LED Coaster - Wireless/Batteryless

A new take on the LED coaster with wireless power charging and supercapacitor energy storage.

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LED drink coasters are nothing new, but what about one that charges wirelessly and doesn't require traditional chemical batteries? When not in use simply place the coaster in it's charging base to recharge.

What is it?

LED drink coasters are nothing new, but this one is different than the others in more than just aesthetics. LEDs around the perimeter of the coaster rotate around, with one LED on at a time. This device can be wirelessly charged.

What is the goal of this project?

This basis of this project was to explore the feasibility and operation of a rechargeable device utilizing supercapacitors rather than traditional batteries.

What sets this apart from other LED coasters?

-Ease of use

  • Wireless charging allows for easy recharging. No need to plug anything in or replace batteries.

-Lessened environmental impact

  • Using supercapacitors means there will be no batteries that end up in landfills. Many LED coasters on the market generate a lot of waste in one-time use batteries.

-Slim and aesthetic design

  • The features of the PCB are the focal point of the aesthetics. Using supercapacitors rather than batteries allows for a slimmer design than other rechargeable LED coasters.


  • The coaster is hermetically sealed in casting resin making the device impervious to spilling liquid or condensation. The encapsulated design also protects the coaster components from drops.

Is it a product that could succeed in the market?

Though more expensive than some other options in the market, there exist features that justify a higher price point. The feasibility of such a product in the market would hinge on optimizing the design and production to bring the price to a desirable level.

What is planned for future revisions?

-Increasing energy efficiency.

-Decreasing cost by looking at more cost effective components and designs.

-Smaller, more customized footprint to allow for a slimmer design.

-Removing 3D printed coaster base, allowing the full coaster to be held in casting resin.

-Optimization of production process.

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  • Vishay Supercapacitors

    Scott Clandinin08/20/2019 at 06:00 0 comments

    The folks at Vishay were nice enough to notice my project and send me some samples of the same capacitor type I've been using for energy storage. This was quite fortunate as Digikey out of stock with a fairly long lead time. This will help me to be able to work on future iterations of the project, so big thanks to Walter @ Vishay.

    I was also linked to some documentation on the capacitors regarding efficient charging to maximize the lifespan and capacity of the caps.

    I haven't incorporated any of these best practices into the current project, but I will be looking into this on future revisions.

  • REV0 Video

    Scott Clandinin08/18/2019 at 00:48 0 comments

  • Production Costs

    Scott Clandinin08/11/2019 at 05:50 0 comments

    Optimizing parts, vendors, and process when planning to scale for production is no easy task. This years Hackaday prize is a good exercise for me as I've never looked at any project as a potential commercial project, only as a prototype as a hobbyist.

     I've come up with some numbers to get an idea of my cost per unit when I would be ordering parts for 100 units. This certainly won't be a final BOM, and some estimations are made, but will give me some kind of idea what the material costs would be.

    If I were to order parts to make another unit I would be spending around $35-$40 CAD. If I were to order parts for 100 units I would be spending around $15-$20 CAD per coaster. The most expensive parts are the supercap and the wireless charging coils and circuitry, making up nearly half of the total cost. Much more research would need to be done into these parts in order to find the best prices.

    If I were to make a second prototype the same as the first, there would be about 2 hours of labour involved. This includes hand soldering SMD components, starting 3D prints, pouring resin and clearing bubbles (and light monitoring), and assembling charging base. 

    Significant time would be saved by:

    -using a reflow oven rather than hand soldering all SMD devices (or even using a 3rd party PCB service to solder most of the components during manufacturing).

    -relying less on 3D printed parts, and more towards professionally moulded enclosures.

    -doing the processes with several units at once rather than doing one to completion.

    If brought this to market, a sticker price for this product could possibly be somewhere between $30-$40 CAD with the numbers I have currently.

  • Other LED Coasters on the Market

    Scott Clandinin08/10/2019 at 07:58 0 comments

    Below are a few examples of LED coasters that are commercially available. In addition to these, there are a handful that can be found on 

    FlashyBlinkyLights Infinity LED Coaster

    Cost for one: $5.30 CAD (price breaks available on higher qty)

    Device uses two CR2032 batteries (included). Price is good, but the major cost over a long period of time would be the batteries themselves unless those too are bought in bulk. It isn't described how long this can go until battery replacement is required, but likely multiple times a week. Coaster height not advertised.

