rpm signal from cigarette lighter? - Miata Turbo Forum -Boost cars, acquire cats.

Welcome to Miataturbo.net   Members

Insert BS here A place to discuss anything you want

LinkBack Thread Tools Search this Thread
Old 06-27-2009, 04:17 PM   #1
I'm Miserable!
Thread Starter
iTrader: (16)
Join Date: Dec 2008
Location: where most people are Utarded
Posts: 1,323
Total Cats: 0
Default rpm signal from cigarette lighter?

I saw this SHIFT LAMP CONTROL UNIT BLACK W/RED LED HYUNDAI SCION:eBay Motors (item 120429796394 end time Jul-03-09 12:46:19 PDT) and wonder exactly how it works?
zoomin is offline   Reply With Quote
Old 06-27-2009, 04:41 PM   #2
Junior Member
iTrader: (3)
Join Date: Mar 2008
Location: Dallas, Carrollton, Tx
Posts: 181
Total Cats: 6

Looks like a knock off of the Pivot shift light. I had the Pivot version on my old integra, it worked pretty well. The only time it didn't work was when the alternator started to fail.
Fidgitk is offline   Reply With Quote
Old 06-27-2009, 05:05 PM   #3
Boost Pope
iTrader: (8)
Joe Perez's Avatar
Join Date: Sep 2005
Location: Chicago
Posts: 24,430
Total Cats: 1,528

Originally Posted by zoomin View Post
wonder exactly how it works?
Not very well.

Seriously, though. It senses the electrical noise produced by the alternator. Since the alternator generates AC internally and then rectifies it to DC through a simple diode stack, the current waveform coming out of it has a fair bit of ripple. If viewed on an oscilloscope, you'd see that it's not a nice, smooth 14 volts, but rather that it has a high-frequency noise component that varies in frequency as to the speed at which the alternator is turning.

By sensing this ripple, you can derive an imprecise approximation of engine RPM. There is no absolute relationship of the noise frequency to engine RPM, as it varies with the pulley ratio, which is why the device is adjusted by a couple of analog potentiometers rather than something scaled in exact RPM. If methodically adjusted, it will probably be accurate to +/- a couple hundred RPM.
Joe Perez is online now   Reply With Quote
Old 06-27-2009, 06:02 PM   #4
Senior Member
iTrader: (2)
SamS's Avatar
Join Date: Jun 2006
Location: Wisconsin
Posts: 1,230
Total Cats: 3

The g-tech pro uses that method for rpm signal, it's got several different pickup modes built in so you can pick the one that is most accurate for your car. It's within about 100 rpm of my tachometer.
SamS is offline   Reply With Quote
Old 06-28-2009, 11:06 AM   #5
Elite Member
iTrader: (1)
Join Date: Jun 2005
Location: Charleston, SC
Posts: 2,976
Total Cats: 14

I built a "dyno" out of a voice recorder (and some software), cig plug, and old timing light. So, Yes, you can get RPM from it...
rmcelwee is offline   Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
My solution for Oiltemp and Oilpressure input into Megasuirt (MS3) Zaphod MEGAsquirt 41 01-24-2016 12:25 PM
CAS weirdness Asx MEGAsquirt 5 12-15-2015 11:14 AM
Low oil pressure after 1.8 swap and new turbo setup JesseTheNoob DIY Turbo Discussion 15 09-30-2015 02:44 PM
Are my coils failing? viriiguy General Miata Chat 5 09-28-2015 07:39 PM
ms2e No Rpm Signal Dobzeh ECUs and Tuning 5 09-17-2015 02:56 PM

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 03:53 PM.