Wireless Auto Unlock Key Fob??

Wireless & IoT
1

Hello Everybody!

Let me start off by saying I am an extreme embedded electronics novice. This site was actually recommended to me by a member over at mp3car.com, due to my question there.

I do not know where to start and I hope y’all will be willing to provide some advice/suggestions.

I am looking to make a device that does the following:

Have a small transmitter (will be referred to as “fob” from hereafter) that upon getting within 10ft of the car allows the successful usage of a switch hidden underneath each door handle that gives power to the door lock solenoids.

So to get in the car, you would walk up to it and push a button (located on the underside of the door handle) that unlocks the doors, this would trigger the door lock solenoid and unlock the doors, you would pull the handle.

If Joe Blow though walks up to the car (when I am not within range) and pushes the button it would do nothing.

Also, I would like this transmitter to activate what I would imagine would be a “constant” relay to allow me to start the car via a push button switch. So as long as the fob is within distance the car can be started without a key, but via a switch. (the starter button stuff has already been figured out, it’s just what would be needed to make sure it is only operational when the fob is within range)

Lastly, I would like the doors to automatically lock once the fob has left range.

The car all this is going on is a Honda s2000 and I am trying to loosely emulate the car key fob systems of Mercedes Benz, Infinity, Lexus, etc. Although I’m not looking for an “alarm” solution so much as just a transmitter that allows me to push a button to unlock doors.

I’m assuming there is quite a bit of work involved in all of this, but any and ALL advice that y’all can provide would be very very much appreciated!!!

2

w00tw00t111:
Lastly, I would like the doors to automatically lock once the fob has left range.

The transmitter would have to continuously transmit, all the time. When the receiver picks up the right signal from the transmitter, then the doors would automatically unlock, or lock when there is no signal, is this correct?

I think there are laws (FCC) for transmitting continuously, I am not sure. I think it is 1 second max or something similar.

The transmitter can send an unlock code every few seconds, but the batteries would not last very long at this rate.

3

newbie123:

w00tw00t111:
Lastly, I would like the doors to automatically lock once the fob has left range.

The transmitter would have to continuously transmit, all the time. When the receiver picks up the right signal from the transmitter, then the doors would automatically unlock, or lock when there is no signal, is this correct?

I think there are laws (FCC) for transmitting continuously, I am not sure. I think it is 1 second max or something similar.

The transmitter can send an unlock code every few seconds, but the batteries would not last very long at this rate.

You could use an active ping/response from the car so you don thave to continually transmit.

4

That’s what I was thinking about earlier today (the fact that it would always be transmitting). The thought I had is possibly transmitting like every .5seconds? That wouldn’t be nearly as taxing, but would get the job done for sure.

I’m honestly note sure what active ping/response means socoj2 (in regards to electronics - as I’m familiar with the term and syn/ack concept etc.)

I’ve been reading up today on the basics of e.e. and oh my goodness is it facsinating! Still at the complete infancy stages, but it seems as though this is quite do-able.

Also, instead of fm transmitting I’ve been debating using bluetooth. That way the remote would pair with the receiver inside the car and depending on signal strength (which would be indicative of distance) different actions could take place. Also, I’d assume I could add a button or two to the bluetooth fob and program a certain code transmission upon pressing it? (I’m guessing have no honest idea).

Like I said, I’m still researching and learning learning learning.

5

Off the top of my head, I have 2 thoughts on this -

For the transmitter FOB part -

I’m wondering if an RFID tag (either active or passive) might suit your needs better.

A passive RFID tag would always be on, and not consume an power, but would only work if it were very close to the car

However, an active RFID tag, could transmit to a receive at a distance within the range u design.

For the Remote Start feature -

Not to be negative, but I think you will have a VERY hard time trying to create a device from scratch to remotely start the car. Most auto manufacturers keep details about the ignition/ignition interlock system highly guarded; so as not to teach crooks how to hot-wire it.

If this info were widely known - the car model would be easier to steal, therefore get stolen more often. This would increase premiums for the car, and could ultimately negatively impact sales.

So, it is in their best interest to make sure you cannot figure out how to hack those wires under the dash. They may sell an aftermarket remote-start kit, or some third party may have designed one. And you could certainly interface one of these modules into another circuit you are building for the rest of this project.

