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# Gear position sensor and display

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## Gear position sensor and display

(OP)
What simple parts can I use (off-the-shelf?) to fabricate a gearbox position sensor? I'm thinking about a sensor circuit that could display the manual gearbox position on an instrument panel-mounted, single digit LED array. I couldn't find any aftermarket products in an internet search except for auto. transmissions.

Thanks
Replies continue below

### RE: Gear position sensor and display

You'd need 3 microswitches I think, to detect the position of the lever in the H pattern, for a 4 speed.

One detects whether it is in the 13 or 24 plane, the other two detects whether it is in R or 34.

Thne you need some logic to sort that lot out. You need a bit more complexity to detect neutral as well.

These days you might find it easier to measure the engine speed and the vehicle speed, and then calculating which gear you are in.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

### RE: Gear position sensor and display

There are IC LED drivers available with BCD input. Simplest is to add a switch for each position (or one switch for forward, one back and one for each lane of the gate), connect the switches through logic gates to convert it to the proper BCD output.
National Semiconductor, among others make them.

### RE: Gear position sensor and display

If the car is <10 years old, there's a fair chance the current gear selection is already on the car's data bus.

But I like Greg's idea of picking off the VSS and tach signals and doing the math.  It's a nice job for something like a PIC.

Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

### RE: Gear position sensor and display

The only issue that I see with the speed/tach calculation is it will never be accurate with the clutch in.  If you need verification you hit the right gate before you let the clutch out, this wouldn't help (I've driven some sloppy manuals).

On the flip side of that coin, it could be a good indicator of engine speed matching when downshifting (think non-synchro trans).  It could help many new class A drivers when they get "lost in the gears."

### RE: Gear position sensor and display

(OP)
Not sure if this changes the parameters of parts needed. Perhaps LCD is a better display.

In addition, my shift control is remote, thus I can mount sensors onto a shift tube between shifter assy. and gearbox.

Does any of this provide a cleaner method of installation? Are IC LCD drivers a different animal than a LED driver?

Thanks

### RE: Gear position sensor and display

LCD and LED drivers are quite different. LED drivers only need to source or sink current. LCD drivers have to supply an AC source. Probably easiest to use a micro-controller or specialized LCD driver chips to supply the signals for a LCD driver. Then you need to decide on reflective, back lit or front lit types.
Unless you can program in assembly you will need a compiler for a micro. Not sure about the PIC devices but there is a free C compiler available for the Atmel chips. Then you need a programmer. Unless you want an education, LEDs are easier to use. Ground the correct inputs with a switch and the number appears.

### RE: Gear position sensor and display

(OP)
Talking with a few friends, elec.-types; although LCDs are more visible in sunlight, an LED control circuit might be easier to assemble, and I think off-the-shelf parts are readily available for that part.

I've been searching on the net for a single-digit LED display. Not just a standalone 7-segment chip (SMD or otherwise), but the entire chip and support circuits, something that's small enough to surface mount on an instrument panel or perhaps separate components connected by unobtrusive harness - something as small as a bicycle computer. Is there such an animal without going to a custom-fabbed piece?

Thanks

### RE: Gear position sensor and display

(OP)
NickE,
Thanks, but these are just the LED chip. I was looking for an existing assembly that includes underlying IC and enclosed in a surface mount housing - something off-the-shelf. Maybe such an animal doesn't exist?

### RE: Gear position sensor and display

There is no driving circut for LED displays. I would use the microswithches as described above. Depending on how the chip is wired (common ground, or common source) would determine the wiring diagram. (IE: when the switches are closed for gear 1 the two vertical segments on the right have their circut completed.) You might need to get a zener diode and make a supply to drop voltage, and maybe put some small capacitors across the switched leads to reduce noise. This w/o the LED's could actually be called an electrical device more than an electronic device.

### RE: Gear position sensor and display

I woul think that in the environment shift linkages operate in, a magnetic proximity switch would serve better. They are sealed from the elements and are available off the shelf.

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