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UVA

High-power ultraviolet flashlight for curing UV adhesive (https://bit.ly/FldRdy-DB)

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When a humanitarian crisis hits, Local communities are in the need of relief, recovery and reconstruction. To do so, it is necessary to have the tools for these tasks in a faster, better and cheaper way than today's supply chain. NGOs have to be effective in delivering their aid and people should be empowered with the knowledge and the skills to face the crisis by themselves in a resilient way.

UVA offers much more than a UV-A light tool for curing glues in adverse situations. It is a multi tool kit system designed to encourage people to create their own exchangeable instruments relying on a battery pack and a plug and play connection. UVA is based on the ideas of cost-effectiveness, local production, reparability, hardiness and intuition. It is designed with the most common and available components in the market to increase its accessibility. We have the conviction that most of the mechanical parts of the system should be produced locally with 3d printing and recycled material


Table of Contents:


Design Specifications

  • Requirements by Field Ready
  • Introduction to the UV curing process
  • Market research on available UV flashlights

Led Power System

Rechargeable Battery System

  • Choosing the Batteries
  • Designing a battery protection system
  • Integrated Li-ion battery charging circuit
  • Input power-path multiplexing

PCB Design

  • Designing a testable and reparable PCBs
  • Soldering SMD cheaply with sand
  • Writing a troubleshooting and testing manual

Manufacturing

  • Assembling and disassembling instructions

Testing Procedures

  • Testing the LED drivers
  • Testing the voltage regulator
  • Testing the battery protection circuit
  • Testing the battery charger
  • Testing the power-path multiplexer
  • Integration testing the whole system

Licenses

All the hardware components of this project are licensed under a Creative Commons license

Creative Commons License
UVA by Said Alvarado, Miguel Fernandez is licensed under a Creative Commons Attribution 4.0 International License.

All the firmware of he project is licensed under the MIT license.

Copyright © 2020 Said Alvarado and Miguel Fernandez

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

  • High-efficiency LED driver circuit

    Said Alvarado Marin08/30/2020 at 21:16 0 comments

    Having previously decided which, and how many, LEDS we are going to use. It is now time to design a driver to power them. This post goes through the calculations needed to design the circuit, the following post gives some recommendations on designing the PCB.

    Here is the final product.

    26.4W Boost LED driver schematic
    26.4W Boost LED driver schematic

    26.4W Boost LED driver PCB - 3D view
    26.4W Boost LED driver PCB - 3D view

    Choosing the main driver IC

    According to our calculations, to achieve max brightness we need a driver capable of providing 1Amp @ 26.4V (the combined forward voltage of 6 ls). Also, since our power source is a 3S Lipo battery, we need a BOOST driver, as the voltage provided by the battery 11.1v will need to be stepped up to the voltage required by the LEDs. 

    We chose the AL8553 because it has an external MOSFET, It's small, inexpensive, has good integrated over-current and over-voltage protections, supports dimming control through PWM, and comes in a leaded IC package (important for ease of soldering).

    Recommended circuit for the AL8853.
    Taken from the AL8853 Datasheet

    Designing the Circuit

    Designing switching converters is hard. Thankfully, the datasheet has all the instructions and equations required. Now, we only need to calculate the value of the components in the example schematics.

    We are going to number the equations with the same numbers as the datasheet, so you can follow along if you want.

    L1:

    This is the main switching inductor of the circuit. Here's we need to calculate its Inductance and the Maximum Current it will handle. Here are the variables we know:

    • Output Voltage: 26.4V
    • Led Current: 900mA (To run the Leds at a little less than maximum power)
    • Input Voltage: 11.1V (Nominal of a 3s Lipo battery)
    • Efficiency η: 0.85 (Standard efficiency of BOOST drivers)
    • Ripple Current Rate γ:  0.5 (Datasheet, p.10 suggest between 0.3 and 0.5)
    • Switching Frequency f:  120Khz (According to datasheet p.4 table)

    First we calculate the average current through the inductor:

    Then the peak-to-peak variation of that current.

    Now we know the maximum peak current that the inductor will need to withstand at any given point (And we can oversize it by 20% just to be sure):

    Finally, we can calculate the inductance value like so:


    Ok, so we know the inductor needs to be L1 = 43uH @ 3.8 Amps.