I hope this was somewhat helpful - didn’t intend to be negative.

6

w00tw00t111:
I’m honestly note sure what active ping/response means socoj2 (in regards to electronics - as I’m familiar with the term and syn/ack concept etc.) .

The device in the car would always send out a request every 10-15-30 seconds. If the Fob is not in range and it doesnt receive a reply from it, the car then goes ok he is out of range.

7

With the 24L01 sold on Sparkfun, you can send out a ping every few seconds with a very low duty cycle. The fob would only wake up, listen, then go back to sleep if it did not get a valid signal from the car. A couple of watch batteries could last a year or more! Range up to 50 feet would be no problem.

8

AZRobbo:
Off the top of my head, I have 2 thoughts on this -

For the transmitter FOB part -

I’m wondering if an RFID tag (either active or passive) might suit your needs better.

A passive RFID tag would always be on, and not consume an power, but would only work if it were very close to the car

However, an active RFID tag, could transmit to a receive at a distance within the range u design.

For the Remote Start feature -

Not to be negative, but I think you will have a VERY hard time trying to create a device from scratch to remotely start the car. Most auto manufacturers keep details about the ignition/ignition interlock system highly guarded; so as not to teach crooks how to hot-wire it.

If this info were widely known - the car model would be easier to steal, therefore get stolen more often. This would increase premiums for the car, and could ultimately negatively impact sales.

So, it is in their best interest to make sure you cannot figure out how to hack those wires under the dash. They may sell an aftermarket remote-start kit, or some third party may have designed one. And you could certainly interface one of these modules into another circuit you are building for the rest of this project.

I hope this was somewhat helpful - didn’t intend to be negative.

Thank you guys for the responses!

The RFID is the first method I’ve looked into as I believe passive RFID’s are what most manufactures use (MB, Infiniti, etc.)

With the active RFID, is it possible to do different actions within certain ranges?

For instance, one of the actions I was looking at taking with the Bluetooth method was when I was within 20yd of the car and it was dark (night/dusk) to turn on puddle lights, running lights, and cabin lights.

Then once I was within 5yds, unlock the car.

Is something like that possible? (Staging of events based on range)

In regards to the auto-start, I’m totally with you on that! Also, I’m a fairly big fan of use what’s available to you instead of re-inventing the wheel…unless there isn’t a wheel available for you :stuck_out_tongue: So, I was going to install a viper alarm with remote start, but instead of using the provided key fob I would be using my custom RFID/Bluetooth/etc fob to unlock the car/disengage the alarm and if possible have a button that sent a signal to the receiver to auto start the car.

The biggest and most important thing to me right now though, is just auto unlocking/disengaging the alarm (essentially one in the same as the alarms brain would be what was getting the voltage and it would be passed along as though the “unlock (and disengage)” button was pressed.

Ronny & socoj I’ll have to do more research on the ping 2.4ghz rf method. Is it possible to do the staging of events like mentioned above? (I’m assuming you could extend the range of the receiver by attaching an antenna to the 24L01?)

9

Ronny & socoj I’ll have to do more research on the ping 2.4ghz rf method. Is it possible to do the staging of events like mentioned above? (I’m assuming you could extend the range of the receiver by attaching an antenna to the 24L01?)

Easiest way would be build in a delay. based on range would be difficult. but the staging of stuff not very hard.

10

Range based measurement is a little iffy. Even at 2.4 where it is line of sight, there are lots of factors to take into account. Not the least of which is Wifi interference or the nanny cam on the bumper of the car next to you (I don’t know why, he just has one!). But, you can get it to work. It is a pretty advanced application though, and one heck of a challenge. I’d stary with two nRF24L01 break out boards and go from there…

11

Yeah, I mean technically the ultra accuracy of range is not super important. It would really be more of a convenience factor then anything else.

A photoresister is what would be needed to detect light right? So that could just be tied into all of this to sense if it was dark - and if it was turn on the lights and that way by the time I get to the car the lights are already on.

I guess truthfully, since I’m just getting started I’m wanting to get the “passive” entry working first and foremost and then just make sure that whatever solution I use for that is expandable so that when I learn more I can add more features (like the light thing etc.)

For a novice is bluetooth connectivity honestly probably to advanced?