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M.O.S.A.I.C. LS

Modular Open Source Adjustable Intelligent Control Lighting System

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The goal of this project is to create a robust, modular and scalable system for lighting whose applications include (but are not limited to) grow lights, work lights, ambient lighting for living spaces as well as photography and video. The ultimate test for MOSAIC LS would be to implement it in space applications where artificial lighting is required from growing food to crew psychology.

Robustness, modularity and scalability are achieved by keeping the design as simple as possible. The physical shape of the light is an equilateral triangle which can be arranged into many pseudo-shapes (as per application). Its cell like nature allows it to be used individually or in large arrays.

Control is over RS485/UART using MODBUS protocol. It can be powered with nominal voltages between 12VDC - 24VDC allowing for industrial and automotive applications.

This project initially stemmed from my unconditional love of Okra before it became what is now MOSAIC LS. I wanted to see if I could grow Okra in the cold, dry climate of Alberta, Canada but It proved to be more difficult than originally thought.

Before we dive into the 'deets, lets start off with some common nomenclature which will be used throughout. The assemblies are arranged in the same manner as photo-voltaic applications:

  • "Cell" - PCB containing the emitters and uC
  • "Module" - collection of interconnected cells in the shape required by application
  • "Panel" - collection of interconnected modules
  • "System" - collection of interconnected panels

Due to safety, legal and long term reliability concerns, the UV emitters were removed from the grow light variants and a 4th variant was added (GUVL - General Purpose UV Light). This new UV variant includes design elements that will protect against UV degradation as well as additional safety interlocks. This should make using the GUVL variant safer with increased reliability.

The 4 proposed variants are:

  • AHLS - Adjustable Hue Lighting System:
    • ~625nm red emitter
    • ~525nm green emitter
    • ~470nm blue emitter
    • 5000K - 5700K white emitter
  • GTGL - General Purpose Terrestrial Grow Light
    • ~740nm far red emitter
    • ~660nm red emitter
    • ~525 green emitter
    • ~470nm blue emitter
    • ~450nm royal blue emitter
    • ~5000K - 5700K white emitter
  • GAGL - General Purpose Aquatic Grow Light
    • ~660nm red emitter
    • ~525nm green emitter
    • ~470nm blue emitter
    • ~450nm royal blue emitter
    • ~425nm violet emitter
    • ~5700K while emitter
  • GUVL - General Purpose UV Light
    • ~385nm UVA emitter
    • ~310nm UVB emitter
    • ~280nm UVC emitter

For this project, we will be looking at the GTGL variant as it encompasses all aspects of design that are common to the other variants.

The cell is composed of a triangular PCB which contains:

  • a uC (microcontroller)
  • various emitters as per product groups
  • 3x connectors
    • one connector on each side
    • each connector with symmetric pin layout to enable connection to other cells without worry of orientation
Figure 1
Figure 1: Cell dimensions and M3 hole provisions

It's physical dimensions are based on an equilateral triangle (Figure 1, outlined in gray) whose sides measure 62.5 mm. The corners of the triangle are equipped with holes to accommodate an M3 socket head cap screw. This screw is connected to ground ("GND") of the cell. Adjacent to the ground screw are identically sized holes but half-way to the edge and connected to main power ("+V") which in this case is 12V DC nominal. This simplifies carrier/housing design and power supply routing. Wires can be soldered on either side of the PCB or a carrier board with spring clips can be designed where the cell just clicks into place.

Figure 2
Figure 2: IO connector pad pitch (50mil / 1.27mm)

The connector design and layout are chosen to allow maximum application flexibility. It is a hybrid through hole/surface mount pad with symmetrical pinout. Designed to allow 50mil pitch headers to be soldered directly to the cell via the available through hole/SMT pads. In addition, flat cables with similar pitch can also be soldered directly. See Figure 2 above for pad pitch screen cap.

Figure 3
Figure 3: IO connector pinout.

The connector pinout (Figure 3) is laid out to allow adjacent cells to be "butted" up and directly soldered without the limitation of orientation of the cells. See Figure 4 below for an example of "butted" connection.