    FlashyBlinkyLights Pressure Activated LED Coaster

    Cost for one: $5.30 CAD (price breaks available on higher qty)

    This is a pressure activated LED coaster. Device uses two CR2032 batteries (included). Price is good, but the major cost over a long period of time would be the batteries themselves unless those too are bought in bulk. It isn't described how long this can go until battery replacement is required, but likely multiple times a week if used regularly. Coaster height not advertised.

    Glow Products LED Coaster

    Cost for one: $2.90 CAD (minimum qty of 6 required)

    Another pressure activated LED coaster. Device uses 3 AAA batteries (not included). 24hr of continual use between battery changes. There would be a large cost in batteries for regular use. 20mm coaster height.

    Brag Gear Retro Lights LED Coaster

    Cost for one: $19.99 CAD (price breaks available on higher qty). 

    Device uses two CR2032 batteries (included). Battery life likely below 24hr. 4mm coaster height.


    Most LED coasters out there are quite cheap when you don't consider battery purchases. Regular commercial use of these coasters would add up in price and environmental impact with regular replacement of multiple batteries per coasters.

    A smaller number of coasters out there have direct DC power connections or include a USB port for charging a rechargeable battery.

    From my search, there does not appear to be any LED coasters out there (commercially available at least) that are either wirelessly charged, or uses capacitors for energy storage rather than traditional batteries. The following benefits of my design may be enough to justify a higher price point:

    1. Easy wireless charging.
    2. No continual battery purchases. Smaller environmental impact as there will be no batteries or battery packaging that will end up in a landfill.
    3. Hardier design than competitors (fully sealed and protected from moisture).
    4. Aesthetic design displaying circuitry.

    I will be reworking my BOM pricing based on buying parts in bulk, and some redesigning to be able to use less supercaps. The the project log will go over the cost to manufacture and a possible sell price to compare to existing coasters.

  • Slimming the Coaster

    Scott Clandinin08/09/2019 at 23:24 0 comments

    The next stage of the design will also be focusing on making a thinner coaster.

    The coaster is about 11mm high. About 8.5mm of this is the 3D printed base, with about 1.5mm rising above the base for the curved finish of the resin.

    With some rearranging and recessing, I can bring this total height down.

    1. The potentiometer in the top left will be replace by a SMD resistor. I only included a pot in so I could test at different clock speeds.

    2. The coil receiver circuit board can be removed and the components can be designed into my circuit board. The leads from the coil will be shortened to keep them low to the board.

    3. Similar to the cut-out for the coil in the middle, I can leave a space for the supercaps to be recessed in as to not add height. 

    With this arrangement, the highest component would either be the LEDs (2.1mm) or the inductor (TBD). I'll be safe and assume the highest component will be 2.5mm from the board. The calculation for a rough total height would be:

    3D printed base + PCB thickness + highest component + resin overhang

    0.7mm + 1.6mm + 2.5mm + 1.5mm = 6.3mm

    With these design changes I would able to decrease the height by 4-5mm. 

    Besides the better aesthetic of a slimmer coaster, it would also use a bit less casting resin and 3D printed material. The 3D printed material cost is mostly negligible but a decrease in print time would decrease the overall bulk manufacturing time if I were ever to try to scale up production.

  • Drawing Less Power

    Scott Clandinin08/08/2019 at 06:28 0 comments

    The first prototype is complete. With the next revision I will aim to minimize the current draw to extend the time. If this were to become economically feasible, I will need to use less super caps, possibly down all the way to just one 15F.

    Run Time Extending Changes:

    -rather than have my output of the regulator at 2.75V I can increase that to 2.8V (voltage rating of supercaps).

    -adding a diode between the output of the regulator and the caps will ensure that no current flows back through the regulator circuit when the supply is removed. The resistor divider network in the regulator would draw a little over 2mA passively. With a diode in place there is no way for the caps to back-feed into the resistors.

    -using a lower power timer/osciallator. My 555 timer has a listed current draw of 250uA, while there are some available I've seen that are listed as low as 50uA.

    -use LEDs with a lower current draw and 1.8V forward voltage.

    A Hackaday user also recommended a buck/boost converter to use to bump the voltage back up once it falls below a usable value. This is something I will look into as well.

