My car's speed - measuring - reading

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atferrari

Well-Known Member
Wondering what could be the simplest way to implement a basic sensor to measure my cars' speed wrt ground, every 5 sec or so for a period of 1 or 2 hours time? Not precise but consistent.

Additional log implemented in a RAM with automatic time stamping plus eventual "bookmarks" at the push of a button.

No display but reading when at home just to evaluate my driving performance

Power supply, a 9V battery (by no means associated to the car's common). Tapping into the car's wiring (whatever it is) is not considered.

JimB

Super Moderator
Put some kind of a slotted disc on one of the drive shafts and count the pulses, either magnetically or optically.

JimB

jpanhalt

Well-Known Member
Does your car have ABS? If so, you already have the signal you need. The pinouts are available for most modern cars, but getting the dealer manual can be expensive if bought new.
1) A friendly dealer may just give you that information for good will.
2) I have bought the manuals for my vehicles on ebay (Cleveland is near Detroit) for mere pennies on the dollar.

John

ronsimpson

Well-Known Member
In the US there is a computer port on cars. The insurance company has a data logger that plugs in and "records your speed". My insurance will drop in price if I let them record for a month. (Maybe the price will increase, the way I drive) I do not know if they can really see my speed through the computer port.

On my older cars I can only get "error codes". On the new cars they say you can get graphs of many things over time.

Diver300

Well-Known Member
A GPS logger is the simplest way to do it. Most vehicle tracking units will do what you want, and upload the data while driving.

dr pepper

Well-Known Member
Most vehicles have a Vss vehicle speed sensor mounted on the gearbox, and usually they are 4 ppr, you could tap into this.
Another more involved way is to use the cars Obd port, if its later than 2001 that is, vehcile speed is one of the pid's you can pull from the port.
If your into arduino there is a open source project OBDuino, you could use this to talk to the car, I've messed with it a couple of times its not hard to do, you can get an interface an ELM327, there are wired Rs232 and wireless blutooth versions, you can get them cheap on ebay, they do all the fancy comms stuff for you, you just 'talk' to the vehicle's Ecu using serial via the ELM, just send a mode, then send a Pid code and the car will reply with the data.

jpanhalt

Well-Known Member
I wonder the ultimate aim. I recently changed from the OEM tires (Michelin) because the originals became very checked after 2 years and after 4 years wouldn't hold air. Gas mileage on the dashboard indicator went down after the change. Was that because the actual mileage was the same, but the indicate miles driven was different because of the tire's diametrical difference?

I wish I had GPS at the time to compare actual trip distances.

John

dr pepper

Well-Known Member
I think the extra grip of new tyres would have had some effect in the reduction in mileage Jp.
Did the garage put the correct pressure in the new tyres?, that makes a difference.

jpanhalt

Well-Known Member
My tires are always at the correct pressure, except the Michilin's. I let one go low and went to the local Ford dealer for a recall. I got the "free" safety multi-point check with a nice little sheet showing everything that was checked OK. That included tire pressure. The tire I knew was low (about 10 PSI) was determined by the dealer to be at the correct pressure. Even for a radial tire, you could see it was low. I checked at home, it was low, as expected. The dealer not only didn't check, he didn't bother to add air. Dealer lost a customer.

Well-Known Member
I had an app on my last smart phone which using GPS would indicate speed. Thus a GPS module with the right data out could likely work. While I don't know about Argentina here in the US cars have a computer diagnostic port commonly called an OBD II port allowing for diagnostics. A laptop running any good terminal emulation software like Microsoft Hyper Terminal or Terra Term will communicate with the OBD system. Using a laptop or micro-controller you could log the data for several parameters like speed, engine RPM, temperatures and other things. OBD Solutions READING REAL-TIME DATA is a good read on the subject. You will need a RS232 to OBD interface cable but it could likely work. A Google of "RS232 to OBD interface cable" will get you dozens of build or buy solutions. The collected data could easily be saved on the fly.

