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Mikemeakin
Just joined
Username: Mikemeakin
Post Number: 1
Registered: 04-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, 18 April, 2006 - 10:36 pm: | 
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Been thinking about making a vehicle speed warning device for my car similar to the device found at www.speedguard.co.uk . This takes the 'speed' signal from the vehicle electronics and sounds a warning when a preset speed is exceeded. A nice simple project for a PIC perhaps. OK this could be done via a GPS unit but keep it simple I say ?
The snag is where do you find this 'speed' signal ? There was mention of such magic signal in the 'Tiptronic-style Gear Indicator' article in EPE Jan 2006 but the article suggested (alternatively) creating your own signal with pickups and magnets on drive shafts etc. The Speedguard site reveals all but only after you have bought a unit (fair enough !). It has been suggested (by internet research) that car radios utilise this signal to adjust the volume. I assume that is a digital pulse but some writer seemd to think it was an analogue control voltage ? (I think not ?)
Next thought is about the user interface and function - the Speedguard unit has only a single preset warning (I think) but I would prefer warnings at 30, 40, 50 mph for example. Any ideas anyone ? Head-up LED displays? Audio tones ?
Just an idea here as a new member - what about a collective project that could then be published in the magazine ? OK so no financial reward for the contributors but might keep the magazine supplied with some UK articles ? |
Mikehibbett
Frequent Contributor
Username: Mikehibbett
Post Number: 396
Registered: 04-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, 18 April, 2006 - 10:58 pm: |
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well, I'm a bit biased, but you could look at the website in my sig.
That uses a GPS receiver to determine the road speed.
Chances are your weblinked unit gets its data from the car's diagnostics port, which is present on the console on most modern cars. ODB-2 connector I think.
The speed limit indicator is a real eye-opener. Mine is always going off :o)
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www.drivesentinel.co.uk - Home build GPS Speed Camera Detectors
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Istedman
Frequent Contributor
Username: Istedman
Post Number: 54
Registered: 05-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, 18 April, 2006 - 11:17 pm: |
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Hi,
The speed signals present on most modern (post 2001) cars uses the CAN bus interface. If an appropriate radio is fitted, it detects the increased speed and increases the radio volume.
On a standard ISO connector, the speed signal is on the part that has the power connections, I can not recall the pin number/wiring colour but I found it on a VW/Skoda forum.
A PIC can easily interface to a CAN bus, Microchip even make CAN bus chips but I do not know what message you need to look for.
Sorry I could not help more, I hope I have given you some ideas though.
Ian |
Riki
Frequent Contributor
Username: Riki
Post Number: 57
Registered: 10-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, 19 April, 2006 - 12:28 am: |
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Been there,done it.
Use Lassen/trimble 25 quid stamp GPS.Connects a PIC on RS232 output line 4800 and then interogate the data after VTP occurs in data stream to get speed.Connect simple switch on another PIC line and when pressed the realtime speed goes into memory.If speed is exceeded a beeper bleeps.So any speed can be set.
Thing is though I road tested my unit for two days and as far as I,m concerned it constitutes a safety hazard.And have you tried driving in a 30 mph zone for any length of time and never never exceeding that speed ?Pain in the butt to put it mildly.
Still with a RS232/USB interface and a small laptop U have very cheep GPS and can also listen to yer MP3's @ same time.The GPS unit powered via the 5 volt USB line.+3.3 voltage regulator.
I was always under the impresssion that GPS was highly complex and it is very complex signals eminating from the 24 satellites but the o/p is NMEA protocol RS232.Simple. |
Petelobus
Frequent Contributor
Username: Petelobus
Post Number: 111
Registered: 06-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, 19 April, 2006 - 08:20 am: |
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I don't think that, even on post 2001 cars, the speed signal is in a standard format, or even necessarily available from the diagnostic (OBD) socket. All the manufacturers are required to provide on this socket are diagnostics for the engine/emissions equipment, and even this can, I think, be in one of three formats. Some car radios do use a speed signal to adjust the volume, but again, this is not standardized. Finding info on this sort of stuff is almost impossible! Some of the manufacturer specific websites can (occasionally) be of assistance, also if you can ask your local garage nicely, they may let you look at the AutoData, or similar listing for your car, which may show which pin (if any) on the engine ECU receives a speed signal, and also the loction of said ECU. Maybe the GPS is the easiest route!
