When I first went out and bought a remote start for my manual vehicle I immediately began wondering how I was going to handle the issue of the clutch interlock sensor (CIS). I figured tons of people must have run into this issue so there had to be some good DIY info, I was wrong.  So here I am sharing what I learned and hopefully putting you on the path to a safer and smarter remote start.


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For those of you who don’t know, a manual car makes you have the clutch engaged in order to start the vehicle. In order to install a remote start you either have to tap into the wires and permanently short them (which can be dangerous if the remote start is accidently pressed while the vehicle is in gear) or attempt a DIY neutral safety switch (NSS).

The easiest way for me to determine if the car is in neutral is by the position of the shift lever.  First thing that came to mind in detecting what gear the car was in would be to create an array of light emitter/phototransistor around the neutral position. If any beam was broken I could assume the car was in gear. Wanting to minimize the risk of ambient light along with preventing my center console from glowing at night, I chose to use Infrared emitters and detectors.


The rough sketch above was my initial concept. Technically you only need the horizontal beams to determine if the car is in gear, but I will be using this same sensor in a future project where I need to know which gear the car is in. (Stay tuned for that!)

The circuit for the controller is below and was the first part of this build. I wanted to make this as simple as possible so my first goal was no voltage regulation. To do this I needed to find a quad AND gate that would take at least 14.4v. If you decide to make a two beam version of this sensor you can go to a single and gate chip, but you also need to make sure the one you pick can source enough current for the optical relay. Many of these devices are just meant for logic so sourcing more than 2ma can damage them. Note: In my final design I changed R1-R4 to 4.7KOhn and the LED current limiting resistor from 125 to 270Ohm as the phototransistors saturated when the infrared LEDs were at ~16mah.

Board Layout Pictures:

I believe the connectors are JST - EHR series, but I could be wrong. The proto board I have use have 5 holes per row, so I cut the traces to allow for a smaller final board size. The 3 Pin connector is power, 2 pin is to the clutch interlock wires, and the 6 pin goes to the sensor we will build soon!

Here is the potted final Product

Sensor Build:

There are numerous ways that one could mount the array, but I wanted something that could be easily removed and would not permanently alter the car. So off I want to my local hardware store for ideas where I found this:

It's a 3” to 2” adaptor for PVC pipes and  after thinning out the interior wall with a hobby knife would slip right over the boot of the gearshift.

For my first attempt at mounting the infrared emitters/detectors I decided to keep it simple and drilled holes in the rubber mount which the emitters/detectors could be pushed into. I made sure that I made all the lines and measurements while the mount was on the car as the boot was oval shaped and deformed the rubber.

First Attempt


This first attempt did okay, but it look many tries to get everything mounted correctly. The biggest issues is illustrated below. The Holes for the emitters were not going in parallel to the rubber, so when I inserted the infrared LED the rubber would cause it to rotate slightly. Due to the very narrow beam width this would cause the emitted beam to miss the detector entirely. I then tried drilling to predict the rotation and assume to rubber would push the sensor back a few degrees, which did work better. In the end, this design did work, but it was touchy and not something I felt would endure. On the plus side, if it failed it failed safely and the car would only not auto start (which is good).

So on to the second revision, and a revisitation of my childhood!

What I needed to make this next revision a success was a platform that was both versatile and ridged, and then it hit me, my erector set!

I made a rig that would allow me to epoxy the emitters/phototransistors to the std pieces and off I went. I took many more pictures of this design in progress so I will let them do the talking.


Some Notes: I did go through and put a dab of epoxy on each bolt to make sure nothing would shake loose over time. I also decided to use the metal frame as my ground wire.

Installation pictures and test!