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diy rpm activated switch.

Old 01-10-2004, 03:33 PM
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Default diy rpm activated switch.

I was reading in the january issue of honda tuning about a guy that made is own switch using a 30 amp relay. I thought about it and it could possibly be done by using resistors to prevent the relay from closing until a certain rpm (the tach signal would have resistors between it and the relay). Has anybody tried this or does anyone have any ideas or input? What happened to shortyz list of resitors compared to the rpm the correspond to on the autometer shift light?

I'll try this and let you all know how it turns out. testing will be done by the end of february because I'm lazy like that.
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Old 01-10-2004, 06:22 PM
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Default Re:diy rpm activated switch.

Kyle thats a good question. I'd be interested in knwing how to build an rpm switch myself for a future swap.
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Old 01-10-2004, 09:39 PM
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Default Re:diy rpm activated switch.

I just asked this same q in another post, but somewhat on topic, do you know what kind of signal the tach gets? I wanted to make a gauge, but someone told me it gets voltage pluses, whatever that means whereas I assumed it gets a steady signal that rises with rpm. If it gets a different sort of signal (sounds almost like a/c but all in the positive I got no idea what voltage pluses are) seems like it would be hard to implement this.
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Old 01-10-2004, 10:19 PM
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Default Re:diy rpm activated switch.

OKay, I'll try ot make it short and simple. RPM = Revolution Per Minute, which refers to the number of times the crankshaft turns in one minute. RPM signals are normally taken from the ignition circuit that controls the ignition coil. The ignition coil fires every time the ignitor tells it to. This on/off/on/off firing of the coil produces a spark for each time the coil is switched off (I can explain further on the "off" if you like, but you'll need to understand what "magnetic lines of flux" are all about). A fixed number of sparks are created for each revolution of the crank. As RPM increases this on/off/on thing happens quicker and quicker, because the coil is still must generate the same number of sparks per revolution, even if the revolutions are getting quicker due to rising RPM. When you tap into the coil control signal, you see the on/off/on/off cycle as 12V/0V/12V/0V. This actually occurs so quickly, that you cannot see it with a voltmeter, it takes a scope. Each 12V portion is called a positive pulse. The Tachometer, reads the number of pulses per minute, and converts this to an RPM value.

Whew!

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Old 01-11-2004, 04:22 PM
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Default Re:diy rpm activated switch.

well, i'm no EE, but a 2907 freq>voltage converter and an lm311 comparator should do what you want it to. a 339 quad comparator could be used if you wanted to activate more than 1 thing..

here's a schematic i drawed up..


if you want a full sized pic, PM me and i'll email it to you.. imagestation seems to like shrinking my ---- lately..

this is for a positive response circuit, meaning it turns on when at and above a certain rpm level. if you want a negative response circuit, meaning if you want the switch to be on below a certain rpm level and turn off when you reach a set rpm, all you have to do is switch pins 2 and 3 on the 311 comparator.

hope this helps.. EE's, if i missed something, please correct it.
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Old 01-12-2004, 06:12 PM
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Default Re:diy rpm activated switch.

scarecrowx is a pimp. e-mail me the bigger picture please, I like going into radioshack and telling them they can't help me. [email protected]
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Old 01-14-2004, 03:51 PM
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Default Re:diy rpm activated switch.

I got the schematic, I just need to build this now, once it's done I'll borrow a camera since I can't find mine and put some picts up.
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Old 01-21-2004, 02:00 PM
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Default Re:diy rpm activated switch.

IF you can set it to turn on and off at certain RPM... you could use it to controll your nitrous to spool up your TURbo's JUst put it in a fancy little box.... maybe a LED to let you know its activated.. and your good to go
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Old 01-21-2004, 06:03 PM
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Default Re:diy rpm activated switch.

pm me vigorhn
thanks
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Old 01-22-2004, 01:27 AM
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Default Re:diy rpm activated switch.

Originally Posted by dastinker8
IF you can set it to turn on and off at certain RPM... you could use it to controll your nitrous to spool up your TURbo's JUst put it in a fancy little box.... maybe a LED to let you know its activated.. and your good to go
good call on the LED.

it could also control ITB and VTEC (honda) or TVIS (toyota).

if anyone's wondering, ITB and TVIS are variable intake runner systems by each of those manufacturers. at least on the toyota, people saw about 10 ft-lb gains in low to mid range by holding the valves closed longer than stock.

for the ITB and TVIS controls though, they would have to be negative response circuits. the ECU opens the shorter/bigger runners by ungrounding the actuator solenoid.
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