Newbie making an ignition timer

[ChrisHelvey]

Although it was asked with humor...it's a great question.
After this, I think they'll shut us down because it's off-topic, but...

It has been suggested by many that the survival of a species or social organization will depend on its ability to most efficiently direct available energy into channels favorable to the preservation of the species.

So, this becomes about USEFUL energy transformation.

And then, in my opinion, we should be able to waste as much as we want as long as we don't trash our environment doing so.

So, is ANYTHING really necessary?

Hmmmm.....

[Acetronics2]

Hi, Chris

YES ...

Preserve life !!!

Easy to say ... no so easy to do !!!

Alain

[enauman]

I'm curious if this project ever came to fruition. I'm currently designing an ignition system for a vintage triumph engine for Bonneville Salt Flats. I started out using an AVAGO encoder because it was small and cheap and provided a digital position via SPI. I machined a replacement for the factory "distributor" to mount the encoder. I missed something on the data sheet however. The specs said the encoder was capable of clocking the SPI at 1MHz. Plenty fast enough. However, after fiddling with it I noticed it had a sample rate limitation of 10kHz. You can clock the data out at a bit of 1MHz but you can only sample it at one reading every 100uS. Not fast enough for high RPM. At 8,000 RPM, the device only gives a reading every 4 or 5 degrees (48,000 deg/sec x 100uS = 4.8deg). I wanted to have at least 1 sample for every degree of rotation. So I tried to interpolate between readings. I kept track of 2 successive readings to get the rotational velocity ((current reading-last reading)/(100uS)). When I was within 1 delta reading of the ignition point I used the velocity to extrapolate the actual desired ignition point to fire (turn off) the coil. Nice theory anyway. I couldn't get the code fast enough to make the interpolation within the 80uS remaining after sampling the encoder. So I tried to pick an arbitrary point well enough in advance if the ignition point to give the PIC enough time for the calculations. The problem with that was interpolating the ignition point from a greater distance caused greater error. This was largely because this simple method does not take acceleration into account. I chose to do a steady state interpolation ignoring acceleration figuring that if I was within 4.8 degrees of the desired ignition point, there would be minimal error due to accelleration. However when moving the point of interpolation way in advance there is plenty of time for the rotational velocity to change significantly.

I gave up on the digitizing encoder and switched to a quadrature encoder with an index. The one I plan on using gives 2000 pulses/rev with a zero index. It should be easier to reference the index and count pulses. I'm currently machining the distributor to try it out. If anyone is interested, I can post the results later.

Ed

[enauman]

Oh yeah, I was using a PIC16F1824 at 32 MHz.

[c_moore]

Hi enauman,

I would be curious of how you make out with this. I am trying to do something similar with gas model airplane engines. So far I have some code that works,but I think it could be better.

[enauman]

Hi Charlie,

I have a couple of questions for you. What type of encoder are you using? Are you planning on making the advance dynamic or static? Didi you do your coding in PIC basic or assembly? Would you be willing to share your code with me? My interest is purely academic and not commercial.

Ed

[ChrisHelvey]

Hello Enauman,

No, I never finished this project and it was a simple Magneto type lawn mower engine. The necessary inputs for an engine with dynamically changing loads and speeds would be overwhelming to me AND I found that commercial engine management systems on the market have caught up to the tech and can do just about anything. More expensive, yes, but much less time investment. I am talking about MSD products and their accessories.

In any case, about your code, there was a gentleman on this list who DID successfully create a PIC based ignition system for an airplane (full sized.) It was quite impressive but WAY over my head. Do a search on my threads and I think he posted. I'll see if I can find him.

Good luck with this, I wish you well.

Chris