Figure 4
Figure 4: IO connection "butt" joint.

Cells communicate over RS485 using MODBUS as the protocol of choice. This allows for communication with each cell regardless of how deeply embedded they are in their application and can be dropped into existing MODBUS networks. For local communication (single cell interface, cell to cell etc.), the RS485 line driver can be bypassed and 3.3V UART used...

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cell_625.step

Step file of the PCB with uC, LEDs and constant current drivers.

step - 3.98 MB - 03/16/2018 at 03:46

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  • 1 × LPC824 Curently, the LPC824 is being used as the uC for development and evaluation. Later I would like to move to an STM32F0 which has USB for ease of use by the end user.
  • 6 × XP-E2 LEDs
  • 6 × AL8860 LED constant current driver (buck converter)

  • LOG 20180414: Revised PCB and Stencils!

    slisgrinder6 days ago 0 comments

    So I wasn't expecting this but I ended up getting both the revised PCB AND the SS solder paste stencil at the same time in the mail!

    I am always interested in seeing how everyone packages their products and I have to say even OSH Stencils did a fabulous job.

    I especially like the caution sticker on the top! The stencil came out real nice and it was definitely worth it. I can't even complain because I don't know of anyone that can beat their price to be honest.

    The PCBs of course turned out great and visually there seem to be no issues. I am always surprised at the quality of the silkscreen and how its so crisp looking.

    Overall I am quite happy and can't wait to get this version built - with heatsinks this time!

  • BACKLOG 20180322: First Hot Test

    slisgrinder04/06/2018 at 03:05 0 comments

    Reruns received...

    I received the reruns from OSH Park and they look beautiful!

    Figure 1: Top side of rerun

    Top side looks great, just like the previous run.

    Figure 2: Bottom side of rerun

    And, the back side looks as its supposed too!

    Figure 3: Bottom side IO interface

    A quick continuity test reveals that all is well and that all the internal layers are intact.

    Hot test...

    After a quick order on DigiKey, I received the parts and began the reflow soldering of the LEDs and their respective buck converters. The LEDs were the most difficult part because I didn't want to damage the LEDs by using the hot air pencil above them.

    Figure 4: Board populated with 2700K LEDs on left and 5700K LEDs on the right

    I also ended up just soldering wires to the micro controller pads that are supposed to be the PWM outputs to the buck converter. This way I can test it using another microcontroller board or in my case a function generator.

    Figure 5: Board all soldered up complete with PWM wires

    In case it wasn't clear about how to power the board, Figure 6 shows how the screw and wire combination power pads are used.

    Figure 6: Power wires to board

    Hot problems...

    Unfortunately I wasn't able to pictures of the circuit in operation because I ran into some problems. First off, holy crap are these bright! At first I was only able to the the 2700K LEDs working but after a quick reflow to ensure all the LEDs had settled, the 5700K turned on. As bright as they are, they also get hot very quickly, thus I wasn't able to run them long enough to take a picture. This heat was somewhat manageable at a PWM duty cycle of 20% @ 100Hz but even then I could only run them for no more than 10 seconds. I suppose the next order of business is to look at heat sinking and some temperature measurements.

    Some quick measurements confirmed that the LEDs are consuming just under 6W per pair. Each cell has 6 pairs of LEDs so that means I am going to have enough heat to desolder the LEDs. Fun...

    Then I did the stupid thing... I increased the supply voltage up to 24V and then all the LEDs turned off. I went over the reverse bias voltage causing them to short for a fraction of a second and then fail in the open. I have already made the necessary changes to the BOM so that all components can withstand the rated 40V input.


    As an aside, while I was troubleshooting what happened to the diodes, I came across a PCB layout error. The footprint of the LDO linear regulator used for the microcontroller power was incorrect. I switched a couple of pins around probably when I was looking at some other part. In any case, the issue has been resolved, new gerbers were produced with the corrections recommended by OSH Park and they should be on their way to me soon. I also ordered a stencil from OSH Stencil so that should be exciting...