  • First Video Demonstration

    Scott Clandinin08/06/2019 at 03:57 0 comments

  • Turning it into a coaster

    Scott Clandinin08/02/2019 at 02:43 1 comment

    The board was complete and working, the next step was to actually turn it into a coaster. Rather than use a piece of glass or acrylic, I wanted to pour in a clear resin to give it a smooth and seamless finish.

    I used art casting resin for this. The way this resin is used is by mixing a resin in with a hardener and pouring in. It was a self-leveling fluid, so all I needed to worry about was putting it on a level surface.

    In order to have a clear finish, a lighter or torch must be used on the surface of the resin to bring the air bubbles to the top. A small torch would have done the best job, but I used a lighter as I had it on hand. Care needed to be taken with how long I applied heat to the resin solution, as too much heat could cause damage to the electronics (the insulation on one of the caps was slightly melted). It's key to stay on top of bubbles, as new bubbles will arise even up to 30-40 minutes after the pour.

    I would have had a clearer finish with a torch, but the result was decent, albeit a bit cloudy. An error I made was not applying the lighter heat until several minutes after the pour. I waited longer than I should have for it to self-level and clear some bubbles on it's own. After pouring there is only a fairly small window of time before the solution begins to harden.

    The imperfections are noticeable up close, but from a distance the coaster still looks great. I will took what I learned from this first pour into making the second coaster more clear.

  • Coaster Enclosure and Charging Base

    Scott Clandinin08/01/2019 at 04:38 0 comments

    From left to right: Coaster body, charging base top, charging base body, charging base bottom.

    In future versions the charging base will have a more aesthetic design, but this will suffice for now.

  • Capacitor Storage

    Scott Clandinin07/03/2019 at 05:50 0 comments

    Current Draw

    With two sets of stacked super caps, the total storage is brought to 60F.

    The below is the current draw of each major component. This doesn't encapsulate everything, especially with changing supply voltages, but it is a good show of how the LEDs have the majority of the current draw.

    555 Timer: 0.25mA

    4-bit binary counter: 1uA

    4-16 bit decoder: 8uA x 2

    Single LED: 27.5mA

    I selected the regulator to be 2.75V (just under the 2.8V rating of the caps). Since the forward voltage of the LEDs is 2V, this device has a useful range of only 0.75 volts. Once below 2V, the LEDs will no longer light up and the device will slowly bleed out the remaining energy.

    Charging Time and Run Time

    Upon powering the device with the charging coil, the caps quickly charge to 90-95% of the max voltage. I originally thought this was "close enough" to being charged. When removing from the supply after less than a minute of charging, the device would run out of power within a very short period of time. 

    Charging it for longer and monitoring it shows that the voltage quickly ramps up, but flattens out near the peak and takes quite a while to actually reach 2.75V. When giving it a long time to charge completely, the device was able to run for about four hours.

    Possible ways to increase run time:

    -increase supply voltage (limited by capacitor specs $$$)

    -more capacitance ($$$)

    -choose LEDs with lower forward voltage

    -run LEDs dimmer (larger series resistance)

    -find a timer with lower current draw (if available)

View all 13 project logs

Enjoy this project?



string0fellow wrote 01/28/2022 at 10:49 point

This is really cool and similar to a project I've been working on. Adding a reed switch to turn the device on and off could be a useful feature to add and could even be used to with a microcontroller to switch between preset patterns.

  Are you sure? yes | no

k1200s wrote 04/07/2020 at 07:52 point


I'm looking forward to make this project.

But there are some doubts:

- both In the schematic and the PCB there is a potentiometer, which in the BOM does not appear;

- there is a 12k resistor in the BOM that does not show anywhere in the schematic;

- the inverter gate 296-18657-1-ND (U4) in the schematic is necessary? In your PCB images it is not present;

- what is the package size of the LEDs?

- can you please share the STL files for the base charger and for the epoxy resin mold?

  Are you sure? yes | no

Scott Clandinin wrote 04/08/2020 at 05:04 point

Hey there, cool to hear you're giving it a shot!

-the pot isn't really necessary. I had it in there to play around with how fast the LEDs cycled, and found it was best slowed down as much as possible. I used a thru-hole 10k pot (~7mm wide and long), but if I were to do it again I'd just use a similarly sized resistor between holes 1 and 2 of the pot.

