High-power modular lighting systemFollow article
High-power modular lighting system
We set out to design a light that could be mounted and left to illuminate a very wide area quickly and conveniently when needed. The unit features three Cree LEDs to perform this task, with a total output brightness of 8000 lumens.
Some applications of the light are:
- A work light
This unit could be mounted to the inside of the bonnet of a car’s engine bay for inspection and repair by a mechanic when it is dark
This light features output brightness control so the light can be used on low power mode for a very long time.
This is the main reason we designed the light - for illuminating a bike track at night!
Multiple units can be used to illuminate a large area, allowing for the use of sporting facilities in short evenings.
The design process
We have taken the project through the entire PCB and case design process.
- The design need
The process starts with brainstorming what the design needs to accomplish. This step is very important for ensuring the project stays on track and doesn’t aim to accomplish too many things. It can just be as simple as stating that we need to be able to charge the unit up, and have it give out a determined amount of light when it is turned on.
- The schematic
Although you really should spend time further outlining the design, we started work on the schematic. This first started with a brainstorm of what sections we would divide the design into. We narrowed this down to a high-level microcontroller, its low voltage power supply, a 18650 balance charger and a boost converter to drive the LEDs.
We started with the low voltage power supply and microcontroller. For simplicity, we used a linear regulator (L5150-BNTR) with a wide input voltage range and an Arduino Atmega 238p. This configuration allows for the user to reconfigure the code to their desired application if necessary.
The next section was a 18650 charge controller. This is an area to pay particular attention to considering the safety implications of an improper design. This is why we settled on using the AD7280A lithium-ion charge controller from Analog Devices. It supports 6 cell packs and can talk to the atmega 328p with a serial interface for implementing complicated battery longevity code. It also supports an alert function that can warn the high-level controller if any of the cells exceed their operating range. This is a critical safety aspect that should not be overlooked in lithium battery system design.
The lithium pack inside the unit is the most modern, energy-dense way to supply a high current load. Its nominal series voltage of 22V is however not high enough to drive the 36V LEDs. This is why the third part of the board must incorporate a boost converter. This style of switching converter is used to efficiently step up the voltage to drive the load. For this design we used the NCV8870 for its external switching feature, allowing high current capability. As a bonus, it offers very good voltage regulation of its output, which it can adjust many times per second.
- The PCB
After designing a workable schematic, we laid out the components and sent the board for manufacture. For this step, you have to prepare a Gerber file, and send it to a manufacturer. It is important to get this step right or your board might not work! The layout stage took two revisions to route all the traces successfully, and the second revision incorporated important design changes.
The board incorporates tabs for soldering wires for the DC jack, battery pack wires and placeholders for the high power LEDs (shown as red through-hole LEDs in this CAD model.)
- The CAD model
An early prototype
Whilst we were doing all of this, my project partner had been working on a case design to accommodate the 18650 pack, the board and its peripherals, and the LEDs. This stage took several versions to get to a point where we could start to create physical working prototypes.
We have designed a very simple 3D model for a case to house all of the components in one sturdy unit. As a prototype, the case will be printed with PETG in two parts; the 18650 battery sleeve, and the main head unit to house the PCB, LEDs, buttons etc.
In production, the case will be moulded with ABS. This will ensure our lighting system is ready to withstand the elements as well as being more resistant to impacts. This however does not come before more revisions to the case design, incorporating mounting options, an ergonomic rubber grip and the finalised details of peripherals of the PCB.
Pictured below is the board inside the enclosure, and the model of the lens.
From all of this modelling and designing, we could make our first physical unit - no electronics are installed yet.
After putting together the board and the rest of the electronics, we put three units up and tested them at the bike track, all on 1/3 power for extended battery life.