    Looking through Mouser, I found this one that I liked SRP1265A-470M (Link to mouser listing) from Bourns it's the exact same inductance value, but 47uH is close enough..

    Inductor L1
    Inductor chosen for L1, picture from the Mouser Listing

    R6:

    This resistor controls how much current goes to the LEDs. And, assuming a LED current of 900mA can be calculated with the following formula:

    This resistor is in the path of the led current, so it's mportant to double check his power dissipation.

    Therefore R6 = 0.222ohm @ 180mW

    or if you prefer  to run the LEDs at 1Amp, R6 = 0.2ohm @ 200mW

    I liked the RCWE1206R220FKEA for the 0.222ohm, and the RCWE1206R200FKEA for 0.2ohm. They are high precision, and are rated for 0.5W of power.

    Curent sense resistor R2
    Resistor chosen for R6, picture from the Mouser Listing

    R3:

    This resistor controls the over-current protection trigger. The datasheet recommends setting this trigger point using 30% more than the maximum current expected by the circuit. Which happens to be the maximum peak current of L1, at the lowest expected Vin: 9v (The lowest safe voltage of a 3s lipo battery).

    Using the equations from L1, we can calculate this peak current.

    Finally, we over-size it by 30% to find the Over-Current Protection Current.

    And now R3 is equal to:

    We can also calculate the power consumed, just as we did with R6. Which means

    R3 = 60m @ 0.54W
    That's a lot of heat for an SMD resistor, So it is important to size it appropriatly. I found the WSLT2010R0600FEB18 to be adequate for the job.

    Resistor chosen for R3, picture from the Mouser Listing

    R4 and R5:

    This resistors are used in a voltage divider that sets the trigger...

    Read more »

  • UVA Joint_V2

    Miguel Fernández08/26/2020 at 16:32 0 comments

    After a lot of tests and fails with UVA joint V1, we have developed a second version that solves the weaknesses of the first attempt. The main fail with the V1 was in the snap-fit cantilever connection in the legs ring (UVA-MJ-LV1_1b). This is the part of the joint that will be attached to the tool.

    UVA-MJ-LV1-3 Fail

    As you can see in the pictures it failed because of the lack of stiffness in the legs. The vertical force practised by the bending piece "1a" in the snaps ring at the moment of snapping also bent the legs in the legs ring. This part wasn't either design or prepare to bend. Because of the way that FDM 3d printed pieces work, the maximum flex and bend resistance is achieved parallel to the layers. In this case, the force applied to the leg was perpendicular to the layers and, after some attempts to connect both rings, the piece failed and break in the joint between the plastic layers.

    In the UVA Joint V2 (UVA-MJ-V2) we increased the area of the legs to achieve the necessary stiffness to prevent bending and also to increase the surface of contact between the layers. With the new solution came some new problems, mainly related to the printing process. The leg parts both snap-fit and locks have to fit in the snap parts with not too much tolerance to guarantee a good joint. So the termination of those has to be very precise and it is necessary to avoid supports to print the legs. As you can see, we left some holes over the legs to guarantee a qualitative termination.

    Furthermore, we already took the next step and designed the electrical connection in the legs ring, and we are really close to finished the battery pack design but it will be discussed in another log. 

  • We bought a 3D Printer

    Miguel Fernández08/26/2020 at 13:07 0 comments

    Thanks to Hackaday and the community vote for awarding us with the bootstrap money. One of our investments in the project was to buy a 3d printer. The reason for this decision was based on the fact that we needed to experiment with the 3d printing process. It was necessary to take full control of all the steps of the 3d printing because we have to improve the design in its final stage but also in the fabrication process.

    With the 3d printer, we can optimize the use of plastic, temperatures, the resistance of materials, and we have the tool to create a detailed manual of how to produce UVA.

    We buy a Creality Ender 3, it's one of the best in relation to price and quality. If we are designing a product to be built in adverse situations, It is interesting to design with a low-cost machine. We know that if our pieces are printable with good quality in Ender 3, it will be possible to print it in better and more expensive machines.

    We also made a lot of prints to understood the limits of the machine, the tolerances and the capability to print. Here some important conclusions about the printing process with an Ender 3.

