1-wire gear position sensor for cars: Critique my circuit

GameboyRMH · Post by **GameboyRMH** » Tue Aug 06, 2013 2:00 pm

I got this idea after hearing of the very convenient factory sensor on neoraptor's bike. Here's the circuit:

The switches are magnetic and can be triggered by the shifter itself or the levers on a transaxle (so they're mechanically locked out such that only one can be closed at a time). The resistance values here should give a ~0.5v difference in the signal between gears. Looks good?

dimondjack · Post by **dimondjack** » Tue Aug 06, 2013 4:06 pm

Yep, but I think you'll get less than a 0.5v difference per gear. My quick calcs said that you are closer to 0.4v for the first three. You could adjust your resistor values to make it exactly 0.5v if you are interested in that.

That said, you'll be fine with this setup.

GameboyRMH · Post by **GameboyRMH** » Tue Aug 06, 2013 5:37 pm

I'm interested, what resistance value did you use in the calculations?

dimondjack · Post by **dimondjack** » Wed Aug 07, 2013 3:00 pm

I just did the very rough calcs (I did them on paper, didn't get to a second decimal) previously. Here are the full calcs as I see them:

1- 5v - 1.5/16.6*5v = 4.55v
(delta of 0.38v)
2 - 3/18.1*5v = 4.17v
(delta of 0.32v)
3 - 4.5/19.6*5v = 3.85v
(delta of 0.27v)
4 - 6/21.1*5 = 3.58v
(delta of 0.25v)
5 - 7.6/22.7*5 = 3.33v
(delta of 0.2)
Rev - 9/24.1*5 = 3.13v

To solve for the resistances to get you a desired voltage, you can use:

Req. resistance = (15.1*(5-DV))/(DV)

Where DV is your desired voltage.

dimondjack · Post by **dimondjack** » Wed Aug 07, 2013 3:08 pm

I just edited my post; I was doing a shortcut and all of my formulas were for the desired voltage drop. I changed it all to be the voltage you want the system to actually read.

GameboyRMH · Post by **GameboyRMH** » Wed Aug 07, 2013 10:24 pm

Thanks, my electronics experience is mostly digital. My only experience with analog circuits is making power supplies for the digital circuits

Recalculated resistor values:

dimondjack · Post by **dimondjack** » Thu Aug 08, 2013 2:58 pm

Looks good! You should get a nice 0.5v drop for each gear.

Post by **brentp** » Thu Aug 15, 2013 12:30 am

This is great! Could we add this to the wiki?

dimondjack · Post by **dimondjack** » Mon Aug 19, 2013 8:20 pm

Brent,

Are you referring to the sensor information (model, etc), or the information on how to calculate voltages (my replies)?

Post by **brentp** » Mon Aug 19, 2013 8:30 pm

I was referring to the whole thing. Also need to review neoraptor's sensor information.

GameboyRMH · Post by **GameboyRMH** » Mon Oct 21, 2013 6:30 pm

Hey, sorry that I missed your replies! Yes feel free to add this to the wiki.