Welcome to the fifth guide in the reef-pi series.

In this guide, we'll use reef-pi to automate a reef aquarium lighting. This guide assumes you have read through the first guide in this series, if not please go through it here.

Lighting is one of the most critical aspects of reef keeping. Corals feed on light. Although corals are animals (thus they cannot do photosynthesis), they have zooxanthellae (a type of algae) in their tissue that forms a symbiotic relationship with them. The algae provide nutrition to the host coral via photosynthesis, while the corals provide the entire habitat for the algae. Tropical corals can survive solely on photosynthesis, though they can also do filter feeding from the water column.

Light controllers in reef keeping are used to mimic natural reef environment. We'll be using reef-pi to automate the dawn to dusk daylight cycle.  Light controllers are also used during the introduction of new corals in the aquarium. Corals are very sensitive to changes in general, and when new coral is introduced in reef aquariums, it is helpful to set up proper light acclimation where light intensity is slowly ramped up to target levels, to reduce the new coral's stress and increase the chance of survival and reduce accidental bleaching.

Sometimes, moonlight or UV lights are used to simulate the lunar cycle. Coral spawning (sexual reproduction of corals by releasing spores) is closely linked with the lunar cycle. Corals contain fluorescent pigments which glow under UV lights. Often times, reef keepers will use UV lights for their viewing pleasure, outside the daylight cycle time.

In the reef aquarium, lighting requires a light source of a specific wavelength (around 460 nm) and intensity (50-200 PAR). Typically reef aquariums require 3-5 watts of light per gallon. There are a number of popular LED lights available for reef aquariums. It is also possible to build a light from scratch using appropriately chosen diodes (generally Cree or Luxeon). In this guide, we'll build a controller for one of the popular LED lights, Kessil, as the main light and an actinic LED strip for moonlight. Although the example circuits are for these specific lights, they should be fairly useful for a host of other commercially available light controls.

Due to the various requirements of light controls and diverse nature of LED lights, reef-pi's light control features are extensive compared to other reef-pi modules. To explore reef-pi light control features, we'll build a dedicated light controller as part of this guide. This controller will automate three Kessil lights (A80, A160, A360) as the main light source for the reef aquariums and a single moonlight strip from TrueLumen, which is mostly used for viewing pleasure, during night time when the main light (kessil) is off. This build is very much customized for my tanks, as shown below, but the technique should be fairly applicable to most other reef tank setups.

For one part of the build, we'll extend our previous reef-pi build to control Kessil lights (A360, A80 or A160),  Kessil allows controlling the spectrum and intensity of the light using 10V pulse width modulation (PWM). We'll use Raspberry Pi's hardware timers as a 3.3V PWM source which will be then converted to a 10v PWM using an NPN transistor. We'll use a couple of LM2596 modules to generate 5V (for Raspberry Pi) and 10V (for NPN transistor source) power source from a single 12V power source.

For the other build, we'll aim to control multiple Kessil lights as well as a moonlight from coralife. We'll need 7 (3x2 +1) PWM channels for this build. We'll use a new Pi Zero along with Adafruit PCA9685 breakout board (since the Raspberry Pi has only two hardware based PWM channels, while PCA9685 has 16 PWM channels)

This parts list does not include the actual lights (Kessil or Coralife). 

A light in reef-pi is composed of one or more channels. Each channel is controlled by a jack, a type of connector (similar to outlets or inlets) that represent a DC current source with PWM capability. The lighting circuit in reef-pi determines how many jacks are available and their supported voltage/current range. For our light controller, we are aiming for 3 Kessil light controls and a blue actinic led strip for moonlight. Each of the kessil light control requires two 10V PWM control signals and the blue actinic led strip will require one more, which makes our total number of required jacks at 7.

We'll be using Adafruit PCA9685 breakout board which offers 16 channels, more than enough for our use. For each channel, we'll use a basic circuit where the 5V PWM signal will be generated by the PCA9685 IC and then a transistor will be used to convert that PWM signal to an appropriate voltage and current for the specific light.  Kessil lights have dedicated 10V PWM control inputs which are different from the actual power source, which makes the control signal current requirement fairly low (under 20ma). We'll use a common NPN transistor 2N2222A for this. There will be six total transistors  to support all 3 Kessil lights, each with two channels.  For the actinic LED strip we'll use a TrueLumen actinic LED strip and dim it by controlling its power source directly using a power MOSFET.

Here is an overall schematic of the wiring. We'll use a single 12V 2A power supply to power the entire project. Two LM2596 modules will be used to generate 5V (for Raspberry Pi & PCA9685 breakout board) and 10V (for Kessil circuit) power source from a single 12V rail. The 12V rail will be used to feed the actinic strip as well, connected via a 2.1mm barrel jack connector.

Notice there are two perma proto boards used in this build. A half size perma proto board has the Kessil control circuit, which involves one NPN transistor for each channel, the PWM output from PCA9685 IC is connected to the transistor base (green wire) with a 10K resistor in series.  While the 10V rails are connected to the collector pin (blue wire) of the transistor with a 1K resistor in series. The emitter pin of the transistor is connected to GND.

The power MOSFET based control circuit for the 12V actinic LED strip is mounted on a small Mint Tin size perma proto board. A common N channel logic level power MOSFET is used, with the PCA9685 PWM output connected to the Gate pin (green wire), the Source pin connected to the -Ve end of the LED strip (blue wire) and the Drain pin connected to GND.

