Ignition pickup help
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Posts: 46,084
I've developed a shift light program for my Formula Ford race car,
which works perfectly on the bench when fed from a frequency
generator, but my biggest problem is getting a clean signal from the
ignition system on the car.
The coil connected to a permanent positve 12v and the ground is
pulsed by the pickup that has replaced the points. I have tried
various metod for interfacing this to the stamp, but analogue
electronics are not really my area. When I look at the signal on my
scope, i can often see a spike embedded in the square wave, which
confuses the stamp and gives erratic readings.
Does anyone have any suggestions for how to clean-up this signal and
present it to the stamp ?
thanks
which works perfectly on the bench when fed from a frequency
generator, but my biggest problem is getting a clean signal from the
ignition system on the car.
The coil connected to a permanent positve 12v and the ground is
pulsed by the pickup that has replaced the points. I have tried
various metod for interfacing this to the stamp, but analogue
electronics are not really my area. When I look at the signal on my
scope, i can often see a spike embedded in the square wave, which
confuses the stamp and gives erratic readings.
Does anyone have any suggestions for how to clean-up this signal and
present it to the stamp ?
thanks
Comments
to build a one'shot circuit based on a 555 timer. It will trigger on an
input, and produce an output of a fixed duration then reset and wait for
another input. It will ignore any inputs during the output. Standard
circuits are in the 555 data sheets. Sometimes you can clean up the signal
enough with a resistor/capacitor filter (low pass) that removes the high
frequency spike and allows the circuit to trigger correctly.
jim
http://www.geocities.com/jimforkin2003/
Original Message
From: wheatenuk [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=S2C1HIOkx9SIUYq4K-FmbinBQUsX9NMMbahieib2LUEjIfN1WfjHIAzazsUQwu-6XqTBhyfda15pMhKz9A]alex.meek@d...[/url
Sent: Monday, February 23, 2004 3:47 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Ignition pickup help
I've developed a shift light program for my Formula Ford race car,
which works perfectly on the bench when fed from a frequency
generator, but my biggest problem is getting a clean signal from the
ignition system on the car.
The coil connected to a permanent positve 12v and the ground is
pulsed by the pickup that has replaced the points. I have tried
various metod for interfacing this to the stamp, but analogue
electronics are not really my area. When I look at the signal on my
scope, i can often see a spike embedded in the square wave, which
confuses the stamp and gives erratic readings.
Does anyone have any suggestions for how to clean-up this signal and
present it to the stamp ?
thanks
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STAMP.
The slow response of most will probably not transfer the spike.
> Does anyone have any suggestions for how to clean-up this signal and
> present it to the stamp ?
> For one, you should have an optocoupler to keep those nasty spikes
away from the STAMP.
> The slow response of most will probably not transfer the spike.
> > Does anyone have any suggestions for how to clean-up this signal
and
> > present it to the stamp ?
I've used an optocoupler on my circuit - not been able to test yet
though! I also have a .pdf file of the MegaSquirt ECU showing their
ignition pickup, can post this, but will need to wait till I get
home...
James
your ignition coil set up is what I envision, you should se a very large
narrow spike when the ground on the coil is "let go." This spike is well over
200
volts. Use this spike into the "diode" side of the opto isolator, and use the
appropriate current limiting resistor. In this way you will get true isolation
and the opto will output only on the "big" spikes and ignore the 12 volts when
the coil is not grouned.
Resistor calculation....if your spike is consistantly 250 volts or more and
you want 10mA through the diode section of the opto, then 250/0.01 is 25k ohms.
A 4n35 opto should do the job....you may need to go to a high speed opto
depending on max rpm and switching time of the opto.....
ken
The coil connected to a permanent positve 12v and the ground is
pulsed by the pickup that has replaced the points. I have tried
various metod for interfacing this to the stamp, but analogue
electronics are not really my area. When I look at the signal on my
scope, i can often see a spike embedded in the square wave, which
confuses the stamp and gives erratic readings.
[noparse][[/noparse]Non-text portions of this message have been removed]
(say 16V or so) with a zener and a series resistor.
Mos.
--
78 KE50, 84 AE86, 90 ST185GrpA, 91 MX83Gr, Sydney, Oz.
On Mon, 23 Feb 2004 smartdim@a... wrote:
> Besides the good 555 idea, another option is to use an opto isolator......If
> your ignition coil set up is what I envision, you should se a very large
> narrow spike when the ground on the coil is "let go." This spike is well over
200
> volts. Use this spike into the "diode" side of the opto isolator, and use the
> appropriate current limiting resistor. In this way you will get true isolation
> and the opto will output only on the "big" spikes and ignore the 12 volts when
> the coil is not grouned.
>
> Resistor calculation....if your spike is consistantly 250 volts or more and
> you want 10mA through the diode section of the opto, then 250/0.01 is 25k
ohms.
>
> A 4n35 opto should do the job....you may need to go to a high speed opto
> depending on max rpm and switching time of the opto.....
>
> ken
>
> The coil connected to a permanent positve 12v and the ground is
> pulsed by the pickup that has replaced the points. I have tried
> various metod for interfacing this to the stamp, but analogue
> electronics are not really my area. When I look at the signal on my
> scope, i can often see a spike embedded in the square wave, which
> confuses the stamp and gives erratic readings.