    1. If you want to print a piece that has to fit really tight, between 0.2 and 0.3 mm of tolerance is ok
    2. If the fit has to pass through and be gentle and soft we recommend 0.4mm or more
    3. It is important to be familiar with the tool, try and fail a lot, try to find the limits

    We also find these useful resources about the capability and configuration of the Ender 3 and Cura:

    https://all3dp.com/es/2/cura-ender-3-configuracion-cura-ajustes-perfil/

    https://youtu.be/BrnUIAvkn60

  • UVA Joint_V1

    Miguel Fernández07/18/2020 at 12:33 0 comments

    To achieve a multi-tool kit it is necessary to understand the parts of it. This system is composed of two main elements: The battery pack and the Instrument or tool (in this case the ultraviolet light for curing adhesives).

    It's a simple idea based on one challenge, the joint. This is also the most important mechanical part of the design because it is the starting point for the development of different tool-heads. The UVA joint has to achieve 4 principles:

    1. Simplicity (to encourage people to develop new tools)
    2. Durability (It has to resist the wear of daily connection/disconnection and also the falls and shocks)
    3. Reliability (the user should be confident that the electrical and mechanical joint wouldn't fail and the tool will work as it is expected)
    4. Replaceability (The modular design of the UVA system allow to replace the chassis where the joint is build in without affecting the electronics).

    With these bases in mind, we design a rotational joint that is structured by three different connections: the snap-fit cantilever, the electrical contact and the Locks. It is necessary to leave some tolerance (in our case 0.4mm) because FDM prints are not 100% accurate. Calibration, environmental conditions and human interaction could affect the quality of the finished pieces. We need a tight fit because we have to prevent movement between the battery pack and the tool, but also we need to prevent the plastic to fail, crack or to not fit at all.

    To fit the part it is necessary to make a 28 degrees rotation in the longitudinal axis. It will snap by this rotation and do not return to the starting point without some force. Every connection has its mission to constraint the parts together.

    1. Snap-fit cantilever: this part is the most complex to design and is the one that ensures that the UVA joint will keep together the battery pack and the tool. It makes a restriction in the rotation after the snap. This rotation restriction could be broken after applying some force to unlock the uva joint.
    2. Locks: This connection is responsible for avoiding the movement in the vertical axis. The locks will help to reduce or eliminate the forces over the snap-fit cantilever after the snap, increasing the quality of the joint and the durability of the connections.
    3. Electrical connection: This part is under development. It will be the mechanism responsible to transmit the electricity between the battery pack and the tool.

    The joint was modeled with Autodesk Fusion 360, here the link to the model: https://a360.co/2OywktE

    We are going to be using this software because it is free and tremendously good for mechanical design. It can also be use to simulate electrical circuits. 

    Here some information that we used to design the UVA joint:

    About conections:

    https://www.3dhubs.com/knowledge-base/how-design-snap-fit-joints-3d-printing/

    https://drive.google.com/file/d/1E7P1v8KytKME5-KJwtn3b6-2PuZkFO8J/view?usp=sharing

    https://drive.google.com/file/d/1D9oW7FTgxugsrYvvysp96yshwzoi6t6p/view?usp=sharing

    Snap-fit design calculator:

    https://plastics-rubber.basf.com/northamerica/en/performance_polymers/services/service_calculation_programmes.html

    About PLA:

    friction coefficient: 0.492

     https://www.researchgate.net/publication/330003074_Wear_and_coefficient_of_friction_of_PLA_-_Graphite_composite_in_3D_printing_technology

    Secant modulus: 3300 Mpa

    http://www.matweb.com/search/DataSheet.aspx?MatGUID=ab96a4c0655c4018a8785ac4031b9278

    Allowable material strain: 3%

    https://www.researchgate.net/publication/257608973_Enhanced_ductility_of_polylactide_materials_Reactive_blending_with_pre-hot_sheared_natural_rubber

  • Choosing the UV LEDs

    Said Alvarado Marin07/05/2020 at 11:58 0 comments

    LEDs come in all manners of sizes, colors and brightness. To be able to choose the most appropriate ones, we need to know what are they going to be used for. For this purpose, we did some market research on UV curing glues. After checking the datasheets of 89 models of adhesives across 4 different companies, we came up with following graph:

    The source of this information can be found in spreadsheet format, here.

