Beach Buddy: 3-in-1 Solar Phone Charger, Boombox, and Sunburn Timer Calculator

Imagine the ideal beach trip. The sun is shining, the skies are blue, the water is warm, and the humidity is low. You and your friends have everything you need to soak up the sun, sand and surf: a cooler filled with drinks and snacks, sunblock, flip flops, the coolest new swimwear, and the newest beach tech: the beach blanket/towel with corner pockets to fill with sand so it won’t blow away; the sun shade with privacy screens and sand-fillable anchors for ultimate beach sheltering, even the spiked drink holders that keep your frosty beverages upright and sand-free.

Beach Buddy

But what’s a summer day without a summer soundtrack? Good thing you’ve got your tunes on…your…very expensive…and very vulnerable to the elements…phone…hmm. Well, you do have that waterproof phone case with speakers, but it’s bulky, ugly, and doesn’t have a hole through which you could connect the little solar charging panel you bought (for when that fickle phone battery goes dead). Huh.

Well, while you’re musing on what to do, don’t forget the pain-relieving aloe gel in your cooler, for those inevitable sunburns. You’re not keeping track of the time since you applied your sunscreen, admit it. You’re just gonna burn. Might as well have the aspirin and Lidocaine easily accessible anyway. Enter the Beach Buddy. It’s an all-in-one, water- and sand-resistant, solar charger, audio speaker system, and sunburn timer calculator.

This Instructable harnesses the power of Arduino, a UV sensor, and simple mathematics to make one nifty gadget sure to boost your outdoor summer fun – and minimize your indoor summer recovery!


For my Digital Multimedia class’ final project, we were instructed to develop “a proposal for a new product, new iteration, a “masterful and well-crafted kluge”, etc. of technology and interface” in the categories of apparel/fashion, toys, tools, furnishings, and/or art.

My mind instantly flew to something having to do with sun protection, because of the horrible sunburn I suffered on the first day of class – even though I’d applied sunscreen before going to the beach that day.

What had happened? Had my sunscreen expired? Not at all – it wasn’t as evenly applied as I’d thought, for one thing, but also I was in direct sun for far longer than my SPF was meant to be.

The World Health Organization has well-documented explanations for the UV Index, and the Skin Cancer Foundation goes into detail about both sunscreen sun protection factors (SPF) and the Fitzpatrick scale, a Harvard-developed system for classifying skin tones.

BUT WHAT DOES IT ALL MEAN?! And who has time for the WHO, the UV, the SCF, and the FPS?!

It all boils down to a simple formula. Once you know your Fitzpatrick scale type, you can calculate how long you can stay in the Sun without sunscreen before sunburn. Then divide that number by the current UV Index rating. Then multiply that quotient by your SPF rating – and your product is your allowed time in the sun before SPF reapplication is necessary.

So, in equation form: (Skin type time to burn ÷ UV Index) x SPF rating = time before reapplication of sunscreen.

The Beach Buddy does all this math for you with a few button pushes. Simply tell it your Skin Type and the SPF, and it’ll read the UV index and spit out your timer calculation!

SO NOW, without further ado, let’s get started on the Beach Buddy!

Step 1: Gather Materials

Note: the list below is rather exhaustive, and includes every last tool and supply I needed to make this project. Also note, my preferred supplier is Adafruit Industries, as it is a female-run company in a male-dominated field. Feel free to search for similar or equivalent products from alternate suppliers!

Materials – Project-Specific

  • 4x 10k ohm resistors
  • 10mm insulated standoffs (2 packs)
  • 2.1 mm DC Barrel plug > Alligator Clips
  • 9V Battery > 5.5mm/2.1mm plug
  • Acrylic sheet (thin)
  • Analog UV Light Sensor
  • 4x Breadboard-friendly momentary pushbuttons
  • Cable: 3.5mm Stereo Plug > Pigtail
  • 3x Cable: JST-PH Battery Extension
  • Enclosure
  • F/M jumper wires (1 pack)
  • LCD screen, 16×2 characters
  • 2x Lithium ion polymer battery – 3.7v 2500mAh
  • M2 screws, nuts, and washers (1 pack each)
  • M3 screws, nuts, and washers (1 pack each)
  • Mini adhesive-backed cable clips (1 pack)
  • MintyBoost Charger Kit
  • Nylon spacer (M2) (2 packs)
  • 4x Panel-mount momentary push buttons
  • PCB with connecting pads
  • Solar Charger Kit
  • Solar panel
  • 3x SPST Rocker Switch
  • Stereo Audio Amplifier
  • Stereo enclosed speaker set
  • Velcro strip
  • Wrapping wire (30AWG)
  • Optional: rub-on letters

