givemethebighammer
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| posted on 18/11/06 at 10:45 PM |
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Electronic schematics
Has anyone got the electronic schematics for a DIY shift light(s) unit and / or a DIY knock gauge.
I'm looking for stuff to build over the winter since the car has been on the road for nearly two years but it's too wet to drive it most
days.
thanks
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BenB
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| posted on 18/11/06 at 11:12 PM |
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Knock gauge is pretty difficult. They have to be tuned to the engine in question which usually means destroying a few.
Ion sensing is intersting technology and the info can be found at
http://users.tkk.fi/~vvartiov/ion/DIY-Ion-Sensing-2.pdf
DIY shift light is a lot easier. Lots of ways of doing it, all depends on how you want to see the shift setting.
Frequency to voltage with potentiometer input into voltage compatator is nice and easy. Half RPM button press setting is a bit more complicated....
Ben
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MikeRJ
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| posted on 18/11/06 at 11:24 PM |
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It's pretty simple as long as you can fit a knock sensor into the engine block.
http://www.gnttype.org/techarea/projects/projectspage.html
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BenB
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| posted on 19/11/06 at 12:23 AM |
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Making a knock sensor is easy.
Making one that can accurately detect knock and filter out engine noise / valve or cam noises is rather more difficult.
After all, there are lots of 3rd party auto electrics out there but universally applicable knock sensors...... Can't think of any...
I'm not saying that a DIY knock sensor can't be made, or that it's not based upon simple electronics.... But the filtering /
development side of things gets rather complicated...
I'd love a knock sensor for my boosted ST1100 but I may be going ion sense....
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givemethebighammer
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| posted on 19/11/06 at 09:53 AM |
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thanks, there 's a few interesting places to start there.
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BenB
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| posted on 19/11/06 at 02:11 PM |
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The LM2907 datasheet shows a simple shift light schematic. Would need turning into a PCB.
Just because I've got lots of PICs and no LM2907s I'd be tempted to go down the microprocessor route. A simple half RPM push button and
that's about it.
Whatever route you do go down, don't forget that the battery is rarely 12v, so the voltage regs will need to be able to handle whatever the
alternator puts out (up to 15v rarely). Also breakdown vans have a nasty habit of attaching 24v to the battery... So the electronics will either need
to handle or this or have an off/of switch on the side (and you'll obviously have to remember to switch it off if you ever breakdown!!)...
Personally I just wait until I hear the engine bouncing around on the rev limiter 
[Edited on 19/11/06 by BenB]
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MikeRJ
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| posted on 19/11/06 at 09:34 PM |
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Automotive spec 5v regulators (i.e. not 7805!) are fairly cheap and easy to get these days from e.g. NatSemi. Add some some extra transient
protection for a belt and braces solution and load dumps etc. should never be an issue.
The best systems might use DSP etc. to filter out specific knock frequencies, but it's not required to get a useable system. The Megasquirt
uses a simple amplitude based measurement, but uses an RPM table to determine thresholds whih seems to be quite effective.
Single threshold systems can also work reasonably well simply because the sensor output during typical knock events is higher than background noise,
though not so good for detecting the smallest trace of knock.
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tks
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| posted on 20/11/06 at 09:12 AM |
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mhh
That scheme doesn´t cope verywell with the high voltages of the coil..
there is allot of noise on that line!
would use a optocoupler, a zener and a normal diode.
wich enables the optocoupler.
Tks
The above comments are always meant to be from the above persons perspective.
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Syd Bridge
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| posted on 20/11/06 at 09:32 AM |
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I've played about a lot with analogue shift light setups, on the youngsters grass track minis. Used as a revlimiter as well.
You'll find that the 2917 is now more suited to a digital type input. IE square wave. Also, the input of a pair of resistors as a voltage
splitter doesn't quite make it.( All to do with the new RoHS rules, and a change in the makeup of the chips.)
Also, you have to filter out the noise and signal bouncing on the input with a capacitor or two.
The 2917 works, but you've got to put a VERY different input stage into it.
We've done a simple traction controller with this setup as well.
Half rev setup uses a flip-flop stage between the input and 2917( and more chances for problems), so unit runs on half input, but uses full for
setup.
In the end, we could have bought 10 commercial items for what was put into the r&d. But, I learned a lot about electronics on the way.
Cheers,
Syd.
[Edited on 20/11/06 by Syd Bridge]
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tks
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| posted on 21/11/06 at 09:06 AM |
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just like i said
you need to add an optocoupler
wich ouput pullsdown a 10K ohm res. wich is connected to the input.
then the led of the optocoupler needs grounding with a 420Ohm resistor.
JUST copy the complete input stage of megasquirt. Its easy...
Tks
The above comments are always meant to be from the above persons perspective.
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Syd Bridge
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| posted on 21/11/06 at 03:56 PM |
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A point to remember in all of this, ......on the Mini we saw spikes, on the low tension side of the coil, go up to 700~800 volts, using an
oscilloscope.
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