"Jerry Avins" <jya@ieee.org> wrote in message news:40be6f5e$0$2965$61fed72c@news.rcn.com...> 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.Anyone know how that circuit works that changes the timing when one light blows?
An unfortunate design bug
Started by ●June 1, 2004
Reply by ●June 2, 20042004-06-02
Reply by ●June 2, 20042004-06-02
"Jon Harris" <goldentully@hotmail.com> wrote in message news:2i7b95Fjugh9U1@uni-berlin.de...> "Jerry Avins" <jya@ieee.org> wrote in message > news:40be6f5e$0$2965$61fed72c@news.rcn.com... > > 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 thatway> > > 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. > > Anyone know how that circuit works that changes the timing when one lightblows?> >Hello Jon, The turn signal circuits use bimetalic switches that open when they heat up from the pass through current. When a bulb burns out, the switch heats up less (opens less) and the cycle between heating and cooling is less, hence a higher flash frequency. Not fancy - but it is cheap and amazingly reliable. -- 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
Jon Harris wrote:> "Jerry Avins" <jya@ieee.org> wrote in message > news:40be6f5e$0$2965$61fed72c@news.rcn.com... > >>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. > > > Anyone know how that circuit works that changes the timing when one light blows?The ur-flasher is thermal. Current to the lamps passes through a coil around a bimetal strip which curls when hot, breaking the circuit. Contact is re-established when the strip cools. A normal load results in approximately a 50% duty cycle. A burned-out bulb causes a long on time and a shortened off time, while connecting a trailer causes the lights to be on in brief blinks. Nowadays, it's probably simulated by the dashboard computer. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●June 3, 20042004-06-03
. 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, this seems too simple because no one asked this question, but I cannot understand why the blinking of headlights was taken as a possible theft? Could you please explain a bit more. Regards, Ishtiaq.
Reply by ●June 3, 20042004-06-03
On Thu, 3 Jun 2004 13:59:22 +0900, "I. R. Khan" <ir_khan@hotmail.com> wrote:> >. 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, this seems too simple because no one asked this question, but I >cannot understand why the blinking of headlights was taken as a possible >theft? Could you please explain a bit more.Many third-party (third-rate?) alarms for cars in the USA, when alarming, flash the headlights (as well as sounding the horn or a siren which others would presume this driver disconnected).>Regards, >Ishtiaq.----- http://mindspring.com/~benbradley
Reply by ●June 3, 20042004-06-03
I. R. Khan wrote:> . 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, this seems too simple because no one asked this question, but I > cannot understand why the blinking of headlights was taken as a possible > theft? Could you please explain a bit more. > > Regards, > Ishtiaq.There is apparently a theft alarm on the market that causes the headlights to blink without providing any indication inside the car if the engine is not started with a specific device. This alerts police to a stolen car even when the driver doesn't behave suspiciously. I was once stopped by a State Trooper who brusquely ordered me out of my car. When we were safely away from my passenger (a hitch hiker) he asked in a friendly tone if I needed help. I had inadvertently left my hazard flashers on after I picked the fellow up, and the trooper thought it might be a call for help. I thanked him; it's comforting to be looked after. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●June 3, 20042004-06-03
"Clay S. Turner" <CSTurner@WSE.Biz> wrote in message news:AJuvc.6753$Ua7.4533@bignews2.bellsouth.net...> > "Jon Harris" <goldentully@hotmail.com> wrote in message > news:2i7b95Fjugh9U1@uni-berlin.de... > > > > > > > Jon Harris wrote: > > > > Anyone know how that circuit works that changes the timing when one light > blows? > > Hello Jon, > > The turn signal circuits use bimetalic switches that open when they heat up > from the pass through current. When a bulb burns out, the switch heats up > less (opens less) and the cycle between heating and cooling is less, hence a > higher flash frequency. Not fancy - but it is cheap and amazingly reliable.Neat! I could have written some mean DSP code to do that, but I figured there must a simpler way. :-)
Reply by ●June 3, 20042004-06-03
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.My Dad tells a story about something he did to one of his friends once. It involved using a safety pin to connect the wire that feeds the brake lights to the wire that feeds the horn. ;-) -- Jim Thomas Principal Applications Engineer Bittware, Inc jthomas@bittware.com http://www.bittware.com (703) 779-7770 There's a fine line between clever and stupid
Reply by ●June 7, 20042004-06-07
Clay S. Turner wrote:> The turn signal circuits use bimetalic switches that open when they heat up > from the pass through current. When a bulb burns out, the switch heats up > less (opens less) and the cycle between heating and cooling is less, hence a > higher flash frequency. Not fancy - but it is cheap and amazingly reliable.I thought most now used semiconductor based flash controllers. The bimetal strip devices were too failure prone. For safety reasons, the new ones still sense the current and indicate bulb failure in some way. The old ones would usually not flash at all, and one would manually flash them with the turn signal switch. -- glen
