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.
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