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I'm making a remote starter for a car using a Raspberry Pi. The problem is that the car has a manual transmission. The driver needs to remember to place the gear shift in neutral when parking, otherwise all kinds of bad stuff could happen when the car is started in-gear.

What possible solutions do I have for making an interlock that prevents the car from starting in gear? It's a 2001 Honda Accord, if that helps. I have seen transmissions with sensors (switches) on every gear, but this transmission does not have those. I thought of monitoring the speedometer sensor, but I think that info would come too late. I'm thinking I might have to put one or more switches on the shift lever to detect its position, but this sounds like a lot of work.

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    $\begingroup$ Does the car not have an internal system that you can hijack for this purpose? My stick-shift won't even attempt to start if I turn the key without the clutch depressed, for instance. $\endgroup$ – Chris Mueller Oct 19 '15 at 13:09
  • $\begingroup$ Yeah, there's a safety switch on the clutch pedal, but it will have to be disabled because nobody will be in the car to press on the clutch. $\endgroup$ – Carlton Oct 19 '15 at 13:10
  • $\begingroup$ Or move that switch to the stick so it's only active (reads clutch depressed) when in neutral $\endgroup$ – ratchet freak Oct 19 '15 at 13:11
  • $\begingroup$ @ratchetfreak, That's kind of where I'm going at the moment; the problem is that I can't figure out an easy way to detect the position of the shift lever. When I take the cover off the shift lever again I'll take pictures to post; maybe someone can think of an easier way to mount a switch. $\endgroup$ – Carlton Oct 19 '15 at 13:18
  • $\begingroup$ I'd use sensors, but: Briefly apply a controlled current or energy burst that is enough to turn the engine over unloaded but not enough to move the car when in gear and observe results. Current control is hard. Timed pulse is easier but more risky. $\endgroup$ – Russell McMahon Oct 22 '15 at 1:54
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I can't think of a more elegant way than adding a sensor or sensors either.

An inductive sensor may be a good option for a switch if you have enough room below and the stick has metal in it. If not, you could epoxy a magnet to the hidden part of the shifting stick and use a hall effect sensor (or reed switch but I don't recommend it). A roller style limit switch may also be an option, but I would recommend going non-contact if possible. http://www.amazon.com/gp/product/B008MU1GEY http://www.mouser.com/ProductDetail/Littelfuse/55100-3H-02-A/?qs=nyo4TFax6Nff4PypTg%2FOjg%3D%3D

You may also want to include the parking break in the interlock system. It would be a little insurance if the sensor fails.

An accelerometer would also be some good insurance. If it feels a kick when it starts the engine it immediately stops and prevents further input until the car is manually started. Even though this response will be very fast, the car could still creep forward 6 inches or more so it would still be a safety issue and couldn't be the primary interlock system.

And as previously mentioned in the comments you will want to make sure that if you are bypassing the clutch interlock you make sure that it is still enforced when starting the car manually.

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  • $\begingroup$ I never thought of an inductive switch, that may be what I need. $\endgroup$ – Carlton Oct 19 '15 at 23:24
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Your car has a safety switch to avoid starting in gear with the clutch engaged. Use it. Running the start signal through the park brake switch is also a good idea since it will be on if parked in neutral, and should always be used.

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    $\begingroup$ The clutch switch doesn't help me in this case. It will have to be permanently disabled because the clutch will always be engaged when I want to remote-start the car. That's why I need to detect whether or not the transmission is in gear. $\endgroup$ – Carlton Mar 1 '16 at 13:33

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