GPS performance meter on in-car PC

Timmy C · 06-05-2005, 12:56 PM

Hi there, great site youve got here.

Im planning to build my own incar PC, ive got most of it straight in my head but im struggeling on how to add the function of a performance meter to my system for- 0-60 timing, 30-50 timing etc, Quartre mile timing, force and power estimations and so on.

Will i need a GPS reciever with a higher than standard sample rate?
Is there any software currently available for this. If not what do i do as i only have limited programming skills.

I have also been considering linking the system to the cars ECU for live mapping. I would consider upgrading my ECU for this, has anyone had any experience with this and does anyone know of any copmataible aftermarket ECUs
Another option is connecting the system to the cars air, temp, oil sensors like data logging systems currently avaiblable, does anyone know how this could be done on the go.

I also have one or two other questions.
My car-Pc will be based on a laptop which has a pretty poor sound card. Are there any external sound cards available with phono line outs so that i can connect to my current amplifiers.

Any suggestions for other software would be greatly appreciated, like a good sat nav program with gps locations of speed cameras.

Seen as ive asked somany questions i will describe what i plan to do incase you are interested.

The laptop will be hidden in the dash and its power button will be linked to the ignition so that it comes on when the car is started with a manual overide of course.

The system will mainly be controlled by an 8" touch screen LCD built into the dash but the laptops own screen will disconnected from the laptop and hidden in the passenger side of the dash.

To the laptop i will add:

A wi-fi pcmcia card to allow remote access updates and transfers from my home pc

A GPS reciever for nav, speed cam detection, performance meter

DAB radio reciver

High quality external sound card

Blue tooth dongle for hands free mobile phone functions

Usb hub built in to the dash for any other connections

The side of the laptop will be flush with the dash so the dvd player is accesible. As i already have the laptop lieing arround costs ontop of its value are estimated at £260 which seems fair considering all the functions.

evandude · 06-05-2005, 01:14 PM

I don't think GPS will work for your purposes. GPS updates too slowly for any kind of precision timing or anything, and it's also not really accurate enough for that stuff. if you want force and power estimations, use an accelerometer. if you want truly accurate 0-60 times and such, add a high-resolution speed sensor to your drivetrain somehow, or tap into the speedo signal if you don't need as high a resolution. either one is going to require a bunch of hardware and software to be made though.

The easy thing to do would be to just buy one of the available devices that does all that stuff, they're a few hundred bucks but it'll save you a lot of effort...

Timmy C · 06-05-2005, 06:10 PM

There are stand alone GPS performance meters on the market based on GPS recivers with 200 samples per second. I f i were able to get a PC GPS reciver with that smaple rate then it would be accurate enough but it would only be worth it if there was software about for what i am trying to do.

0l33l · 06-05-2005, 06:22 PM

Quote: Originally Posted by evandude

I don't think GPS will work for your purposes. GPS updates too slowly for any kind of precision timing or anything, and it's also not really accurate enough for that stuff. if you want force and power estimations, use an accelerometer. if you want truly accurate 0-60 times and such, add a high-resolution speed sensor to your drivetrain somehow, or tap into the speedo signal if you don't need as high a resolution. either one is going to require a bunch of hardware and software to be made though.

The easy thing to do would be to just buy one of the available devices that does all that stuff, they're a few hundred bucks but it'll save you a lot of effort...

Ummm... http://www.pistonheads.com/ultima/default.asp?i=9208

Scouse Monkey · 06-05-2005, 06:27 PM

Quote: Originally Posted by 0l33l

Ummm... http://www.pistonheads.com/ultima/default.asp?i=9208

oooo I hve been past that airfied a few times (recognise the 747)

I have seen GPs modules that can run up to 8hz from U-blox but to be hoest an intertial system would be better.

0l33l · 06-05-2005, 06:32 PM

Quote: Originally Posted by Scouse Monkey

oooo I hve been past that airfied a few times (recognise the 747)

I have seen GPs modules that can run up to 8hz from U-blox but to be hoest an intertial system would be better.

Well, what we care about is that its possible. Now someone needs to figure out how

Scouse Monkey · 06-05-2005, 06:44 PM

you can do it like the U-blox Dr system works by using the VSS speedo pulses calibrated by GPS.

I.e you monitor the VSS pulses and compare them to the GPS to get calibration for the current car and tyre size, pressure etc etc. Then you use this data to calculate the 0-60 time. This works much faster than GPS can. The u-blox with this feature can only output to the serial port at 1Hz but the DR part worksa t about 40hz.

