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  • Author Author: screamingtiger
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An Arduino/Raspberry Pi Based Wireless Light Harness

screamingtiger

I am going do this small side project as a way to take a break from my main project.  For a basic introduction please see my original blog post at http://www.element14.com/community/people/screamingtiger/blog/2015/04/20/a-small-project-idea--wireless-trailer-lighting-control

 

If anyone has concerns about my project, please post them in that thread.  I have changed the design slightly after doing  some research and testing.  I am also going to have a control panel in the car with me so I can monitor things as well as manually test the lights.

 

The car has running lights, brake lights, and turn signals all on separate channels.  However the trailer lights only have 2 channels as the running lights also function as turn signals. My initial analysis was incorrect that the running lights also function as brake lights.

 

First a tentative parts list and then I will explain.

2X Arduino mini pros 16mhz boot loader

1X Raspberry Pi model B

1X 2.5" TFT touchscreen LCD

1X 4 channel mechanical relay

6X AMS1117 SO-223 5V regulators

3X NRF24L01+ wireless transceivers

1X 1.5 watt solar charger

3X enclosures

1X 20,000mAh (20Ah) 12V lead acid battery

1X hobbyking 5V/5A regulator

1X 1000 mAh 2s LIPO

 

Explanation of parts :

There are 3 units involved. We have the unit that reads the car's lights, the unit that controls the trailer lights, and the unit that acts as a control panel.  All 3 are connected via the wireless adapters.

 

2X Arduino mini pros 16mhz boot loader

These will be used for the units that read the lights and control the trailer lights.  I have some of these on hand is why I went with them and the small footprint will allow me to tuck it away nicely.

 

1X Raspberry Pi model B and 1X 2.5" TFT touchscreen LCD

This will function as the main control panel with a simple interface.  The Pi attaches easily to the LCD which is why I chose this route.  Its way overkill but I feel it will be useful for other projects that also need a remote or control panel.  The control panel will allow monitoring as well as manual control of the lights for testing.

 

1X 4 channel mechanical relay

The stock lights on my trailer pull 2A for the brakes lights per side, and 500 mA per side for the running lights.  Originally I was going to use a mosfet but I see no reason with this high of current.  The brake lights will be turned on at the same time so the relay will see 4A.  However the running lights will be on separate channels as they also function as blinkers.  The 4th channel I may use to turn on internal lights in the trailer remotely.

 

6X AMS1117 SO-223 5V regulators

These small regulators will be used to power the Arduinos off of the main 12V sources which come from the vehicle as well as the 12V battery in the trailer.  They are also used to read the  vehicle lights.  My plan is to splice into the lines of each light the same way I did before when installing an off the shelf light controller.  The lights will be routed to the 5v regulators which then step down the voltages to 5V for reading via the GPIO pins on the Arduino.  I will need 4 regulators to read the lights.  1 for the brake lights, 1 for the running lights, and 1 each for each turn signal.

 

3X NRF24L01+ wireless transceivers

These 2.4ghz transceivers are similar to an I2C connection and a serial connection combined.  Each one has an ID and you can broadcast information. I will have a small protocol in place for error correction as well as some minor tamper proofing.  I don't want a rogue 2.4ghz signal to be able to mess with my lights.  I will be using a command set that requires a sequence of bytes in order to validate commands.

 

1X 1.5 watt solar charger

These can be had from Harbor Freight and low cost.  I decided that the trailer might as well be "green" and charge its own battery.  Besides its just another thing for me to forget to do.

 

The rest of the items are self explanatory and used to house the items and power the Pi.

 

I may choose to get some LED based trailer lights, but I am going to stick with the stock trailer lights for now until I have a working project.

  • in reply to screamingtiger

    I think there are several ways. One of these - the most easy I suppose - is to pull with a resistor the Vcc from the pin and read its status. If the MCU - I suppose it has - has a VRef for some A/D converter, take a look to the data sheet, you should expect a pin to set fixed (up or down, depends on the MCU logic) to set the VRef as the power Vcc by default. Then when you read this value you are sure that the MCU is working. Maybe a solution ?

  • When reading higher voltages with a MCU, what is the standard way to do that?  I assumed a regulator would be needed.   What do you do if you need to know if a device turned on, in which the MCU did not turn on itself?

  • in reply to balearicdynamics

    I will test it some today, but I can use my multi meter to read 5V from the regulator, I would assume the current draw is also low there.

    If its an issue I will place a 1200 OHM resister fro the output to ground so when it kicks on it will pull 10mA minimum.

     

    The data sheet also says something about using a capacitor on the output, I haven't planned on using that.

  • in reply to balearicdynamics

    thinking thinking ... An alternative - also easier in terms of circuitry, maybe to set a sort of default min loader of 10mA to avoid the fall of load on the regulator ...

  • in reply to screamingtiger

    I took a look to the datasheet to be sure as I have never had to use this regulator. It is a low power low current regulator so I think there is not a minimum current load. The are low max values as the expected operating conditions are (almost large) between 10 and 1000 mA. As far as what I se in the test curves, if I have to use it I suppose that the reliability range should not to be lower than 10 mA. In the technical characteristics it mentioned only 1.5V as the lower min dropout voltage. Take a look to the table below: there is not minimum. but the min load (note 2, fourth colum) mentione 10 mA at the lower dropout voltage. Frankly I suppose that if your load level goes down 10 mA some problem may arise.

    image

    To manage 3.3, instead of regulating a 5V did you though to a fast-response buffer IC? I think that this problems does not exists, but you need two separate power lines.

     

    Enrico