  • BACKLOG 20180202: PCB Issues & Fixes

    slisgrinder04/05/2018 at 02:09 0 comments

    I Did This To Myself...

    So I placed an order with OSH Park for the PCBs on January 13th and I wasn't expecting them to be here so soon!

    1st Cell Prototype
    Figure 1: 1st cell prototype
    1st Cell Prototype Backside
    Figure 2: 1st cell prototype backside

    The silkscreen turned out fabulous; the soldermask and hole registrations are VERY good. And then I noticed something...

    If you look carefully at the soldermask in Figure 2, notice the lack of copper pads where the ground pads and screw pads are. A quick continuity check further confused me as all the IO connections were shorted together along with the power pads on the side and the corner ground pads.

    Looking further at Figure 2, you can see that the vias seem raised and bumpy. The same can be said about the power pads and IO connectors. Compared to Figure 1, all seems well on the top side of the board.

    Cell Edge Inspection Top
    Figure 3: cell edge inspection top
    Cell Edge Inspection Bottom
    Figure 4: cell edge inspection bottom

    A quick look under the inspection scope shows a potential problem in the IO connector. Figure 3 shows the top side (LED side) on the left and in focus. Figure 4 shows the bottom side on the right and in focus. The IO pads seem to be connected on the bottom layer and on the top they are isolated as they should be. Also of note are the internal layers visible in both inspection pictures.

    Cell Prototype Missing Plane
    Figure 5: cell prototype missing plane

    It seems that the ground plane on the bottom later is entirely missing (as outlined in Figure 5). However, the IO connector pads are all shorted together. Weird...

    The Fix...

    I informed OSH Park about the issue and their response was quick and quite unexpectedly detailed. They were so awesome in fact that they dug deep to figure out the problem and over the weekend at that! It turns out it was partly my fault although I didn't know it at the time.

    Cell Ground Plane Over Extended
    Figure 6: cell ground plane over extended

    The internal planes were initially setup as an equilateral triangle but my board outline cut through them. This meant that there were parts of the planes outside the board as shown in Figure 6 (top portion of plane visible above and past the center "GND" screw pad). When the gerbers were processed by OSH Park, the over extending parts of the plane were removed. However because they are part of the same plane entities, the entire plane was removed and funkiness ensued.

    The folks at OSH Park were very thorough in their investigation and offered a very concise explanation in a timely manner. They were nice enough to rerun the boards for me at no cost and even offered expedited shipping!

    Thank you OSH Park!

    OSH Park, thank you very much for the help. I learned something new and I hope other companies follow your lead...

  • PCB Elements and Features

    slisgrinder03/24/2018 at 23:31 0 comments

    PCB Layout...

    There was some back and forth about how many layers the PCB had to be. For keeping things cheap, the obvious choice would have been to use a 2 layer board. However, there needs to be a balance between being cheap and being simple. Sometimes to be simple you have to be a bit "anti-simple". The decision was then made to use a 4 layer board as it has significant benefits:

    • Meets size constraint for part placement and routing
    • Ample room for thermal management without traces in the way
    • Routing got VERY easy
    • Gives way for large planes
      • Very important in the overall design
      • Does not require the need for bus bars or external power distribution. The boards themselves can carry the required current.
    Gerber Top Render
    Figure 1: Gerber top render
    Gerber Bottom Render
    Figure 2: Gerber bottom render

    The PCB stack up is as follows:

    Gerber Top Layer Render
    Figure 3: Gerber top layer render
    Top Layer
    - Contains all the electronic components
    - Poured as "+V" to provide a large current path for adjacent cells
    Gerber Signal Layer 2 Render
    Figure 4: Gerber signal layer 2 render
    Signal Layer 2
    - Contains 3.3V distribution and PWM control traces.
    - Poured as "+V" to complement the Top Layer plane.
    Gerber Signal Layer 3 Render
    Figure 5: Gerber signal layer 3 render
    Signal Layer 3
    - Contains all RS485 and UART lines interconnecting the 3x edge connectors.
    - Poured as "GND" to provide a large current return path as well as thermal distribution plane for the LEDs.
    Gerber Bottom Layer Render
    Figure 6: Gerber bottom layer render
    Bottom Layer
    - Poured as "GND" to complement the ground plane in the previous layer as well as a uniform thermal plane for heat sinking.

