Kaz-kzukNA1]

..........One thing I have never figured out is why Honda continued to use a separate speed sensor when they already had 4 speed sensors on the wheels for the ABS. Perhaps they were legacy systems adopted from other Honda products.

It’s the requirement based on JIS.
I wrote this somewhere on here in the past and apology to the OP for going off-topic but even with the same tyre size spec on the sidewall, the actual circumference is different depending on the tyre manufacture, tyre pressure, etc.
Therefore, it will cause different reading on the speedo depending on many factors.

In order to eliminate the deviation, the VSS pulse is defined in the JIS and it’s based on the frequency (number of rotation) of the VSS itself and not the tyre rotation.

For 4 wheels car, the VSS must be at 637rpm at 60kph.
The number of pulse generated by one rotation of VSS must be 4, 8, 16, 20 or 25.
Honda uses 4 pulses per VSS rotation and this is not per tyre rotation.

JIS defines that the input signal frequency to the speedo must meet the following equation.

H[Hz] = V[kph] x n[pulse per VSS rotation] x 637[rpm] / 60[sec] / 60[kph]

So, all Japanese car manufactures are required to meet this regulation and thus, NSX has dedicated VSS addition to the four wheel speed sensors.

Kaz

 

[Old Guy]

An interesting regulatory requirement. I am sure there is probably some historical basis for this requirement, although it strikes me as a very application specific method of meeting what is presumably a performance regulation. The JIS mandates a standardized response rate by the Speedometer. Does the JIS also mandate that the VSS must be 4, 8, 16, 20 or 25 pulses per rotation? That would preclude using an ABS wheel sensor directly as an speed sensor. Sounds like an issue of legacy regulation rather than legacy systems!

With a relatively simple digital circuit you could take the ABS wheel sensor signal and create a signal that would be compatible with the JIS requirement for the speedometer response. It would be possible to make the adjust the calibration of this pulse counter circuit to correct for tire and wheel size changes. Of course, you should also be able to do the same with the VSS output which would allow you to correct the pulse rate for changes in wheel and tire size.

Edit

How about that, somebody beat me to the market!

http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=126/prd126.htm


Just a heads up, because of the connection to the auto transmission controller, its probably best to not use a GPS input or pulse count adjustment for the speedometer input. If the transmission controller uses engine speed and the VSS to assess slip, you could really mess the transmission up.