Date: Wed, 03 Apr 2002 20:41:54 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Josef Karthauser <joe@tao.org.uk> Cc: hackers@FreeBSD.ORG Subject: Re: Engine management system under FreeBSD. Message-ID: <74853.1017859314@critter.freebsd.dk> In-Reply-To: Your message of "Wed, 03 Apr 2002 19:34:01 BST." <20020403183401.GA43578@genius.tao.org.uk>
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In message <20020403183401.GA43578@genius.tao.org.uk>, Josef Karthauser writes: >We're not talking too high intervals here, probably the maximum timing >speed is around 13k rpm, so that's still in the ms range of things. > >What I'd like to do is use the printer port to sample timing signals and >to drive the fuel injector solenoid and plug sparks. > >Before I start has anyone any advice that they can share with me, other >than I'm stark raving bonkers. Well, we knew that already :-) I would be somewhat worried about jitter if I were you, I don't know what the jitter sensitivity actually is for an engine, but running at 13kRPM we are talking roughly 4.5msec per turn, so all things considered I would expect that your ignition window is well short of a millisecond, and I wouldn't be surprised if the window inside which you want to adjust might be considerably less than a millisecond wide. Doing that from software practically rules out any high-level. You might consider putting a PIC out there for the actual timing, and having a control interface to it along the lines of "pulse this line move ignition earlier, pulse that one and move ignition later. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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