I thought to myself, what a great opportunity for me to put together a DIY electronics project that would also be green. I wanted a quick and inexpensive solution so I decided to go with the Arduino as the MCU and build everything from scratch.
This document will document my project from beginning to end.
I had picked up a battery powered LED light that would be great for this project.
I have a bunch of ATMega chips lying around as well as a few Arduino clone boards, so I was well on to my way of building this project with material and parts that are in my parts bins in my shop.
I started to think about what kind of design I wanted and decided to go simple, lean and mean.
I have done some work with latching relays in the past and really like the idea of using the MCU to latch the relay on and off without having to keep constant power on the ATMega ports all of the time.
The chicken coop is located in an area where there is no easy access to AC power and I wanted a battery solution that I could, at a later date, add solar panel access for charging.
First off I had to determine the volts and amp requirements of the LED light.
I took the LED light apart and soldered some wires to the existing switch circuit so I could trigger the light with the relay.
The LED light consumed 6 volts at around 500 milliamps.
D-cell batteries originally powered the LED light. I did not want two different battery sources and I did not want to change batteries all of the time. So I decided on a single battery source to power the MCU and LED light.
Below is image of LED light mounted in Chicken coop, two wires for switch and two wires for power:
Step 1: Breadboard
I also do not like to power external devices directly from the microcontroller ports so I decided to use some NPN transistors as part of the relay circuit.
To provide an accurate time source for the relay timer I decided to use a DS1307 RTC, Real Time Clock chip. LadyAda has a really good write up on using this chip and has created her own code branch of JeeLab’s RTCLib library.
Here are the links to the web sites:
The breadboard shows a SparkFun DS1307 RTC, I have several of these that I use for testing purposes.
But the production version of the Light Relay board uses the same RTC board that LadyAda documents in her writeup.
The Arduino clone pictured is the Diavolino from Evil Mad Science Labs. Nice board and very inexpensive. I use this board as one of my prototype boards.
Since I needed two different voltages for this configuration, 5 volts for the microcontroller and 6 volts for the LED light, I decided to use two linear power regulators. For low cost I decided to use 7805 and 7806 regulators to drive the microcontroller and the LED light.
Since I wanted to keep the price low, I decided to build the production version of the circuit board on solder based breadboards.
After building this board, I learned a lot of lessons, In the future, I more than likely take the time to build my own custom PCB boards.
Building the solder breadboard was very time consuming and tedious.
Step 2: Production Breadboard
Notice the terminal blocks on the breadboard.
The left terminal block is connected to the two switch wires of the LED Light. The output from the relay is connected to this terminal block.
The terminal block on the right is the voltage input for the microcontroller and relay circuit.
The 90 degree header pins are used to upload the Arduino program to the ATMega 328P. Notice the red wire just below the right terminal block.
This wire was originally set up to connect to the USB power lead of the FTDI USB-TTL cable.
This way I could power the circuit from the USB port when I was debugging the circuit.
Just before installation I removed the lower red wire so I could power the circuit from the right terminal block from the single source battery.
My biggest expense was to purchase a deep cycle 12-volt wet cell battery.
The amp hour rating on this battery was around 110 amp hours.
This way I could power the board and light for several weeks on a single charge.
I decided to re-charge the battery once a week, until I can add the solar panel charging circuit.
Step 3: Mounting
Below is an image of the finished case with the circuit boards mounted:
Notice the top terminal block. This terminal block provides 12 volts from the deep cycle battery and powers the voltage regulators.
The lower left terminal block on the voltage regulator board provides 6 volts to power the LED light.
The right terminal block on the voltage regulator board powers the microcontroller circuit.
I also purchased a plastic battery box and mounted the micro-controller, relay circuit and the battery in this battery box just behind the chicken coop.
Step 4: Coop Mounting
Step 5: Circuit Diagram
Step 6: Adruino Code
I have included two programs that can be used as is or modified for your custom use.
One program, RTC_Relay, this program is based on turning the relay on and off within a 24 hour period when the end time is greater than the start time.
The second program, RTC_Relay_DHMS, Allows a Start Hour and a Start Minute to be set, and a day, hour, minute and second duration to be set.
When the Start Hour and Start Minute time is reached the relay is turned on and stays on for the given day, hour, minute and second duration.
The code is well documented and I have given Creative Commons license to the code, so please feel free to use the code as long as you give me credit in your code.