Start with preparing all the connectors. We'll need two barrel jack connectors, one for the incoming 12V 2A power source and another for powering the actinic LED strip.  We'll also use an SPDT switch for convenient power up or power down of the controller.

Always tin the connectors and the jumper wires before soldering. 

Next, build the Kessil control circuit on the half size Perma Proto Board. I have used color-coded male header pins and jumper wires to make it easy to understand the circuit. The green header pins represent inbound 5V PWM signal from PCA9685. They are in pairs, since each Kessil light has two controllable channels. The blue header pins are for 10V PWM that will be generated by the transistor. Each of the light control signal involve two 10V PWM channels and a GND.

Add NPN transistors and resistors.

Then solder the jumper wires and male header pins for power rails. I use 22AWG solid core wires for this. The upper power rail is used for 5V and the lower power rail is used for 10V.

Next, build the actinic LED strip control circuit on the Mint Tin size Perma Proto Board. This board will also provide a 12V that is used to power the LM2596 modules.

The actinic LED strip comes with bare wires. Connect with a 2.1 mm male barrel connector.

Start with drilling holes for all the connectors. I prefer to mount connectors at the bottom of the panel. Note the barrel jack connector holes (the first two on the left) are little bit bigger than the holes for 3.5mm audio jacks (right three holes).

Drill a hole for the SPDT switch that will be mounted on the side panel and proceed to mount the electronics. I start with the PCA9685 breakout board. All the breakout boards, Pi and Perma Proto boards are mounted using nylon standoffs. I tend to place them inside the enclosure first, then mark down their PCB holes and then drill the enclosure on those spots to screw fit the standoffs.

The LM2596, Pi and the Perma Proto boards are mounted. SPDT switch, power source and LM2596 input power pins are all connected.

The rest of the pins are then connected with female-female jumper wires. I sometimes resize them by manually stripping them off and connecting dupont female connectors of the appropriate length.  I also use color-coded heat-shrink tubes just to group similar connections. In this build, the PCA9685 PWM outputs are connected with jumper wires in the yellow heat-shrink tube and the 10V PWM outputs are grouped in the green heat-shrink tube. The blue heat shrink tube groups the i2c jumper wires (SDA, SCL) that connects Raspberry Pi with the PCA9685 breakout board. Use the adafruit guide on PCA9685 to get started with this versatile chip if you are not familiar with it.

That's it, our reef-pi light controller is built. Here is a side view of the controller from showing the SPDT switch

And this is the bottom side view, showing all the connectors. Left most is 12V 2A power input, then 12V PWM power output for actinic LED strip and then three 3.5mm audio jack connectors for Kessil lights, each having two 10V PWM control signals.

Next, we'll power up this build and learn how to use reef-pi software features to automate the lights

Before powering up the entire build (the Raspberry Pi in particular), make sure the LM2596 modules are correctly tuned to generate exactly 5 and 10V output. Crosscheck with a multimeter the power rails on half size Perma Proto board (5V above, 10V down) as well as the mint tin size Perma Proto board (12V) are as expected.

Once everything is as expected, connect the Raspberry Pi power pin (Pin 2) at the end and power up reef-pi.

Once reef-pi is running, go to the UI and declare jacks under the Connectors section in Configuration tab to represent all four connectors. There are three Kessil connectors, J1 to J3, connected to pin 0, 1 and 2,3 and 4,5 respectively. Make sure to choose pca9685 as the driver. I am using the PCA9685 pin 12 to control the power MOSFET.

Next, create lights and associate the relevant jacks with the lights.

Next, create four lights to test all the connectors. I am declaring three of my Kessil lights, for example.

Once created each light can be controlled independently using profiles.

The fixed profile allows running lights in a constant brightness or color. This is generally useful for creating on-demand moonlights or during photo shoots of the tank. 

The diurnal profile allows users to simulate daylight cycle by an exponential ramp up and ramp down with most of the time operating at maximum PWM value. The diurnal profile cannot be visualized in the reef-pi dashboard itself, but if you have adafruit.io integration enabled, then you can observe the diurnal profile generated PWM values in your adafruit.io dashboard. Here is an example from my build:

The auto profile allows users to set a specific light intensity throughout the day at two hours interval. reef-pi linearly increments/decrements the PWM values in between the two-hour intervals. This is an effective way to simulate the daylight cycle with finer control over how steep the PWM value ramp up/down will be.

We can configure the reef-pi dashboard to show the light profile in "auto", to visualize how individual channels will be ramped up or down throughout the day.

This build guide covers Kessil and actinic led strip controller, but the basic circuitry should work for a variety of led light types. reef-pi community members have used raw power MOSFETs to a Meanwell LDD driver based control circuit for other proprietary/branded lights or cheaper (and often times not UL listed) black boxes or completely DIY lights made with Cree or Luxeon LEDs (3W).

This guide uses an Adafruit PCA9685 board, which gives up to 16 PWM channels. If you need only two PWM channels (e.g. only one Kessil light controller) then you can just use the Raspberry Pi. reef-pi can use Raspberry Pi's hardware timers (GPIO pin 18 & 19) natively for PWM. Just remember Pi based PWM pins are limited to two and in reef-pi UI they are denoted as pin 0 and 1 for GPIO pin 18 and 19.

Thank you for reading through the light controller guide, we'll look into the pH monitoring module in reef-pi in our next guide.