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Old Sep 08, 2011, 03:23 PM
Dave the Rave
dmccormick001's Avatar
Joined Jun 2007
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New Project - An Opto-isolated Kill Switch

Hey Guys!

I'm thinking about starting a new PIC project, an opto-isolated kill switch for use with CDI-equipped gas engines. I know there are several RTF units on the market, but I'd like to build my own. I learn a lot by stumbling my way through the programming.

I'm planning to use a 12F675/629, and I'd like to hear from the experts here about what features you think should be included, and maybe some things I should be careful of. And of course, I'm sure I'll need some help with everything from the circuit design to programming. Here's my list of features so far:
  1. Input voltage from 3 to 24 volts
  2. Shut down if no signal present
  3. Switchable from transmitter
  4. Remote LED to indicate ignition is "hot"
  5. Opto-isolated to prevent RFI

One of my first questions is this: how long should the program look for a signal before deciding that there's a problem and killling the ignition? I don't want it to be too sensitive and mistake a slight glitch as a loss of signal.

Any other input would be great. And feel free to sling some code at me if you just get a "hankering". (Let's see Alain translate THAT word! )
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Old Sep 09, 2011, 12:31 PM
"MAYONNAISE"
Acetronics's Avatar
Le Treport, France
Joined Jun 2004
1,414 Posts
Hi, Dave ...

" The Gas Brain " already existing for 5 or 6 years ... ( 06/2005 )
Alain
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Old Sep 09, 2011, 12:53 PM
York Electronics
Gary Warner's Avatar
Dallas Tx USA
Joined Apr 1999
2,505 Posts
Quote:
Originally Posted by dmccormick001 View Post
Hey Guys!
One of my first questions is this: how long should the program look for a signal before deciding that there's a problem and killling the ignition? I don't want it to be too sensitive and mistake a slight glitch as a loss of signal.
You can add a programing mode that will let you change the delay for lost signal conditions. I'd consider using a tact switch and an LED and something like holding the switch down when power is applied to enter the programming mode. Once in it, say for example, it would blink once for every second of delay. 3 blinks would be 3 seconds, etc.. Pressing the switch would change the delay and the new delay would be indicated in the blinks. You can use the EEPROM on the PIC to store/retrieve the delay value. What might be more of a practical delay would be Tenths of a second and the associate blinks.

Also the code logic might shut down the engine for 'X' number of missing frames, excessive changes (say a frame is more than 20% different from the previous frame) and a condition that allows for restarting the CDI if a short time passes (a second or so) and then good frames are re-established, but once a limit was crossed with bad or missing frames (say several more seconds) the shutdown would be 'latched' and stay in place until a reset (cycle remote power) condition occurred.
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Old Sep 09, 2011, 03:41 PM
Dave the Rave
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Joined Jun 2007
876 Posts
Quote:
Originally Posted by Gary Warner View Post
You can add a programing mode that will let you change the delay for lost signal conditions. I'd consider using a tact switch and an LED and something like holding the switch down when power is applied to enter the programming mode. Once in it, say for example, it would blink once for every second of delay. 3 blinks would be 3 seconds, etc.. Pressing the switch would change the delay and the new delay would be indicated in the blinks. You can use the EEPROM on the PIC to store/retrieve the delay value. What might be more of a practical delay would be Tenths of a second and the associate blinks.

Also the code logic might shut down the engine for 'X' number of missing frames, excessive changes (say a frame is more than 20% different from the previous frame) and a condition that allows for restarting the CDI if a short time passes (a second or so) and then good frames are re-established, but once a limit was crossed with bad or missing frames (say several more seconds) the shutdown would be 'latched' and stay in place until a reset (cycle remote power) condition occurred.
That will be fun to work on. Thanks for the ideas!

I could use pre-set delays, like maybe .25, .50, and .075 seconds, and have the program jump to a different variable depending on how many times the switch is pressed after it enters the programming mode.

The only thing I'm not sure about would be the idea of allowing the engine's CDI to be re-started. I'd be afraid that as it freewheeled it might flood the cylinder, maybe cause it to backfire and possibly start running backwards. That would be an interesting development, to put it mildly. I'll have to ponder that idea a bit.
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Old Sep 09, 2011, 05:02 PM
York Electronics
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Dallas Tx USA
Joined Apr 1999
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Take what you want, leave the rest. It's just an "idea".
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