Ian |
Grab
Frequent Contributor
Username: Grab
Post Number: 164
Registered: 05-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, 19 April, 2006 - 11:34 am: |
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I've only worked on Ford, Fiat and PSA so far, so I don't know about GM or other places. But vehicle speed is a standard feature on OBD for all those, and I suspect it would be on others too, althought I can't remember if it's a legislative requirement. It's a standard item in OBD service $01 though, and you don't need any special security to get to it (beyond knowing the OBD protocol).
Speed usually comes over CAN from the ABS these days, usually reported as four separate wheelspeeds. You can try and sniff these from the CAN directly, but it'll be a pretty tough job. Getting the info from the OBD diagnostics interface will be much easier.
Graham. |
Mikehibbett
Frequent Contributor
Username: Mikehibbett
Post Number: 397
Registered: 04-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, 19 April, 2006 - 01:43 pm: |
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Graham, you obviously know something about the subject, are you able to answer this question that I've been thinking about:
Is it 'safe' to be constantly accessing the diagnostics interface while the vehicle is in use?
I'm just a little worried that my polling of useful parameters, such as coolant temperature, speed, RPM etc might interfere with the normal operation of the ECU. I'd rather not crash the thing while doing 70 on a motorway!
Mike.
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www.drivesentinel.co.uk - Home build GPS Speed Camera Detectors
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Grab
Frequent Contributor
Username: Grab
Post Number: 166
Registered: 05-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, 19 April, 2006 - 06:08 pm: |
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It's perfectly safe to use the diagnostics interface any time. I should hope it is anyway, since I've been doing that for over a year on the new Ford Transit and Fiat Ducato. ;-)
Seriously, diagnostics has loads of checks to make sure that you can't do anything silly like ask for reflashing while you're doing 70 down the motorway. If you ask for something that's unsafe, it'll just say no (or *should* anyway, assuming the engineers had half a clue when they designed it). Reading speeds and temperatures is fine - as far as that goes, the only way it could interfere with normal running would be to take too much processing time, and that should have been tested before the software was ever released. Realistically, reporting this kind of stuff takes very little load on most processors - it's just reading the value of an existing variable, possibly with some extra scaling applied, and bunging it out on the CAN interface.
Sniffing data off the ABS CAN bus is a lot more dodgy. So long as it just reads and doesn't write (and it's correctly terminated), then anything else on the CAN bus (like a PIC or whatever) shouldn't interfere with it. But I'm not sure I'd want to risk it, since most systems now send stuff between the modules over CAN instead of each module having its own sensors. A knackered CAN bus usually results in the vehicle stopping and refusing to start, or if you're lucky then it'll go to limp-home mode and you can just about get back home with limited RPM and power.
Graham.
PS. I've moved off the vans now. Bit of a change of tack - the current project is for Aston Martin, working on the software for the DB9 and V12 Vanquish. :-) The word is that we might just be forced to do some testing on the Vanquish at our place next week, which means someone is just going to have to drive it around a bit, possibly including 2.5-hour runs each way between Gaydon to Cambridge to get it here and back. And we're not going to fight over who gets to do the driving, not much, honest... ;-)
(Message edited by grab on 19 April, 2006) |
Mikehibbett
Frequent Contributor
Username: Mikehibbett
Post Number: 399
Registered: 04-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, 19 April, 2006 - 06:56 pm: |
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Thanks, very interesting!
Mike.
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www.drivesentinel.co.uk - Home build GPS Speed Camera Detectors
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Mikemeakin
Just joined
Username: Mikemeakin
Post Number: 2
Registered: 04-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, 19 April, 2006 - 07:09 pm: |
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Gentlemen,
Thanks for your very helpful and constructive replies and comments. It seems that the OBD connector or the radio connector is the place to 'poke around' but am wondering whether this is actually a 'useful' device to make as a number of posters say that it gets very annoying to be constantly reminded of your speed ! The trouble is with all the 30,40,50 MPH zones it is SO easy to 'forget' and find yourself well over the limit !! I've read where they are 'doing' drivers for a mere 3MPH over the 30 limit and I don't want to be one of them.