Or you can use a 2 DoF accelerometer system to work out the accelerations and thus integrate them to get the speed and distance covered and laterial loads.

Timmy C · 06-06-2005, 05:35 AM

Are accelerometers actually that accurate? I cant see how a system based on a mass on the end of a spring can be that good!

If so are there any accelerometers that could be interfaced with a car pc and give live performance data?

0l33l · 06-06-2005, 05:39 AM

http://www.sparkfun.com/shop/index.p...266326&cat=71&

Scouse Monkey · 06-06-2005, 06:09 AM

Quote: Originally Posted by Timmy C

Are accelerometers actually that accurate? I cant see how a system based on a mass on the end of a spring can be that good!

If so are there any accelerometers that could be interfaced with a car pc and give live performance data?

ROFL! how do you think missiles and jet planes navigate?

GPS?

Inertial systems can be incredibly accurate and fast. Look at the speed of missiles and what if you loose the GPS signal? Aircraft NEVER use GPS as their main for of navigation - it is too risky.

Timmy C · 06-06-2005, 09:28 AM

Quote: Originally Posted by Scouse Monkey

ROFL! how do you think missiles and jet planes navigate?

GPS?

Inertial systems can be incredibly accurate and fast. Look at the speed of missiles and what if you loose the GPS signal? Aircraft NEVER use GPS as their main for of navigation - it is too risky.

Fair enough.

0l33l · 06-06-2005, 10:44 PM

Quote: Originally Posted by Scouse Monkey

Inertial systems can be incredibly accurate and fast. Look at the speed of missiles and what if you loose the GPS signal? Aircraft NEVER use GPS as their main for of navigation - it is too risky.

Yeh... what if the russians put a mask over the sky that would block GPS signals?

Timmy C · 06-07-2005, 12:36 PM

Surley planes cant navigate by measuring inertia. Lets say the acelerometer was accurate to 0.001 m/s2 which is extreamly accurate! Then your position would be accurate to 0.001 m in the first second of flight. But the inacuracy would compound every second so after 2 seconds your to +/- 0.002m so by the end of a long 30 hour filght your over 100 meters off in every direction which would cause serious trouble for automated landing!!

With GPS your position is re checked regularly so your inacuracies do not compound. If a plane did loose its GPS system i cant see how it could posibly fly on acelerometers alone!!

Anyway were not talking about planes. Normal GPS navigators in your car claim to work out your velocity to 0.1 mph which is acurate enough for me, just need a higher sample rate and some nice software for the job.

IntellaWorks · 06-07-2005, 12:45 PM

http://www.phidgets.com/index.php?mo...32.9.61&IID=92 http://www.phidgets.com/index.php?mo...32.9.61&IID=92

Scouse Monkey · 06-07-2005, 01:10 PM

Quote: Originally Posted by Timmy C

Surley planes cant navigate by measuring inertia. Lets say the acelerometer was accurate to 0.001 m/s2 which is extreamly accurate! Then your position would be accurate to 0.001 m in the first second of flight. But the inacuracy would compound every second so after 2 seconds your to +/- 0.002m so by the end of a long 30 hour filght your over 100 meters off in every direction which would cause serious trouble for automated landing!!

With GPS your position is re checked regularly so your inacuracies do not compound. If a plane did loose its GPS system i cant see how it could posibly fly on acelerometers alone!!

Anyway were not talking about planes. Normal GPS navigators in your car claim to work out your velocity to 0.1 mph which is acurate enough for me, just need a higher sample rate and some nice software for the job.

GRRRRRR GPS is relatively new! Inertial systems are pretty accurate if done right and are a lot faster than GPS.

How do you think the rockets that put the GPS satellites in orbit got to the right spot? INERTIAL NAVIGATION!

Gyros and accelerometers are very accurate but yes any error int he system is compounded by cumulative errors.

Airliners have to sit on the runway while the inertial system is calibrated. There was a Korean 747 that was moved too soon and ment massively off course. It ended up over Russia by mistake and the captain was too proud to admit his mistake and identify himself. The place with a few hundred people onboard got shot down.

GPS can never be relied on for navigation as it relies on external equipment beyond the control of the other 192 countries that may use it. And that is before you have to worry about failures and bad weather.

GPS could never cope with the update speeds required for missiles, rockets and fighter aircraft and when a spacecraft is out in the edges of the solar system how on Earth is it going to get a signal from a geostationary GPS satellite?