    Let’s highlight some important aspects of this dataset:

    • Save for a handful of glues specifically designed to be cured by visible light. All studied adhesives can be cured by a wavelength of 365nm.
    • The large majority of datasheets recommend an irradiance of around 100 mW/cm^2 or less for ideal curing conditions. (Though the documentation can be somewhat ambiguous on the absolute minimum irradiation required to still cure the product).
    • Small portion of glues from Henkel recommend using a secondary wavelength of 250nm to improve curing on surfaces exposed to oxygen. We will not be addressing this, as it would prohibitively increase the cost of the project.

    From this information we can conclude that we should ideally aim for a lamp that emits 100 mW/cm^2 @ 365nm, as this gives the project the best coverage of commercially available glues. Though as we will soon see, it is not trivial to emit light at such high intensity from a battery powered device.

    SELECTING THE LEDS ON MOUSER/DIGIKEY

    It turns out there are not that many high power UV LEDs available in Mouser or Digikey. Even less when you search for ones that:

    • Emit at 365nm
    • Have high power and efficiency.
    • Are inexpensive.
    • Are readily available and well stocked.
    • Have small viewing angles (we need a concentrated beam light to reach those 100mW/cm^2)

    We decided on the IN-C39ATOU2 from Inolux, link to the Mouser listing here.

    Some highlight of the LED are:

    • Forward Voltage: 4.4V
    • Forward Current: 1Amp
    • Radiant Flux: 1600mW
    • Wavelength: 365 – 370 nm
    • Viewing Angle: 30°
    • Size: 4x4mm
    • Cost: 13.62 $ per led

    Note: Yeah, I know that they look really expensive. But the other were not much better. UV LEDs are just really expensive.

    HOW MANY LEDS DO YOU USE ?

    Ideally we don’t want to use more LEDs than absolutely needed, both because of the price, and to save on battery life. Thankfully the datasheet provides us with all the information needed to run a couple of simulations and figure this out. Namely, the total power emitted as light (1.6W) and the radiance pattern, which looks like this:

    Image source: IN-C39ATOU2 datasheet

    No we can program a small script in Python to calculate how this beam pattern would look projected over a surface, at different heights.

    From here we can see that at its peak, 6 LEDs can indeed generate the 100mW/cm^2 we were looking for, even if it just in a small point. Now let’s look at those irradiance patterns a bit more closely:

    At 7cm from the target, the center of the pattern surpasses 100 mW/cm^2, and there is a circle of about 2.4cm in diameter of light above 90 mW/cm^2. Not much in terms of area, but that’s quite an impressive power density.

    Now, if you’re working with glue that cures at lower energy levels and prefer less power over a larger area. At 25cm away, the six LEDs can generate a circle of 14cm in diameter with over 20 mW/cm^2. Which is rather respectable for a handheld battery powered device.


    CONCLUSION

    For a total electrical power consumption of 26.4W and around 81.72$, these LEDs seem like the most sensible choice for the job. They cover both scenario, focused high intensity UV light from up close for those glues that require it. And, wide area low intensity UV light from far away for when area coverage is more important than high intensity.


    EXTRA:  WHY NOT USE STANDARD 5MM UV LEDS ?

    Let’s explore a fair question that might be in your mind after reading this post. If you search on Amazon or Ebay right now for “UV LED”...

    Read more »

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Discussions

John Loefler wrote 07/09/2020 at 22:16 point

The only one I found. In my searches that has more power output is the

NVSU333A (https://www.nichia.co.jp/specification/products/led/NVSU333A-E.pdf)

  Are you sure? yes | no

Said Alvarado Marin wrote 07/14/2020 at 21:58 point

Hi John! I'm glad you liked the LEDs, it took a lot of investigation to find them. :)

The NVSU333A look really impressive, that's a lot of Radiant Flux in such a tiny package. Heat dissipation must be really tricky to manage in such a powerful LED though.

  Are you sure? yes | no

John Loefler wrote 07/07/2020 at 18:54 point

Good Choice on the Inolux LED.  Not only is it better than any lower powered array.  Because it is a single chip the output is a coherent.

  Are you sure? yes | no

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