The law here in New Jersey requires a road vehicle's headlights to be on whenever its windshield wipers are on. An EE forgot and was ticketed. Resolving that he would never repeat the infraction, he wired the wiper motor through a diode to the headlight relay, so that the lights came on whenever the motor was running. A few weeks later, he was driving down the interstate in a light rain and noticed a police car keeping a steady distance behind him. A few miles down the road, there were flashing lights and lanes blocked. He slowed down, then found his car hemmed in by police cars. A PA horn blared for him to keep his hands in sight on the wheel; policemen aimed guns at him from both sides of the car, and the PA demanded that he unlock the doors. His shouts that he couldn't do that with his hands on the wheel went unheard through the closed windows, but one policeman noticed him trying to shout and with the PA silenced, finally heard what he was saying. With guns pointed at him from both sides, he was ordered to unlock the door, but move slowly. As soon as it unlocked, a policeman tried to pull him out without success. Seat belt. Finally, they ordered him out of the car on his own power -- slowly, of course, and patted him down. The name on his photo drivers license matched the registration in the glove compartment, and they concluded that his silent theft alarm must have malfunctioned. He and they were puzzled: his car wasn't equipped with an alarm of any kind. Finally, a sergeant who had until then been sitting out of the rain in one of the patrol cars noticed that his headlights blinked in time with his intermittent wipers. Mystery solved! Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
An unfortunate design bug
Started by ●June 1, 2004
Reply by ●June 1, 20042004-06-01
> The law here in New Jersey requires a road vehicle's headlights to be on > whenever its windshield wipers are on.Do they have to be on when you press the windshield wash button and wipe the spray off? Sounds a little extreme. "Jerry Avins" <jya@ieee.org> wrote in message news:40bbf8ca$0$3137$61fed72c@news.rcn.com...> The law here in New Jersey requires a road vehicle's headlights to be on > whenever its windshield wipers are on. An EE forgot and was ticketed. > Resolving that he would never repeat the infraction, he wired the wiper > motor through a diode to the headlight relay, so that the lights came on > whenever the motor was running. > > A few weeks later, he was driving down the interstate in a light rain > and noticed a police car keeping a steady distance behind him. A few > miles down the road, there were flashing lights and lanes blocked. He > slowed down, then found his car hemmed in by police cars. > > A PA horn blared for him to keep his hands in sight on the wheel; > policemen aimed guns at him from both sides of the car, and the PA > demanded that he unlock the doors. His shouts that he couldn't do that > with his hands on the wheel went unheard through the closed windows, but > one policeman noticed him trying to shout and with the PA silenced, > finally heard what he was saying. > > With guns pointed at him from both sides, he was ordered to unlock the > door, but move slowly. As soon as it unlocked, a policeman tried to pull > him out without success. Seat belt. Finally, they ordered him out of the > car on his own power -- slowly, of course, and patted him down. > > The name on his photo drivers license matched the registration in the > glove compartment, and they concluded that his silent theft alarm must > have malfunctioned. He and they were puzzled: his car wasn't equipped > with an alarm of any kind. Finally, a sergeant who had until then been > sitting out of the rain in one of the patrol cars noticed that his > headlights blinked in time with his intermittent wipers. Mystery solved! > > Jerry > -- > Engineering is the art of making what you want from things you can get. > ����������������������������������������������������������������������� >
Reply by ●June 1, 20042004-06-01
On Mon, 31 May 2004 23:32:25 -0400, Jerry Avins <jya@ieee.org> wrote:>The law here in New Jersey requires a road vehicle's headlights to be on >whenever its windshield wipers are on. An EE forgot and was ticketed. >Resolving that he would never repeat the infraction, he wired the wiper >motor through a diode to the headlight relay, so that the lights came on >whenever the motor was running. > >A few weeks later, he was driving down the interstate in a light rain >and noticed a police car keeping a steady distance behind him. A few >miles down the road, there were flashing lights and lanes blocked. He >slowed down, then found his car hemmed in by police cars. > >A PA horn blared for him to keep his hands in sight on the wheel; >policemen aimed guns at him from both sides of the car, and the PA >demanded that he unlock the doors. His shouts that he couldn't do that >with his hands on the wheel went unheard through the closed windows, but >one policeman noticed him trying to shout and with the PA silenced, >finally heard what he was saying. > >With guns pointed at him from both sides, he