Ron

ClydeCrashKop

Well-Known Member
This is probably more than you want but your question reminded me.
Nuts and Volts magazine has a Near Space column about sending balloons as high as they will go with sensors and test equipment. In the March 2007 issue they collected GPS data throughout the flight path with a Tiny Trak 3, and then displayed it in 3-D on Google Earth. A Tiny Trak 3 is essentially a one-way radio modem that you can purchase online at www.byonics.com.
Now it’s time to add the coordinates of the balloon’s path. There’s only one coordinate per line of text and each coordinate is a point in three-dimensional space with the following format: longitude, latitude, altitude.
You’ll get a three-dimensional feel for the flight path as you move around it with the controls.
http://nutsvolts.texterity.com/nutsvolts/200703?pg=16#pg16
There’s a short KML tutorial at https://developers.google.com/kml/documentation/kml_tut
and more complete tutorials at https://developers.google.com/kml/documentation/kml_21tutorial

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dr pepper

Well-Known Member
Never heard a story like that usually when you get a 'free' check or cheap Mot it means you get a long list of jobs that dont need doing, my Mot inspector was telling me just the other week that he's had cars in that have been to a well known chain of garages and failed with a long list of faults, none of which warranted a fail, and went on to tell me its so bad the government has changed the rules so that parts have to be nearly falling off before it fails to try and prevent this kind of unnecessary work.
I'd have a hard time telling a customer they neede this that & t'other when they didnt, maybe I'm a fool.
These days I'm not surprised your tyres were not checked.

jpanhalt

Well-Known Member
Credibility is lost in an instant and never regained. Small town (actually a village in America). Its loss.

Well-Known Member
My tires are always at the correct pressure, except the Michilin's. I let one go low and went to the local Ford dealer for a recall. I got the "free" safety multi-point check with a nice little sheet showing everything that was checked OK. That included tire pressure. The tire I knew was low (about 10 PSI) was determined by the dealer to be at the correct pressure. Even for a radial tire, you could see it was low. I checked at home, it was low, as expected. The dealer not only didn't check, he didn't bother to add air. Dealer lost a customer.
Thanks for the reminder, I have a low tire on my truck. Went to the drug store yesterday and the display told me. Since I retired I can fill the tank and a few months later it is still full. The on board computer monitors tire pressure and is kind enough to let you know if a tire is low or not sensing data.

Also, what happened there is totally unacceptable.

Ron

jbeng

Member
atferrari - you could see if you could get your hands on a used speed radar, that would be consistent and precise.

Reloadron - your onboard computer monitoring the tire pressure reminds me of when I rented a car for vacation last year. About 350 miles into a 1000 mile trip, the computer showed a tire with low pressure. I stopped and added air to the tire which it indicated, but the fault kept showing. One would think that it would be obvious which was the offending tire, as it would visually appear low, but this wasn't the case as it was only a few psi low (like 5). I topped off all the tires & the fault cleared. Turns out the tires had been rotated, but the sensors hadn't been reset, so the fault was being reported on the wrong tire. (It was a 2016 Chevy Cruze, btw.)

Well-Known Member
atferrari - you could see if you could get your hands on a used speed radar, that would be consistent and precise.

Reloadron - your onboard computer monitoring the tire pressure reminds me of when I rented a car for vacation last year. About 350 miles into a 1000 mile trip, the computer showed a tire with low pressure. I stopped and added air to the tire which it indicated, but the fault kept showing. One would think that it would be obvious which was the offending tire, as it would visually appear low, but this wasn't the case as it was only a few psi low (like 5). I topped off all the tires & the fault cleared. Turns out the tires had been rotated, but the sensors hadn't been reset, so the fault was being reported on the wrong tire. (It was a 2016 Chevy Cruze, btw.)
I never gave that much thought. Yeah, each tire has a code in the pressure transmitter so if I were to take the LR and move it to and move it to LF the sensor would indicate Check LR when in fact it would not be.

Ron

audioguru

Well-Known Member
I have never had a car that was powerful enough to do a wheelie or a burn out. So I look at the accurate speedometer and don't bother to measure the actual ground speed.

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dr pepper

Well-Known Member
Tps (tyre pressure sensors) can be a right pain and expensive, to change a transmitter you need to recode the transmitter, and some have a lithium battery to run out.

Well-Known Member
Yeah and good shops have to buy the tools to read and program those things. I have one that is flaky and when I had the shop I like look at it figures the thing worked just fine. Every now and then it throws and error but I am not going to worry about it. I have seen the tools for $30 to$139 on Amazon. I do have an OBTII reading device which is fun to play with. I used it to reset my old truck. That thing has come in handy on a few occasions.