Arduino controlled plant light (and general indoor light) - Page 1
Forum section: electronics / projects

author: Kester
author_rank: Newbie
timestamp: May 06, 2020, 07:45:02 pm
content: This is my first time working with high power LEDs and also my first time designing and ordering a custom PCB. Thanks in advance for the input!The plan is to build an Arduino shield that controls 4x LDD-L series Mean Well constant current drivers with the PWM output of the Arduino, and connect this LED driver board to a custom metal core PCB with surface mount LEDs. Later I will expand to multiple boards. I chose to build a custom PCB for mounting the LEDs because it let me achieve a more streamlined look (most high power DIY lighting is for plants but this project is for indoor plants and should also function as general indoor lighting). Some details belowPowerA 24V AC/DC converter to power both Arduino and LEDs (via Mean Well drivers)Arduino ShieldHolds 4 Mean Well DC/DC drivers each wired to Arduino PWM pins 5, 6, 9 and 10 (these are the pins for timer/counter modules 0 and 1). I will only use 3 but having space for one more adds flexibility at no cost.For a more compact design, the shield will also provide 5V power to the Arduino. This requires a DC/DC converter, and for flexibility the PCB can accept any SIP-3 DC/DC converterLED BoardDesigned to be attached to a heatsink (VHS-95) at the corners with M3 nylon screws.Other holes are for mounting a lens for the LEDs (lens will be glued to the PCB but aligned using the holes).Holds 4 3535 SMT LEDs (like CREE XP-E and XP-E2). Two are in series (for red LEDs). I put these diagonally for a more even light pattern.The heatsink + LED unit is intended to be hung from a shelf (with sufficient clearance for convection) and the wires connecting to the Arduino shield will also run along the bottom side of the shelf.The PCB has a tab that extends beyond the heatsink, which holds a reverse though-board SMT pin header (TE Connectivity part no. 2106091-5). That is, the pin header is surface mounted on the bottom (LED) side but extends backwards through a hole in the board. This means that all components are soldered to the bottom face of the board but the wires plug into the top side. This gives a more streamlined look since the wires point upwards from the board.A few questionsIs it worth adding external pull-down resistors on the PWM output? This might guard against failure of the Arduino, defaulting to no power instead of full power in case PWM signal is lost. The Arduino can be programmed to have internal pulldown resistors which would guard against some kinds of software failure.The LED board is quite large and only attached to the heatsink at the corners. Will this create problems with the thermal interface between the board and the heatsink? I could add a screw in the middle but that would require drilling my own hole in the heatsink, while the other holes are pre-drilled.Any comments on the shape of the tab on the LED board?The next phase after this is built is to add a real time clock module to allow for automatically changing the light pattern based on time of day, and also and IR LED receiver module to allow for controlling the lights with TV remote. Typical usage would be having two modes (both of which follow a time-based schedule) plant-mode and indoor-lighting mode. Plant-mode is for when I'm not home. The TV remote would alternate between the modes (and other manual control). Any suggestions or comments here? I'm especially interested in how to design the Arduino shield now to accommodate these so that I don't have to order more PCBs later.