    PCB Features...

    The PCB has pads attached to the "+V" and "GND" plated M3 screw holes to allow up to 12 AWG wire to be directly soldered. With the help of the large power planes in the board, there is no need to have external power distribution between cells. The pads are identical on the bottom layer and enable various mounting options such as carrier boards, spring contacts, direct wire to board soldering, etc.

    The I/O connector is symmetrical in design. It can be used in any orientation with other cells and facilitates the use of wires, flat cables, headers, spring contacts or direct "butt" joints with adjacent cells. Power can either be applied with the screw hole pads or the I/O connector. When assembled as an array, it is recommended to use the screw hole pads for the initial power entry into the array and the I/O connectors within the array.

    Power Pads
    Figure 7: Power pads

  • Cell Size & Shape Justification

    slisgrinder03/24/2018 at 01:38 0 comments

    So the cell was decided to be an equilateral triangle whose sides measure 62.5 mm... But why?

    One of the goals for the MOSAIC LS project is scalability. How do you shape a component that can conform to any application thrown at it, scalable? Why, triangles of course!


    ... Triangles are forever...

    A triangle is the most basic enclosed shape that can be formed with the least number of sides, 3 in this case. Its used in graphics to reduce the number of vertices in a mesh while retaining the most detail as well as in structural engineering. With triangles you can assemble them into whatever pseudo shape you want. They can approximate circles, rectangles and its not limited to just 2D shapes. They can approximate spheres , rings, domes, boxes, cylinders, etc.

    So that addresses what shape to make the "cell" into - an equilateral triangle which keeps things as symmetrical as possible. But what about its size, how big should it be? Too small and complexity becomes an issue as more are required. Too big and it might hinder certain application constraints such as portability or tight spaces.

    ... Who said size doesn't matter?...

    To address the question about how big to make the triangular cell, first we have to consider what applications the MOSAIC LS cell could be used in. One of the key applications that had a heavy weight on design considerations was solar. Many projects out there use solar as their method of energy collection, storage and usage.

    125mm x 125mm solar cell
    Figure 1: 125mm x 125mm solar cell, one of the most common sizes.

    After a few deep dives on the 'webz, some querying around work and physically measuring dimensions of cells in solar panel assemblies, a conclusion was reached. The most common size of solar cells (monocrystalline or polycrystalline) was a pseudo-square cut from a 160mm diameter ingot of silicon. It measures 125mm x 125mm with corners of 160mm diameter. See Figure 1 above.

    If a cell were to be designed with the sides of the triangle measuring 125mm, then one would be left with 1/2 the solar cell uncovered. However if a circle with a diameter of 125mm is considered, it will cover approximately 75% of the cell. The best approximation of a circle using the least amount of triangles is a hexagon. That means there are 6 equilateral triangles whose sides measure 62.5mm in length. See Figure 2 below.

    Hexagon made from 62.5mm equilateral triangle
    Figure 2: Hexagon made from 62.5mm equilateral triangle

    Lets see that hexagon with the actual cell PCB outline (Figure 3)

    PCB cell hexagon solar cell
    Figure 3: PCB cell hexagon solar cell

    A near perfect fit with just enough room to add some switching circuitry to boost the cell voltage and to hide a beefy battery behind the hexagon assembly.

    ... The Goldilocks Principle...

    When you consider that particular dimension, 62.5mm, that's 2.461 inches which is just enough to design an enclosure whose outside dimensions don't exceed 2.5". Its small enough for portable applications as a single unit or in pairs/triplets. It's just big enough to be used in large numbers without adding too much complexity and does not exceed the available MODBUS addresses (254) to comprise a 1m x 1m array. Among many other things, it all works out!

    Not too big... Not too small... Just right.


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slisgrinder wrote 15 hours ago point

Thank you everyone for the follows and likes. It really means a lot to me and is very motivating to continue development on this project.

Cheers!

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