was ordered to unlock the >door, but move slowly. As soon as it unlocked, a policeman tried to pull >him out without success. Seat belt. Finally, they ordered him out of the >car on his own power -- slowly, of course, and patted him down. > >The name on his photo drivers license matched the registration in the >glove compartment, and they concluded that his silent theft alarm must >have malfunctioned. He and they were puzzled: his car wasn't equipped >with an alarm of any kind. Finally, a sergeant who had until then been >sitting out of the rain in one of the patrol cars noticed that his >headlights blinked in time with his intermittent wipers. Mystery solved! > >JerryHey Jerry, that's a pretty cute (and scary) story. My first reaction, as an engineer, was: Test your design, very thoroughly, before deploying your system "in the field". [-Rick-]
Reply by ●June 1, 20042004-06-01
KG7HF wrote:>>The law here in New Jersey requires a road vehicle's headlights to be on >>whenever its windshield wipers are on. > > Do they have to be on when you press the windshield wash button and wipe the > spray off? Sounds a little extreme.I don't believe the law actually addresses that, but in practice, no. There's an unconfirmed story of someone driving home in heavy rain without wipers because the headlights wouldn't go on. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●June 2, 20042004-06-02
Jerry Avins <jya@ieee.org> wrote in message news:<40bd2c88$0$2968$61fed72c@news.rcn.com>...> KG7HF wrote: > > >>The law here in New Jersey requires a road vehicle's headlights to be on > >>whenever its windshield wipers are on. > > > > Do they have to be on when you press the windshield wash button and wipe the > > spray off? Sounds a little extreme. > > I don't believe the law actually addresses that, but in practice, no. > There's an unconfirmed story of someone driving home in heavy rain > without wipers because the headlights wouldn't go on. > > JerryI had an experience like that just last week, when returning to work after a week off. I was supposed to drive some 700 km that day, and about half way I passed through a small town, roundabouts and all. When I checked my speed against the speed limits when entering the town, the speedometer worked. When I checked the speed limits after having driven straight throuh the town, nothing worked. Speedometer flat. Temperature ice cold. No revs showing on the counter. No direction indicators. In short, the whole instrument panel was dead. Of course, I immediately pulled over and made the quick checks in the engine compartment to see that nothing burned. After some time I found a fuse that was popped. I changed it and the thing popped again after 3 seconds. OK, this was last sunday and I was 400 km from home, so there was nothing to do but find a lodging and stay in town until monday and have some professional look at it. The problem turned out to be the cable to the trailer hook. It had come loose under the bumper, and had hung against the hot exhaust pipe, burning the insulation and eventually short-cirquited the direction indicator wire to the exhaust pipe. This course(?) supplied power to both the direction indicator lights all around the car and the instrument panel. The fuse had blown when I used the direction indicator in a roundabout. The repairs were easy, just some tape for insulation and a strip to fix the cable in place. But man, did I curse whoever designed the system so that a simple short cirquit at the trailer cable would kill the instrument panel. Almost as much as I cursed myself for not having fixed that cable, that I knew was loose, before. Rune
Reply by ●June 2, 20042004-06-02
"Rune Allnor" <allnor@tele.ntnu.no> wrote in message news:f56893ae.0406012347.11c9c1ff@posting.google.com...> But man, did I curse whoever designed the system so that a simple > short cirquit at the trailer cable would kill the instrument panel. > Almost as much as I cursed myself for not having fixed that cable, > that I knew was loose, before. > > RuneHello Rune, The linkage between the tail lights and the instrument panel lights was an old design criterion so that the driver could tell when his tail lights were off (due to lack of power because the panel would also be dark). So I see the whole panel dying from this as being a consequence of this legacy design. Nowadays, with auto electrical systems having more than a couple of fuses, a smarter approach can be had. When I added a trailer hitch to my car (a 2001 model), the wiring harness actually connects to the power harness with its own fuse and uses circuitry to monitor the tail/turn/brake lights. The design allows for any combination of short circuits in a trailer without stopping the operation of the car's lights. Of course the fuse that supplies the trailer's power will fail - but it is supposed to. -- Clay S. Turner, V.P. Wireless Systems Engineering, Inc. Satellite Beach, Florida 32937 (321) 777-7889 www.wse.biz csturner@wse.biz
Reply by ●June 2, 20042004-06-02
