Ignition Timing Questions
08-08-2005 | 07:13 AM
#26
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From: Treasure Island,
FL
RE: Ignition Timing Questions
"The hall switch generates a square wave. When the magnet approches it arms, goes high. It triggers when the magnet leaves, goes low. The duration of the square wave is the dwell time.."
agreed, but the magnetic field shape is not a square wave, so the distance from the magnet to the sensor will, at some point, begin to affect the width of the pulse....
"If I understood Terry correctly in one of his other posts, the system only uses dwell timing for starting (up to 800(??)RPM), and then reverts to measuring between hall pulses (much more accurate). "
clever.... this makes my concerns about your dwell-approach much less important...
[:-]
agreed, but the magnetic field shape is not a square wave, so the distance from the magnet to the sensor will, at some point, begin to affect the width of the pulse....
"If I understood Terry correctly in one of his other posts, the system only uses dwell timing for starting (up to 800(??)RPM), and then reverts to measuring between hall pulses (much more accurate). "
clever.... this makes my concerns about your dwell-approach much less important...
[:-]
08-08-2005 | 09:38 AM
#27
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From: Riverton,
WY
RE: Ignition Timing Questions
ORIGINAL: FenceMagnet
"The hall switch generates a square wave. When the magnet approches it arms, goes high. It triggers when the magnet leaves, goes low. The duration of the square wave is the dwell time.."
agreed, but the magnetic field shape is not a square wave, so the distance from the magnet to the sensor will, at some point, begin to affect the width of the pulse....
"[:-]
"The hall switch generates a square wave. When the magnet approches it arms, goes high. It triggers when the magnet leaves, goes low. The duration of the square wave is the dwell time.."
agreed, but the magnetic field shape is not a square wave, so the distance from the magnet to the sensor will, at some point, begin to affect the width of the pulse....
"[:-]
08-17-2005 | 06:22 PM
#28
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From: Penrose,
CO
RE: Ignition Timing Questions
Interesting question and discussion. I have a home built CDI ignition that is controlled by a MicroChip PIC 16F627. I cannot tell you how CH works, but I can explain my design. To set the Hall sensor/magnet combination I also recommend slowly rotating the prop until the spark fires and adjusting this to occur at 32 deg BTDC.
What is happening in the software is the PIC chip is looking for the Hall sensor signal and when it triggers it measures that it is at X RPM. It then calculates the spark delay time Y for X RPM and starts counting down the prescribed Y microseconds (really scaled computer cycles to be exact). Since all this is happening very fast and you are rotating the prop very slowly the observed spark is almost instantaneous despite the fact that the PIC might be thinking the RPM is much higher and the delay should be 12 deg BTDC.
To see more of my PIC/CDI module go to http://home.earthlink.net/~marlowedc/CDI.htm
What is happening in the software is the PIC chip is looking for the Hall sensor signal and when it triggers it measures that it is at X RPM. It then calculates the spark delay time Y for X RPM and starts counting down the prescribed Y microseconds (really scaled computer cycles to be exact). Since all this is happening very fast and you are rotating the prop very slowly the observed spark is almost instantaneous despite the fact that the PIC might be thinking the RPM is much higher and the delay should be 12 deg BTDC.
To see more of my PIC/CDI module go to http://home.earthlink.net/~marlowedc/CDI.htm
