Lesson 7 -----------------------------------------------------

The computer board is in. Here are a couple of pictures. Tiny
computer board. Also what the software writing program screen looks like.

Initial proposed ignition software strategy is: Start a 16 bit counter with
input from an oscillator (say 10,000 hertz or cycles per second) when the
e-shaft trigger pulses. Stop the counter when it pulses again.
Read the number in the counter and restart the counter.

That number will be inversely proportional to the RPM.
Big number low RPM. Small number high RPM. Divide the number
by 360 and that result will be the number of counts per degree
of e-shaft rotation. Use that number to fire the plugs
at 20 degrees BTDC and once every 10 degrees there after for
five or six times. Thats it. That is all the program has to
do.

I had a talk with Klaus about it and he has been selling something
like this msd CD system for ten  years. He suggesting firing them one right
after another but his experience is with piston engines and
not rotaries. He did suggest to let the engine turn over a couple
of times to let the capacitors fully charge before using
them to fire the plugs as getting a hot spark for starting always
seems to be a problem with mag type systems.

BTW the current drain by this computer board is so low it can be powered
off the 300 volt outboard motor alternator mounted on the e-shaft
through a voltage divider. No battery required. As long as the prop
is turning you will have power for the ignition computer.


Lesson 9 ---------------------------------------------------

I had some additional thoughts on the software strategy above.
The counter number is proportional to 360 degrees so dividing by 2
will give us the 180 degree e-shaft position for firing
rotor 2. That eliminates one crank angle sensor pick up.
The one we have left will indicate 22 degrees or more
BTDC for rotor one firing. There is aways a trade off of
hardware verses software in these small embedded control
computer systems.

BTW One of the neat things about this chip
is it has a hardware real time clock that is updated every
.001 second (one millisecond). You can read the clock
at anytime and tell what time it is to the nearest .001 second.
That will come in handy.

One of the things I don't like about it however is it has only
one external hardware interrupts. I had eight back in 1975 in my
6502 control computer design.

That is why I designed the hardware priority interrupt structure
in the SuperKim. If an external event (a rising edge of a pulse)
came along that needed instant response it set one of eight latches.
These latches were connected to a priority encoder. The encoder would
then signal the interrupt request pin (IRQ) on the 6502. The 6502 would
stop what it was doing and read the priority encoder 3 bit code to
find out which of the eight latches was requiring service. The 6502
would then reset the latch allowing another event to set it again.
This part of the code took about 20 or 30 instructions and happened
in 20 or 30 micro seconds. The one MegaHertz 6502 then processed the
request. Consequently the SuperKim could take in data, update a data
LCD display and print the data all at the same time.

This was in 1975!!!! :)

I wonder when the single chip designers are going to wake up to a
feature like this.

For example if I wanted to have two crank angle sensor 180 degrees
apart for rotor one and rotor two I could tell which rotor needed
to fire its spark plugs or inject its fuel without going through a
bunch of software machinations. Since the 68xx I am using and
others CPU's do not have this feature me, Tracy, Mazda and the rest
of the automotive world  all have to figure out when to fire rotor
two in software :)


Paul Lamar