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Mysticle31
Apprentece
USA
13 Posts |
 Posted - Nov 03 2007 : 1:40:08 PM
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Hello again,
Thanks for your advice on my last project.
I got to wondering a couple things.
Is there a simple device or circuit that can monitor engine RPMs for a "one touch" start? So I press the start button, the engine cranks, and then when the RPMs jump the starter will disengage.
I know many remote start systems employ this kind of feature. I don't want a remote start system, but I do want to experiment with one touch start. Any ideas?
Also,
Is there such a thing as a relay with an infinite timer? Standard relays only click on with current across the coil, timed relays only operate for a short period of time. I want a relay that will click closed the NO pin and stay closed until something else happens without needing to have a coil powered. Anything? |
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YUSHA
Apprentece
11 Posts |
Posted - Nov 28 2007 : 6:24:50 PM
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Hi,there used to be time delay relays that had a worked with a vaccum device build it which after relay was engaged would then slowly release points after a preset time by letting air escape from air chamber.They were not really that big and needed no more power to change back to normally open.
yusha |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Nov 29 2007 : 09:11:54 AM
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quote:
Originally posted by Mysticle31
Hello again,
Thanks for your advice on my last project.
I got to wondering a couple things.
Is there a simple device or circuit that can monitor engine RPMs for a "one touch" start? So I press the start button, the engine cranks, and then when the RPMs jump the starter will disengage.
I know many remote start systems employ this kind of feature. I don't want a remote start system, but I do want to experiment with one touch start. Any ideas?
Off the top of my head, a circuit to read the ignition pulses off of one of the coils (check out the Megasquirt website for that bit of the circuit) which will output a pulse train. Then a PLL circuit (or even a "missing pulse detector" made with a 555 timer) to provide a steady signal once the frequency of pulses is high enough to constitute a running engine. That disengages a relay and latches it open (to prevent accidental activation should the engine stall).
quote:
Is there such a thing as a relay with an infinite timer? Standard relays only click on with current across the coil, timed relays only operate for a short period of time. I want a relay that will click closed the NO pin and stay closed until something else happens without needing to have a coil powered. Anything?
I can't see how it's possible to keep the NO pin connected without powering the coil in some way. Other then a mechanical latching device that is disengaged with a solenoid. |
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pebe
Nobel Prize Winner
United Kingdom
1078 Posts |
Posted - Nov 29 2007 : 10:45:33 AM
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quote:
Originally posted by Mysticle31
.....Is there such a thing as a relay with an infinite timer? Standard relays only click on with current across the coil, timed relays only operate for a short period of time. I want a relay that will click closed the NO pin and stay closed until something else happens without needing to have a coil powered. Anything?
There is a two-coil latching relay that needs no power to keep closed. See:
http://en.wikipedia.org/wiki/Relay |
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binaryblade
Apprentice
Canada
136 Posts |
Posted - Dec 15 2007 : 5:39:16 PM
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| Most Car engines have a tachometer, even if there isn't on in the dash there is probably a line feeding the computer. pull out your manual , some are analog others are a pulse train, should be no problem to tap into that. |
Suddenly I realize that I, like most of humanity, only know enough to be dangerous. |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Dec 16 2007 : 10:25:58 AM
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quote:
Originally posted by binaryblade
Most Car engines have a tachometer, even if there isn't on in the dash there is probably a line feeding the computer. pull out your manual , some are analog others are a pulse train, should be no problem to tap into that.
That's sort of true, sort of not. Most fuel injected cars made from the early '80s to the early '90s still used a distributor (there are exceptions to this of course, mostly from the Japanese) but fed the ECU with a trigger signal. In that case there is almost certainly a separate tach wire that runs from the coil into the cabin. The '84-'85 RX-7 is a good example of this. Fuel injection, with an electronic distributor.
By the end of the early '90s, nearly every car had moved to a totally electronic ignition with exception of some of the backwards domestic manufacturers. These systems use a trigger wheel to determine engine position. It is either a single wheel system with a wheel on the crank having a specific tooth pattern (ie. 60-2, 36-1, etc.) or a dual wheel system with both a crank and cam wheel to give the ECU a "home" and "sync" signal. The ECU then decides when to fire a coil pack. There's about a 50/50 chance that there's a real tach signal inside the car, but you can still get one from the negative side of the coil if need be. Also there may be a diagnostic plug designed to have a tach connected. 2nd gen RX-7s started using this system in '86 with a CAS (crank angle sensor) in place of the distributor. There's still a tach wire into the cabin to provide a signal for other modules (some cars have power steering and cruise control).
Furthermore, starting around 2000 for imports and a bit later (as usual...) for domestic, most vehicles have moved to a coil on plug system with the coils connected to the ECUs data bus. The ECU gets engine position as mentioned above. Getting a tach signal here is very hard as you would need to modify the coil to gain access to it's negative connection. This can imbalance the system (the ECU is very sensitive) and cause codes. My Insight uses this system, though has a completely different trigger based on the phases of the traction motor. |
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imp.sport
New Member
1 Posts |
Posted - Apr 26 2008 : 10:31:52 AM
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I am sure I have a VW relay that latches from open to closed and remains that way without any further input.
Sorry to say I don't know what car it was off since it was given to me by a guy who was clearing out his garage. I asked him what it was off but he didn't know. "I just filled his pockets with them when walking around scrap yards in the 80s" was what I recall him saying.
Hope this helps |
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Jonathan
New Member
1 Posts |
Posted - May 08 2008 : 02:42:22 AM
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| Most new model now a days does not have tacho line in the system because of using some sensor to detect the engine speed, and most ignition coil are direct ignition system having IGT Ignition timing signal from ECM Engine Control Management. |
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Topic |
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A simple circuit/device to monitor RPMs for start.
