Wireless ignition kill switch for the NSX

[BryanZublin]

I am considering designing a wireless ignition kill switch for the NSX and I would like to hear opinions from NSX owners before I get too far along. The product would work like this:

1. Small box installs in the NSX in series with the circuit to be disabled. This can be the starter motor or fuel pump. The unit will be designed to handle at least 20 amps of current, so no extra relay would be required.

2. The unit will be designed to work with the existing NSX key fob (transmitter), so no additional transmitter needs to be carried. The unit will "learn" the code of the transmitter during the installation.

3. When starting the NSX, the user will have to push the "unlock" button on the transmitter. The unit will then "unlock" and apply power to the starter or fuel pump and the car will start. The unit will remain "unlocked" as long as the ignition is on.

4. The unit will "lock" automatically when the ignition is turned off and will not draw any power from the battery when the iginition is off.

My goal is a simple design that is easy to use and adds an extra level of security on top of the existing NSX stock alarm system. My retail price target is $50 to $100.

 

[nsxhk]

Bryan,

Will it work with aftermarket alarm system? I don't have the oem wireless door opener.

Henry.

 

[Sig]

Bryan-

I would buy one today if it were available.

Will there be an option available to those that do not have the OEM transmitter? I have neither an aftermarket alarm or the OEM wireless key transmitter.

Good luck.

 

[matteni]

Sign me up!

Me too Bryan. Great idea and should go nicely with my smart shift, smart TCS, and SmartTenna!

 

[ANYTIME]

Where do I sign up?

 

[Jerry Ferdinand]

sign me up as well

 

[BryanZublin]

Thanks for the feedback. My plan was to first design the receiver only to work with the existing transmitter from the NSX. Then I could design a transmitter for those who currently do not have keyless entry (and could install it in any vehicle). The receiver could also be modified to work with other vehicles transmitters and other aftermarket alarms depending on the demand.

 

[DonDavis]

not to sound sarcastic

or be a smart-a**, but couldn't you do the same thing with any basic alarm system that has a tx/rx and a 20-amp relay in it? I mean, you schlep to Wal-Mart, but the $50 special, install it in series with your ignition or fuel pump and viola`?

(Aside from the fact that yours will recognize and learn the NSX transmitter codes, obviously.)

Don

 

[Kinan]

What kind of failsafe mechanism are you planning say for when the receiver front end gets saturated/interfered with or the transmitter fob quits working?

Either of these would strand the car.

 

[BryanZublin]

Originally posted by Kinan What kind of failsafe mechanism are you planning say for when the receiver front end gets saturated/interfered with or the transmitter fob quits working? Either of these would strand the car.

"Fail safe" to me means that you will be able to start your car in the event that the electronics in the receiver unit fail. This is commonly accomplished by using a "normally closed" relay so that if the failure mechanism is loss of power to the relay, the start circuit will still be completed. However, if the failure mechanism is that the relay is always powered, then you are still stranded. No system is perfect. In my opinion, this "fail safe" method has a significant security flaw: simple cutting the power wire to the alarm unit will allow the engine to be started.

Regarding receiver interference, there are a few scenarios:

1. Interfering signal at low signal level at same frequency.
This is solved by the intended transmitter level being higher than the interfering signal level. My design assumes you are transmitting inside the cabin when starting the car, with a transmitter to receiver distance of 10 feet or less, so the signal level will be much higher compared to the interference signal level.

2. Interfering signal at high signal level at same frequency.
In this case, the received interference level exceeds the attenuation range of the automatic gain control (AGC) and the receiver front end saturates. The receiver will not be able to receive a valid signal. There is no "fail safe" solution to this scenario. It would require the user to take action to bypass the unit. This is the case for any aftermarket security system with ignition kill. The probability of this occurring is very low because the frequency bands and power levels for keyless entry are well defined and regulated by the FCC.

3. Interfering signal at varying signal levels at different frequency.
Whether or not this will cause receiver problems depends on the interfering frequency offset, relative signal level, receiver selectivity, receiver image rejection, and receiver front end distortion performance. If reception was impaired, the solution would be the same as case 2 (ie. there is no "fail safe" solution).

A transmitter with a dead battery or losing your transmitter has nothing to do with the receiver failing. There is no "fail safe" solution.

 

[Kinan]

Please forgive my ignorance.

So, if I drive to the top of Mt. Soledad and the receiver captures some high level spurious signal or is desensitized by some off freq high level signal, I'm calling a tow truck?

Or is there some other scenario I'm missing?

Your design sounds like a good idea but is only as good as long as it works properly.

So by failsafe, I mean if it fails am I safe?
Can I still start my car?

 

[BryanZublin]

Originally posted by Kinan So, if I drive to the top of Mt. Soledad and the receiver captures some high level spurious signal or is desensitized by some off freq high level signal, I'm calling a tow truck?

Assuming that you know where the unit is installed in your NSX, you would have to electrically bypass it. This is the case with any aftermarket solution.

Since you mention Mt. Soledad, have you experienced interference there in the past?

 

[CokerRat]

What's your approximate timeline for being able to produce it and make it available for sale? (We're a pushy bunch, aren't we?!)

 

[Kinan]

I would hope most aftermarket designs have tested for this scenario. What is the standard automotive RFI spec, something like 100 V/Meter for conducted emissions 10 KHZ to 2 Ghz? Its been a while...

I mentioned Mt Soledad because there are a lot of transmitters up there from many different sources, the worst field strength being 94.1 FM which is 100 KW CW (not ERP); unless there is TV there in which case it would easily be double that and it is easy drive to get there.

When I hiked to the top of Mt. Woodson, my cell phone indicating full RSSI wouldn't make a call.

Front end desensed from too much junk in the air there.

 

[BryanZublin]

Kinan,
Electronic products are tested for conducted susceptibility and radiated susceptibility (as well as conducted emissions and radiated emissions).

Conducted susceptibility refers to a product's ability to function when there is interference present on the wires to the device. For example, noise on the power wire caused by motors, switching power supplies, transient load changes, etc. This is typically lower frequency interference and is easily filtered by the product (60 Hz to 1 MHz).

Radiated susceptibility refers to a product's ability to function when there is interference present in the air. This is tested over a wide frequency range. Dealing with this type of interference is harder and requires shielding in addition to filtering.

As I mentioned previously, interference at the same frequency as the transmitter can not be "filtered out" so there is no solution. The probability of this occuring is low as I mentioned below because of FCC regulations.

A much more common occurrence, as you mention, is a large signal at a different frequency (TV or radio transmitter). Since I am still in the design phase, I will consider this and choose what I believe will be sufficient rejection of unwanted signals. Since I am local to Mt. Soledad, I can easily test my design there. However, please understand that any design can be made to fail if the interference is large enough.