-the 12k resistor would be to replace the pot. I brought it up slightly as I figured the LEDs should cycle a bit slower than they do now on a second iteration.

-the inverter is necessary to be able to enable and disable each decoder. since I'm using two 3:8 decoders to get a 4:16 decoder. On a count from 0-7, U5 will be in control (the 0 value of QD will be inverted to enable U5). Once the count reaches 8, QD enables U6. It is present on the PCB, but just very tiny (U4 designation).

-package size is 3528 metric or 1411 imperial. I can't recall though if I picked this as a standard size in kicad or if I did custom footprints with the dimensions recommended in the datasheet. New PC and I don't have that installed yet to confirm.

-on the left side of the page there is a link for "Enclosure CAD files"

Don't forgot to put the diode in between the charging module and the voltage regulator as that isn't on the schematic/PCB. Without this the capacitors backfeed into the module and waste energy. I'd also recommend using one of those kitchen torches instead of a barbecue lighter which I used. You'll get far better results than I had. Just make sure you don't melt the caps (which I did slightly hah).

Let me know how it goes and if you have any other questions, as the design is still fairly hacked together.

  Are you sure? yes | no

k1200s wrote 04/13/2020 at 01:26 point

Hi Scott,

thanks for your help!

I've already ordered the PCB and some of the components. Now I'm searching for a supplier for the epoxi resin.

Let me ask you two more things:

In the image that you've posted with the coaster on a table, still with the green mold on, it seems that the transparent surface is not really flat as it should be, it seems that the resin solidified bending slightly downward near the borders of the circle. If this is true, wouldn't it be solved printing the mold a bit taller? Or with a resin type more fluid (or less viscous)?

As for the mold, do you think that it could be used more than once? I probably will make more than one coaster, if I could use the same it would be great!

Best wishes,


  Are you sure? yes | no

Scott Clandinin wrote 04/13/2020 at 20:34 point

Hey, for some reason I can't reply to your latest reply.

The rounded edges was intentional to give it a smoother "rounder" feel. If you wanted yours perfectly flat increasing the height of the mould would be the right call. For my own preference I wanted to have it come a bit over the mould for aesthetics and to make it it look slimmer than it actually is (than it would be with a deeper mould). I used ArtResin which is very viscous but self levels quite well. A mould with a 3d printed part would be permanent, of if you did get it off it wouldn't finish well by nature of all of the small edges since the 3d printer can't create a totally smooth circle.

Have a skim through the video below though (if you can stomach the peppyness hah), here they use a flexible and totally smooth mould. That would work for reusability, though I don't know where you could get your hands on or make something like that.

  Are you sure? yes | no

k1200s wrote 05/09/2020 at 03:37 point

As the circuit has no on-off switch and no other way to physically interact with it once encased with the epoxy, how can we turn it on and off?

Does it turn on automatically since the capacitors have been charged and will remain on untill are discharged?



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Tom Nardi wrote 08/10/2019 at 03:28 point

I wonder if you could eventually do away with the 3D printed bottom piece, and just cast the whole thing directly into the resin using a mold. Something like this:

Would save printing time, and potentially allow you to shave off another millimeter or two.

  Are you sure? yes | no

Scott Clandinin wrote 08/10/2019 at 05:07 point

Hey Tom, thanks for the link. This is something I have thought about but kind of left on the backburner, so I'm glad you brought it up. When doing research on the kind of casting resin to buy I came across an example of them making coasters from molds that came out pretty nice.

You have a great point that it would save a lot of manufacturing time and would probably look way cooler to be able to see everything from any angle. It may also shave off a bit of height as well, but not too much overall as I would likely pour a tiny bit of resin the bottom of the mold to harden before the PCB would go in so I would have a smooth bottom. The way I cast the prototype was with the PCB already touching the bottom of the 3D printed enclosure before pouring, so I may lose a bit of the height saved getting rid of the base. Still, definitely worth going after for future revisions.

Also, I thought I recognized your name, I enjoyed the article you wrote on the project. It definitely inspired me to continue improving it. If you saw my last project log you can probably tell that I stole your idea to bring the supercaps into the board similar to the charging coil to bring the height down hah. Thank you kindly for those and this latest suggestion!