"Clay S. Turner" <CSTurner@WSE.Biz> wrote in message news:<55lvc.4889$2M1.924@bignews3.bellsouth.net>...> "Rune Allnor" <allnor@tele.ntnu.no> wrote in message > news:f56893ae.0406012347.11c9c1ff@posting.google.com... > > But man, did I curse whoever designed the system so that a simple > > short cirquit at the trailer cable would kill the instrument panel. > > Almost as much as I cursed myself for not having fixed that cable, > > that I knew was loose, before. > > > > Rune > > > Hello Rune, > > The linkage between the tail lights and the instrument panel lights was an > old design criterion so that the driver could tell when his tail lights were > off (due to lack of power because the panel would also be dark). So I see > the whole panel dying from this as being a consequence of this legacy > design.Interesting. I didn't know that. Perhaps this thing is mentioned in the instruction book. I never read it. Still, I think it's a pretty drastic way of warning...> Nowadays, with auto electrical systems having more than a couple of > fuses, a smarter approach can be had. When I added a trailer hitch to my car > (a 2001 model), the wiring harness actually connects to the power harness > with its own fuse and uses circuitry to monitor the tail/turn/brake lights. > The design allows for any combination of short circuits in a trailer without > stopping the operation of the car's lights. Of course the fuse that supplies > the trailer's power will fail - but it is supposed to.Perhaps I'm too much of an engineer... this is how I expected things to be. Well, one learns something new every day. Rune
Reply by ●June 2, 20042004-06-02
Another thing, possibly in the same vein, is that on my car when one turn signal bulb is out, the whole turn signal flashes considerably faster than normal. I've always assumed this was to warn the driver about something they might otherwise not notice for months. I'm sure nowadays it would be easy to design it so that the flashing rate was independent of how many bulbs were connected, but that seems like a nice warning system, and much less "destructive" than having your whole instrument panel go out. "Rune Allnor" <allnor@tele.ntnu.no> wrote in message news:f56893ae.0406021035.41d2d2ee@posting.google.com...> "Clay S. Turner" <CSTurner@WSE.Biz> wrote in messagenews:<55lvc.4889$2M1.924@bignews3.bellsouth.net>...> > "Rune Allnor" <allnor@tele.ntnu.no> wrote in message > > news:f56893ae.0406012347.11c9c1ff@posting.google.com... > > > But man, did I curse whoever designed the system so that a simple > > > short cirquit at the trailer cable would kill the instrument panel. > > > Almost as much as I cursed myself for not having fixed that cable, > > > that I knew was loose, before. > > > > > > Rune > > > > > > Hello Rune, > > > > The linkage between the tail lights and the instrument panel lights was an > > old design criterion so that the driver could tell when his tail lights were > > off (due to lack of power because the panel would also be dark). So I see > > the whole panel dying from this as being a consequence of this legacy > > design. > > Interesting. I didn't know that. Perhaps this thing is mentioned in the > instruction book. I never read it. Still, I think it's a pretty drastic > way of warning...
Reply by ●June 2, 20042004-06-02
Jon Harris wrote:> Another thing, possibly in the same vein, is that on my car when one turn signal > bulb is out, the whole turn signal flashes considerably faster than normal. > I've always assumed this was to warn the driver about something they might > otherwise not notice for months. I'm sure nowadays it would be easy to design > it so that the flashing rate was independent of how many bulbs were connected, > but that seems like a nice warning system, and much less "destructive" than > having your whole instrument panel go out.I don't know if that was originally intentional, but it's been that way at least 40 years and its usefulness is evident. A bothersome side effect is that the timing becomes barely with the additional load of trailer lights. special "heavy duty" flashers whose timing is independent of load are available as replacements for that use. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●June 2, 20042004-06-02
Jerry Avins wrote:> Jon Harris wrote: > >> Another thing, possibly in the same vein, is that on my car when one >> turn signal >> bulb is out, the whole turn signal flashes considerably faster than >> normal. >> I've always assumed this was to warn the driver about something they >> might >> otherwise not notice for months. I'm sure nowadays it would be easy >> to design >> it so that the flashing rate was independent of how many bulbs were >> connected, >> but that seems like a nice warning system, and much less "destructive" >> than >> having your whole instrument panel go out. > > > I don't know if that was originally intentional, but it's been that way > at least 40 years and its usefulness is evident. A bothersome side > effect is that the timing becomes barely with the additional load of^ tolerable> trailer lights. special "heavy duty" flashers whose timing is > independent of load are available as replacements for that use. > > Jerry-- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
