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  • Author Author: screamingtiger
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A small project idea - Wireless trailer lighting control

screamingtiger

As an RC plane guy, or rather RC jet guy, I need to use a trailer to pull my jets to and fro.  I built my own trailer using a base from Harbor Freight by building a box on top of it with barn doors on both side.  That is a topic all its own but I digress.

 

One of the main issues I have is the wiring harness that connects from my Jeep to my Trailer.  It is constantly getting corroded,so my trailer lights don't work.  The other issue is sometimes I forget to plug it in or it comes unplugged while I am driving.  perhaps a better plug is in order, but this is 2015.  This is the wireless/Bluetooth era!

 

The current control box I have purchased hooks into my light wiring on my jeep, literally spliced in.  It reads the current coming in and outputs the voltage to the trailer lights.

The main issue is that there are only two trailer lights, and these functions as running lights, brake lights, and turn signals!  So the box is connected to my brake lights and turn signals and converts those inputs into the appropriate signals to emulate those functions on 2 lights.

 

What an "easy" task for an Arduino Pro Mini, or rather 2 of them.  One on the jeep as the transmitter (Tx) and the other on the trailer as the receiver (Rx).

The issue of powering the lights on the trailer is easy, some mosfets and an external battery.  Tricky part will be to emulate the brake lights.  What happens is the lights are dimmer when in running mode, and when I hit the brakes they are simply brighter.  Sounds like a job for PWM!

 

 

The issue of reading the lights a bit more complicated.


The Arduino pins have a 100M Ohm resistor in series with them and they can handle a max of 5.5V, but to play it safe I will assume 5V.   This means the pin can sink .05uA, not a lot of current.

 

A car voltage can vary from around 12V to 15V.  I see numbers in the 14V range when running and 12.6 when not running.  While there are ways to use a resistor to drop the voltage, I think a 7805 is probably a good choice to regulate the voltage.  It will still function in the car battery is below 12V and can handle up to 25V.  So each input from the light, which is reading the voltage going to the light when it is on, will go through a 7805.

This will allow the Arduino pro mini to read the lights and process the signals to send out.

 

I'm  open to other ideas but a 7805 seems like a good idea.  I would need about 6 of these.  more to come in the next post!

image

This is an early picture of my trailer, before I straightened out the side beams.  The trailer has advanced quite a bit this stage an in my next post I will show better pictures.

 

 

 


  • Ive been slowly gathering parts of this.  I got some NRF24L01+ 2.4 ghz modules for communication.

    I also picked up some mosfets for another project but after I did some testing on the lights, the running lights pull 500Ma and the brake lights pull nearly 2A, and that is per side.

     

    So I think I am going to resort to physical/mechanical relays.  The ones I have are logic level but can handle 5A.  I will still need 4 relays though as the lights must also function as blinkers.  I am going to the store today to look at an LED based light for my trailer, I am curious how many amps those pull.  I also like the idea of not worrying about burnt bulbs to change out.  I may be able to use the mosfets yet.

     

    I have some Chinese clone arduino mini pros I am going to be using.  I am also considering a control panel with a touch LCD that lets me see what the lights are doing and allows me to manually control them for testing.  For that I many have to use an arduino mega to have enough pins for the LCD but you can get those cheap (~10USD) as well.

     

    Finally I have a small motorcycle battery to power the trailer lights.  I am looking at a small solar charger for car batteries I can install on the trailer, so it can be completely green and self charging!

  • in reply to michaelkellett

    @Michael Kellett                     http://www.element14.com/community/people/screamingtiger/blog/2015/04/20/a-small-project-idea--wireless-trailer-lighting-control#comment-56732

     

    BTW we have the similar laws in the US.  However, in our case the trailers have to be inspected but what they are looking at is the frame, wheels, bearings etc..

     

    The box you put on top, how you load, or how you light is all done post inspection.    My Harbor Freight trailer came with a DOT certificate and title when I bought it.

     

    There are lighting laws in terms of what lights and colors, but nothing dictating HOW I light them or what types of lights I use, such as LED.

     

     

     


  • in reply to screamingtiger

    The way it works in the UK is that the law says your car, etc must be insured.

    Then the insurance company requires, as  a condition of the insurance, that you tell them if the vehicle has been modified.

     

    You can check insurance company terms and conditions on the web.

     

    In order to fully comply with UK law it is possible that any home built trailer requires a certificate:

     

    Alternatively, specialised trailers built in low numbers can be assessed individually after they have been built. This is done by the Vehicle Operator Services Agency (VOSA), under an Individual Vehicle Approval (IVA) inspection. In this scenario every single trailer produced must be towed to a VOSA test station and inspected. For larger trailers (over 3500kg), certain items (such as Brakes) will have to be tested by an independent party and documentary evidence of compliance obtained, before the trailer can be submitted to VOSA.


    (from Vehicle Certificate Agency document "Advice for companies manufacturing trailers")

     

     

    I'm sure that most home built trailers don't have certificates !

     

    MK

  • This project will be on hold a bit while I will spending my time on my SciFiYourPi project!

    However I may take a sidetrack and do it while I am in the mood.

     

    You know what would be REALLY cool?  A self tracting trailer!  What is that, will the trailer has an electric motor that provides some power for the trailer while being towed.  Why I would want that?   Will then I could pull a trailer with a TINY car.  Like a smart car.

     

    I think as time goes on big vehicles in the US will disappear and this type of concept will be needed.  So the trailer will have to know the velocity and acceleration of the car to provide the right amount of power at the right times.  Probably mostly when moving from a complete stop.

     

    This could be done with an Arduino or Raspberry pi as the control unit.

  • in reply to michaelkellett

    Thanks for the feedback.   I would wonder if what you say about insurance is really true, considering I can go on Ebay and buy some cheap Chinese clone and install that.  I don't know the laws but can you install your own lighting controller and does the insurance tell you that have to use  a "name brand proven commercially available lighting controller?"  If it does then what you say is true, but I would argue something homemade would be no worse than the junk I've been using.  I've been through 3 boxes so far and I have run miles without trailer lights already due to the unreliability.  I even had one box professionally installed!

     

    A couple of notes I should make is that my trailer is not as wide as my jeep.  So that means when someone is behind me, they can still see my brake lights and turn signals.  So there is that safety net.

     

    Another note is my trailer is small and light.  I can pull it up my driveway by hand, fully loaded with airplanes.  So no ABS is needed!

     

    I tend to only drive in daylight as well, but you are correct in that there is a risk element involved.

     

     

    The wireless part of this is more of a "nice to have".  the same concept can be used but with hard wires, except only 1 Arduino may be needed.

    At $75 USD per box, an Aduino micro is much cheaper to replace.

     

    I'd be interested in reading the UK law you refer to.  Can you post a source link?