  Are you sure? yes | no

George Zimbru wrote 08/06/2019 at 15:10 point

Scott, neat project.

Suggestion if you want to add a remote connection (paging capability), you could use the trigboard (Kevin Durah) due to its really small current draw when in sleep mode.

Also adding some cork board inlaid above the inner charging ring would be awesome for making sure the condensing water gets absorbed and doesn't get on the surface the coaster is trying to protect.

Pretty cool implementation.

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Scott Clandinin wrote 08/07/2019 at 04:23 point

Appreciate the tips, will keep those in mind!

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offtherails2010 wrote 08/05/2019 at 22:48 point

hi Scott, 

well done on this project, its truly beautiful !! Gorgeously made PCB and Casted Acrylic Resin just makes things like this even more so-beautiful !!!

As for a Lower power timer IC, the 555 Timer also comes in a really tiny SMD package of a hair split less than 1.43mm × 1.41mm and just under 0.575mm in Height !!! lol

Of course, its a BGA, but once one gets their head around how to solder BGA parts if one ALREADY Solders SMD Components with a regular soldering iron/hotplate & solderpaste methods, its relatively easy to do and practice makes perfect as with all things :)

LMC555CTP/NOPB (Just beautiful !!!)

TI Datasheet;

This sized device im sure could be a strong contender to having this specific IC and lower power consumption. Although i wasnt able to identify exactly how low power this package is, the only thing i could find was power dissipation of 568mW...

A hot-plate can simply solder it with solder paste if your doing the soldering yourself, there are far more efficient ways to solder which im not gonna go into here, just wanted to share the SMD Timer IC Size for ya :)

  Are you sure? yes | no

Scott Clandinin wrote 08/06/2019 at 03:58 point

This type of suggestion is exactly what I need, anything to bring down the footprint. Thank ya!

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David wrote 08/05/2019 at 19:59 point

Hi, a very interesting project.

One question.  I have counted 16 LEDs, which draw 16*27.5 mA = 440 mA.  Can your circuit run during 4 hours with a 440 mA load?

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Scott Clandinin wrote 08/06/2019 at 03:56 point

I have circuitry set up such that only one LED is on at a time. I just put up a video demo of it.

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conrad.farnsworthsci wrote 08/05/2019 at 19:56 point


I like the project. It's a great way to make a fully enclosed system. A couple suggestions though,

1) You're using a linear voltage regulator. These are absolutely fantastic for projects that get continuous power. Otherwise, they waste a terrifying amount of power just stepping the voltage down ((Vin-Vout)*CurrentIn). Once the voltage on your caps dips below the drop-out voltage your regulator will shut off. I would suggest a buck/boost converter to buck the voltage down when the caps are above Vout. This will automatically switch to boost mode to bump Vout up once the caps dip below Vout allowing you to squeeze even more life out of your project. Plus they're typically ~80% efficient, compared to 50% efficiency of linear regulators.

2) Your binary counter/decoder scheme is neat, but you could replace the whole thing with a decade counter. 

3) For more control, I would suggest an ATTINY85 and 2 8-bit shift registers. This allows you to program in PWM for fading, and more patterns. It's also the size of the 555 timer you use and uses about 300uA at 1.8V. 

4) Now that you own the wireless charging board, you should be able to get an example schematic from the chip manufacturer and integrate that directly on to your board. 

5) As you mentioned above, the LEDs you're using are using considerable amounts of power. Here is what I use: APT2012LZGCK. They eat about 10x less current than the ones you are using and are visible in direct sunlight. 

I hope this helps.


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Scott Clandinin wrote 08/06/2019 at 03:35 point

Hey Conrad, love the ideas. Thanks for the suggestions!

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Gerben wrote 08/06/2019 at 15:45 point

4b) You might even be able to create the coil on the PCBs copper layer. Similar to what bobricius does on

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Mark Edwards wrote 08/05/2019 at 19:13 point

Hey,  Like the project.

You could remove the NOT chip and feed E1 & E3 with the same input signal and one less chip to feed.

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Scott Clandinin wrote 08/06/2019 at 04:01 point

Good shout, I will look into that.

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karthik ram wrote 04/25/2019 at 06:53 point

Hi! I working on a robotics project... Check it out! Do drop a like too :P

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