Hence the questions on 'User Interface' - I thought of continuous warning tones at the various speeds but not so sure about this now? Another idea was some sort of head-up LED display on the windscreen as it is very difficult to concentrate on the speedo reading and drive the car as well ! Any other thoughts from anyone ?
The actual electronics is fairly easy (I imagine) an 8 pin PIC and we have it.
P.S Am I correct in thinking that some GPS systems utilise the vehicle 'speed' signal to correct for loss of signal ? How do THEY get their signal I wonder ?
www.nikamelectronics.co.uk
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Externet
Regular Contributor
Username: Externet
Post Number: 49
Registered: 05-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, 20 April, 2006 - 01:31 am: |
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Hello !
..."but keep it simple I say ? "...
Get a speedometer with alarm from a bicycle store and affix it to the driveshaft.
Miguel  |
Petelobus
Frequent Contributor
Username: Petelobus
Post Number: 112
Registered: 06-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, 20 April, 2006 - 09:43 am: |
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I've thought a bit about the interface (it always the hardest part in these jobs), and wondered if a slowly increasing audible signal would be appropriate (i.e. just sounding at 1mph over, getting to annoying at 5mph over). Some sort of steering column mounted stalk to set the target speed? I think that you'd need to tell the unit what the speed limit was when you entred the zone, as any 'always on' signal would either be really annoying, or terribly easy to ignore. Otherwise, how about 3 LEDs projected onto the screen (one for 30, one for 40 and one for 50 say) off when the speed is below the set point, and either changing colour, or increasing intensity as the speed exceeded the set point?
Just a few first thoughts.
Ian |
Mikemeakin
Just joined
Username: Mikemeakin
Post Number: 3
Registered: 04-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, 20 April, 2006 - 11:20 am: |
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Really like the idea of the bike speedo but still need a 'speed' signal.- usually a magnet on wheel and reed switch or hall-effect sensor on the frame ?
Also like the three projected LEDs on windscreen as user interface - I had something like this in mind.
www.nikamelectronics.co.uk
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Externet
Regular Contributor
Username: Externet
Post Number: 50
Registered: 05-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, 20 April, 2006 - 04:53 pm: |
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Hi.
? I do not understand the part ..." I need the signal"...
A bicycle speedometer -digital display- not a mechanical one. Has the "signal"
Has the LCD readout, installs with a magnet on any spinning shaft, inexpensive, compact. Go to a store and take a look. Perhaps you can choose on the net.
What I do not know which model would have more than one speed alarm. Get two and set different limits?
Miguel |
Mikemeakin
Just joined
Username: Mikemeakin
Post Number: 4
Registered: 04-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, 20 April, 2006 - 06:59 pm: |
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OK, sorry was not thinking clearly here ! Of course the bike speedo is a complete 'system' with sensor and read out. As you correctly point out all I need is a rotating component (wheel, drive shaft ?) to which I attach a magnet. I actually have a 'wireless' one somewhere in my workshop but range from sensor to readout is only a foot or so and uses 'magnetic' communications. Don't think this will work very well in car so may have a browse for a standard version.
Thanks
www.nikamelectronics.co.uk
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Dave_g
Frequent Contributor
Username: Dave_g
Post Number: 110
Registered: 05-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, 23 April, 2006 - 12:23 pm: |
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Sorry to have to take it back to "blokes things", but if Graham needs a hand with that Vanquish, he only has to ask. After all, he's a young man in that thumbnail, perhaps a more experienced (older) driver would be a better test of his software. Honest.
Now that's a job I could be envious of..... |
Grab
Frequent Contributor
Username: Grab
Post Number: 174
Registered: 05-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, 24 April, 2006 - 12:45 pm: |
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Believe me, you don't want to get too envious, Dave - not after 18 months spent designing diagnostics for Transit vans. I must have done something *very* bad in a past life... |
Dave_g
Frequent Contributor
Username: Dave_g
Post Number: 111
Registered: 05-2005
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, 24 April, 2006 - 10:20 pm: |
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Graham - perhaps thats why white vans go so fast - you're reusing that same software!!! |
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