Materials – Standard

  • 22AWG Wire, 3 colors each of stranded and solid
  • Breadboard
  • Cable Ties
  • Desoldering braid
  • Heat shrink tubing
  • Low-tack (painter’s) tape
  • M/M jumper wires
  • Solder


  • Acrylic cutter
  • Arduino w/ USB cable
  • Calipers
  • Center punch
  • Cork-backed ruler
  • Dremel with cut-off-wheel attachment
  • Drill
  • Flush cutters
  • Glue gun with glue sticks
  • Heat gun
  • Needlenose pliers
  • Precision needle file set
  • Precision screwdriver set
  • File set
  • Soldering iron
  • Step drill bits
  • Tabletop vice
  • Third-helping-hand
  • Wire stripper

Download the attached .zip archive for the above list in 1) product-linked spreadsheet, 2) product-linked webpage, and 3) unlinked printable PDF form.

Beach Buddy schematic

Step 2: Assembly – Charger

If you’re using parts from Adafruit, you’re in luck! Both the “solar charger” and “boom box” portion of this Instructable are derived from Adafruit tutorials. (If you’ve chosen other suppliers, the process should be similar.)

Assembling the Charger

  1. First, read through the Solar Charging Handbag tutorial HERE.
    • This is HUGELY IMPORTANT TO DO. While the solar charger procedures require very little modification, the MintyBoost charger should not be fully assembled. Notes below!
    • You’ll be following this tutorial up until the “Mint Tin Enclosure” stage.
  2. Now, follow the steps HERE to assemble the solar charger.
    • Bend the huge capacitor over before soldering it to the board, so it’ll lay flat inside the enclosure (as described here, and depicted in the first image above).
    • I followed Method 2 (stripping and soldering the wires together) to attach the solar panel to the charging cable. I cut the alligator clips off the DC-to-alligator-clip cable, and installed the DC barrel jack to the solar panel.
    • I chose not to install a thermistor or charge LEDs as mentioned in the PDF below; however, doing so would not negatively affect the Beach Buddy. Simply plan a spot for LEDs to be mounted on the project enclosure.
  3. Next, follow the steps HERE to mostly assemble the MintyBoost charger.
    • Solder on the JST battery cable that came with the solar charger instead of the battery holder (as mentioned here, and depicted in the second image above).
    • Lay down the tall capacitors and boost converter before soldering, too, as mentioned in the link/shown in the image above.
    • Ignore the instructions for incorporating the mint tin/housing the MintyBoost charger, since we’ll be placing our device inside a larger enclosure.
    • Do, however, hang on to the double-sided tape included with the kit! We’ll need it to attach the MintyBoost circuit board to the project enclosure.
  4. From Adafruit: “Plug the MintyBoost into the LOAD port on the solar charger, and plug a lithium polymer battery into the BATT port. Test [with a multimeter] that your MintyBoost is putting out 5 volts, then unplug the MintyBoost and solder on the USB jack as instructed.
  5. All your cables and circuits should be detachable at this point. You should have something very similar to the third image above on your work surface, only with a USB jack attached to the Mintyboost board.
  6. Test your work! Plug your cell phone charger cord into the USB jack, the battery, Mintyboost, and solar panel into their proper ports on the solar charger, and take the assembly outside. You should see your phone’s battery icon change to indicate it is in the process of charging.
  7. YAY you’ve completed approximately 1/6th of the Beach Buddy!

Images (abc) borrowed from the Adafruit Learning System under a Attribution-Sharealike Creative Commons License.

Download the attached .zip archive for the Adafruit tutorials in PDF form.


For more detail: Beach Buddy: 3-in-1 Solar Phone Charger, Boombox, and Sunburn Timer Calculator

About The Author

Ibrar Ayyub

I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough research and presenting information in a structured and logical format.

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