Steve
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Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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Considering making up this electric diagram
The 12v will be from the +ve on a car battery. Am I right in thinking this will work in place for the "regulator"
http://cgi.ebay.co.uk/7808-Voltage-Regulator-x-2-pieces-7808-/350358288101?cmd=ViewItem&pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item5192fb36e5
Apparently thats rated at 12v to 8v step regulation.
Also does the -ve mean the - from the battery? and 0 volts = ground?
[Edited on 16-06-2010 by Steve]
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Dom
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Registered: 13th Sep 03
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0v is ground, -ve looks like an input from the neg side of a HT lead  Going by the V Out (and the fact the LM2917 is frequency to voltage converter) im assuming this converts RPM to a voltage (0-8v, 0-8krpm).
But yes that reg should work - pin 1 to +12v, pin 2 to 0v ground, pin 3 is the output (+8v). I would heatsink the reg as well.
edit - found a related thread - http://forum.allaboutcircuits.com/showthread.php?t=30186&page=5 as well as the original page - http://www.niksula.hut.fi/~mdobruck/siililand/mini/diy/alien/tacho/tacho.html
[Edited on 16-06-2010 by Dom]
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Steve
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yeah the -ve is from negative ht, anyone any ideas where i could pick that signal up from?
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oceansoul
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Is that not -ve on the LT side?
I wouldnt want to be putting the Volts of the HT lead on the IC 
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Dom
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quote:
Originally posted by oceansoul
Is that not -ve on the LT side?
I wouldnt want to be putting the Volts of the HT lead on the IC
LT?
You have a point though, HT voltage won't do the IC any favours 
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Steve
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LT side?
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Steve
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apparently according to an electronics forum
"The -ve is from the 'low' end of the ignition coil. the one that goes from the contact breaker contacts."
someone explain that to me please
[Edited on 16-06-2010 by Steve]
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Dom
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Possibly the ground side from the contact breaker? Could always get a DVM on that side and see what the voltage is....
Although this seems like serious ballache to convert the RPM to a voltage, it would be easier to grab something like an Arduino development board and try and convert the 'pulse' (or something other output from the ECU perhaps) that goes to rev counter....
Edit - Actually it could be the line from the ignition coil to contact breaker as that *should* be 12v
[Edited on 17-06-2010 by Dom]
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oceansoul
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quote:
Originally posted by Dom
Edit - Actually it could be the line from the ignition coil to contact breaker as that *should* be 12v
[Edited on 17-06-2010 by Dom]
This i belive. But that circuit looks as if its for an old fashioned car with a dizzy and points and coil n all that. A modern engine should give an RPM signal from either the coil pack, or the ECU.
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Steve
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theres 3 wires i believe going into my coilpack would it be one of them
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ed
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Registered: 10th Sep 03
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Rev counters usually take their signal from the ground point of the coil pack - that's where the famous pea green wire comes from on the Corsa.
You could in theory make up a rev counter/shift light arrangement by wrapping some copper wire around the outside of your HT lead to get your frequency, then it can go to your frequency to voltage IC.
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ed
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(I should say that I do know that on a lot of cars now the rev count comes from engine sensors and the ECU before the pedant police turn up)
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Steve
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if i stick a multimeter on one of the rev counter wires what am i looking for? a pulsating reading?
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Rob_Quads
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What are you using this to drive? This circuit is probably only suitable for low current devices.
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ed
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You'd need an oscilloscope really. A multimeter will be too slow and doesn't have very high resolution.
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Steve
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i dont have an ocsilloscope lol.
hmm if i could work out where to get that input id be sorted
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oceansoul
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quote:
Originally posted by Steve
if i stick a multimeter on one of the rev counter wires what am i looking for? a pulsating reading?
Na, you'll be needing to measure the frequency which i doubt your multimeter could update fast enough. Ideally you want to use an oscilloscope.
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Steve
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thinking about it doesn the cigarette lighters voltage pulse?
eg. how do them sound devices generate sound to match your revs from the cigarette lighter?
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oceansoul
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quote:
Originally posted by oceansoul
quote:
Originally posted by Steve
if i stick a multimeter on one of the rev counter wires what am i looking for? a pulsating reading?
Na, you'll be needing to measure the frequency which i doubt your multimeter could update fast enough. Ideally you want to use an oscilloscope.
EDIT: Too slow.
I guess the 3 wires will be the 12V LT side into the dispak, the earth, and the 3rd MIGHT be a signal from the ECU when to fire hmm idk actually.
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ed
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quote:
Originally posted by Rob_Quads
What are you using this to drive? This circuit is probably only suitable for low current devices.
Could drive anything though as you could use an LED straight off of it or any number of things with a suitable transistor or relay.
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ed
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Does your car not already have a rev counter though?
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Steve
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yes im messing about making a sequential led shift light, the parts are only a few quid and i reckon i might be able to sell a few as the ones you buy cheapest is like 90 quid
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Steve
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quote:
Originally posted by oceansoul
quote:
Originally posted by oceansoul
quote:
Originally posted by Steve
if i stick a multimeter on one of the rev counter wires what am i looking for? a pulsating reading?
Na, you'll be needing to measure the frequency which i doubt your multimeter could update fast enough. Ideally you want to use an oscilloscope.
EDIT: Too slow.
I guess the 3 wires will be the 12V LT side into the dispak, the earth, and the 3rd MIGHT be a signal from the ECU when to fire hmm idk actually.
in that case couldnt i just take a point from the 12v LT wire? how would i determine which that wire is?
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oceansoul
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Possibly. Im not too sure how a dispak works though. If inside it is the same setup as a coil and points etc then that might work. However i have a feeling it's all sold state decives and may not work the same way.
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Steve
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ok, well back to the cigarette lighter, how do them sound generators alter the sound based on your revs purely from the lighter socket? surely the voltage must pulse there too?
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