SparkFun Forums

[whitewolf103187]

Hello, I'm new to the site.

I don't have much experience in digital electronics so please keep it simple. Let me give you some info prior to saying what I want to do. I own a Subaru Impreza WRX with a straight cut dog engagement manual transmission, and with a dog engagement transmission to shift under full throttle you can either slightly lift off the throttle to "unload" the gears in the transmission to allow you to shift and mesh the dog gears together, or you can cut fuel or retard the ignition timing to effectively unload the gears by slowing the engine.

I like things automatic, so I'm looking at doing the latter. Problem is, I don't know much about proximity sensors, photoelectric sensors, hall effect or anything else similar to these. I'm basically looking at attaching 2 or more sensors so that when the gear lever is in gear it will either allow a signal through it or block a signal through it but when the lever is pulled slightly it will do the opposite. I need something that g-forces won't affect and that will be able to function anywhere in the range of -40F to 140F since it will be on the inside of the vehicle. Another thing, I'm willing to use a pressure sensor or something similar to a strain gauge if at all possible since it may work better than any sort of proximity/photo/laser type sensor.



Any help would be greatly appreciated!

[lyndon]

Does the shifter go straight down into the transmission or is there a cable/linkage between them? If it's the latter, then you could possibly modify the front/back linkage with a strain gage to detect the force. I have other ideas, but vibration would render them useless.

[AndyC_772]

Skipping ahead a little: When you have your sensor installed, do you know what you'll be doing with the output? Does your ECU have a suitable input for this purpose, or would you also need to modify the ignition timing output? (No point installing sensors if there's nowhere to connect the output!)

Do you need to unload the gears in order to shift out of gear, or only to engage a different one?

[Polux rsv]

I installed and use myself some aftermarket ECU ( Motec, Pectel,...)
Strain gauge is the way to go. It is used everywhere in the race world. It will detect when a force is applied to the shift lever. The electronics could be as simple as a comparator which outputs a "1" when the force reach a predefined level. This level should be set with a potentiometer as each gearbox is different.
Other sensors, like mechanical switch, could be used.

Then you should cut torque from the motor. The simplest and safest way is to cut power supply to the ignition coils. Cuting fuel to a turbo motor could cause serious damage due to overheat in the combustion chambers, and to the turbo also.
Simply insert a P-FET to the 12V powering the coils.

The 12V cut duration should be a constant value, triggered by the force level detector. On motorbikes, I use 40 to 60ms cut. This value depends on your gearbox.

The simplest shifter would be composed by a comparator triggering a LM555 as a monostable, which drives the p-fet. A potentiometer will allow to define the force level needed to activate the shift. A second potentiometer will set the pulse duration.

Angelo

[fll-freak]

Yikes. My safety alarm is rigging on overtime right now. Not that this could not be done safely with the right people and months of testing over large environmental conditions. But this comment: "I don't have much experience in digital electronics so please keep it simple." scares the you-know-what out of me.

[lyndon]

Normally it would me too, but car guys are generally pretty resourceful. In my off-roading days, we'd have to figure out issues modifying engines & powertrain, electrical systems, suspensions, etc. often having absolutely no previous experience and having to make sure a vehicle couldn't get stranded somewhere a tow-truck would never be able to get to.

Caution is needed, but IME, they type of people attracted to working on performance vehicles are resourceful enough to get the job done properly.

[lyndon]

ps, congratulations on your post #1000. Now be sure you don't do anything to spoil that perfect number

[whitewolf103187]

-Shifter has linkages, I've thought about using these but I'd rather keep everything inside the car as I do go offroad sometimes.

-I do have a suitable input for my ECU so that is not an issue. Grounded or not grounded while shifting doesn't matter as I can choose to invert the signal or not.

-I have the option to use either fuel or ignition cut and with my stock ecu with this rom it will cut fuel similar to a rotating idle, where it will cut all fuel to one cylinder per engine rotation in a rotating fashion. Such as 1,3,4,2,1,3,4,2 and so on.

-Unloading the gears to drop it out of gear and go into the next gear would be the most beneficial.

- Polux rsv, if you have any more info on strain gauges it would be much appreciated. I would go that way if I had more knowledge. I'd like to build something myself but I can't find much info on the internet about strain gauges in a motorsports application.

-I've installed aftermarket ecu's myself so I know a decent amount about electronics, also an electrician with the air force on f-16s so going a little more in depth is just like another step for me.


I appreciate the info guys.

[whitewolf103187]

I've been thinking of the possibility of using a capacitive touch switch mounted on one side of the shift knob, does anyone know of anything that would easily attach to a shift knob and have open contacts that would allow any sort of touch input (not pressure) to "actuate" the switch?

[fll-freak]

Any metal surface that is isolated from the rest of the car could be used. Perhaps a metal skull shifter knob is in your future? But these have the problem of not working reliably if you wear gloves or have very dry (non conductive) skin.

If you wish to pursue this avenue, you can get development kits for the chips that support capacitive switches. Pretty sure SFE sells one. If not, I know that one of the MSP430 kits has a capacitive touch sensor.

I think your most reliable method would be Hall effect sensors on the linkage. These would not be subject to issues with dust and dirt. But I am no car junky. After many years of effort, I can now reliably find the gas cap on my car.

[whitewolf103187]

I think your most reliable method would be Hall effect sensors on the linkage. These would not be subject to issues with dust and dirt.

I agree with you on the hall effect sensors, problem with them though is I'd need some type of board to output a signal with it
correct?

But I am no car junky. After many years of effort, I can now reliably find the gas cap on my car.

ha ha, I've worked in a couple shops myself and trust me if that's all your issue with cars it's nothing. I've seen cars come in that have never had oil changed in 50 thousand miles.... it basically forms the tar stuff they use to seal up cracks in road surfaces after that long.

[whitewolf103187]

actually looking at the hall sensor here. http://www.sparkfun.com/products/9312

I could just get a couple breadboards and a couple of these and get what i need done.

[fll-freak]

A Hall Effect sensor is little more than a transistor sensitive to a magnetic field. Bring a magnet close and the switch closes, move it away and it opens. You do need to properly bias the bugger with a resistor, but its pretty simple.

The part you pointed to you will not likely want. It is a LATCHED Hall. This means it will SWITCH its status each time a magnetic field is presented. Not as useful in your case as a plain vanilla Hall effect sensor. Strangely, SFE does not sell a plain Hall, but places like Digikey will be happy to sell them to you.

[lyndon]

Just throwing out an idea here. If your shift knob screws into the shifter (i.e., it's not all one unit), and you have access to a machine shop, then you may be able to make another shift knob. But this new knob would be cut in half, and have a strain gage sandwiched between the halves before being glued back together.

In an application like this, using a strain gage is easier because you're not doing a precision measurement of the force. You just need to compare if it's above a certain threshold that indicates the shifter is being pulled or pushed. Come to think of it, if a custom shift knob is being machined, it may be simpler to embed an optical switch and a flat spring inside, so you get a digital on/off response instead of an analog output of a strain gage.

That's a brain dump: hope it makes sense

[whitewolf103187]

Never thought of using a strain gauge like that. Only thing with that is that it would be hard to screw back on since the threads would be slightly off then, I suppose if it was threaded afterwards it would work. Also I'd need some sort of amplifier for the signal, know of anything relatively cheap that would work?

As for the flat spring and optical sensor, can you explain it a little better I'm not quite understanding what you mean.