Terrarium With Wirelessly Powered Lights

Intro

I love the idea of terrariums both the fact that they are completely enclosed little ecosystems, and that they can look like miniature landscapes, kind of like Bonsai without the years of effort!

My kids of 6 and 4 have become enamored with them too, and I love it because it is a wonderful excuse to take a walk in the woods, collect some bits and then do a bit of crafting.

This is my attempt to add an extra element of magic, by adding lights to the scenery that never need batteries or require the lid to be opened, via the wonder of wireless power transfer! Thanks to the Instructables Mason Jar Contest for giving me the kick to get this project done!

Parts

• Mason Jar or similar (the clearer the better)
• 3D Printed Base (We'll design and 3D print this to match the jar)
• 5V 3W Led Module
• Wireless Power Module
• USB Cable and Phone Charger (details on the electronics step)
• Something to light (lighthouse, cottage, robot, you use your imagination!)

Tools

• Soldering Iron
• Wire Clippers
• Hot Air Gun (for heat shrink)
• Hot Glue Gun
• 3D Printer (but you could make the base with other tools)

Consumables

• Hot Glue
• Wire
• Solder
• Paint (perhaps)

Terrarium Components

More details on this in the step, but in short

• Moss
• Stones
• Substrate

How It Works

The electronics for this project are remarkably simple (at a modular level) despite the results seeming a little bit like magic!

1. A normal USB port (or cellphone charger) outputs 5V
2. The wireless power module takes in 5V on it's input and converts this into an alternating current with which the transmitting coil is energized, creating a fluctuating magnetic field.
3. When the receiving coil is placed in the fluctuating electromagnetic field created by the transmitting coil a current is induced in it.
4. The receiving module converts the induced current back into DC and regulates it to the desired output voltage (5V in our case)
5. The LED module is powered with this 5V supply

Wireless Power Module

I used this Wireless Power Module

This module is the foundation. You will probably be able to find a few other options, but I do recommend using one that has a 5V input, since it make it much easier to power the whole project off USB (and therefore an old phone charger)

The module I chose claims to be able to transfer 2A, but a few LEDs will be nowhere near that (and with the large gap between the transmitter and receiver it is unlikely that we would achieve such a high current anyway)

LED Module

I used this 5V 3W Led Module, but you can power whatever 5V device you like, even just some regular 5mm LEDs with the appropriate resistors (a string of fairy LEDs on a little tree could be super cute!).

I tried this module because it looked super bright, the fact that it didn't need any external components was a bonus. It also has a transistor on the board, meaning I can easily tie it to a microcontroller in the future if I want (or an LDR to turn the light on only when it gets dark).

For now I just tied the "signal" line (i.e. the transistor's base) to VCC/5V to enable it.

I measured only 200mA at 5V which, so nowhere near the advertised 3W, but good enough.

Socket and Cable

I salvaged a USB-B Socket off an old Arduino, but if you don't have that sort of thing lying around then you can try something like these female sockets (which are handily labelled too) or perhaps these bulkhead USB socket

When you are designing your base you will need to take a socket into account.

Connectors

One thing worth thinking about is how you are going to assemble this thing in a jar, and hide it among rocks and vegetation.

I thought I was being very clever by adding an XT30 connector in between the LED and receiver, chosen because of it's nice firm water resistant connection, but it was very difficult to assemble with one hand in the jar!

One key element of a healthy terrarium is constant humidity, unfortunately this is also pretty much the worst environment for electronics.

I chose to waterproof the receiver module itself, while allowing the coil to rely on its insulation (and simplicity).

Time will tell just how robust this turns out to be, but the components were cheap enough to experiment with, and I am nothing if not curious.

Hot Glue

I built up a big blob of hot glue one the cables on either side of the module, bit by bit, rotating it all the while like a glass blower, to prevent it dripping.

Once the hot glue had set I slipped over a large piece of heatshrink and heated the two ends, making sure that it bonded with the hot glue. I chose not to apply heat to the center of the heatshrink, to prevent applying any pressure on the module itself.

Silicone

I used marine silicone (as used to build aquariums) to bond the receiving coil to the base of the jar. In my experience hot glue doesn't bond well to glass.

One could waterproof the electronics with silicone, but many types of silicone are very corrosive to electronics.

Make sure that you get the coil in the right place! It is best to have the circuit active so that you can find the point that makes the LED the brightest.

Goal

In order to get the most efficient power transfer it is important to get the transmitting and receiving coils as close to each other as possible, and the glass already enforces a large separation. The module is only specified to run across 3-6mm separation after all.

We could assume that the base of the jar is flat and design a base accordingly, but the coils would end up a good few millimeters further apart than necessary.

Measuring a Tricky Shape

I did some very simple measurements of the base of the jar, using only a metal ruler, sketched those on paper and then recreated them in Autodesk Inventor (you could use Fusion360 in exactly the same way). I extruded this profile to 0.6mm thick and 3d printed it. This print should only take a few minutes.

By comparing this flat profile to the jar (you could 2D print and cut out of paper too, but this seemed easier) it only took me two revisions to get a really good fit and cost almost no filament.

Once you have tweaked this profile to your satisfaction, save it, because we will use it to create the base too!

Base Shape

In the previous step we created a perfectly fitting, and tested, profile to be sure that our design would fit the jar perfectly, so we can dive into this large(ish) print without any worries of wasting filament.

Simply use the revolve operation on your profile instead of the extrude and you will have the perfect base.

Wireless Power Module

The recess for the wireless module is a simple circle. I created a surface 0.8mm from the top of the base and extruded a cut up to it, in order to get it as close to the jar as possible.

Power Connector

I salvaged a USB-B female socket off a dead old Arduino, so I created a suitable rectangular recess for it in the base.

Hand Made, Just Like Grandpa Used To Do It

If you don't have a 3D printer, it should still be totally feasible to do this project with good old fashioned hand tools.

So long as you can use a non-metallic material, and get the transmitting coil as close to the surface as possible you should be good to go.

Pre-made

Another interesting option (but buyer beware, I haven't tested these), would be to buy one of these nice looking Qi Wireless Charging bases, and a matching receiver. Here are some options, but I recommend you read the specs carefully!

Wood Grain Wireless Charging Base

Wireless Charging Receiver (USB C output though)

Wireless Charging Receiver Circuit

Now comes the fun part!

You will need to find a decorative item to put in your terrarium, one that can somehow accept a little light-up element.

I initially was planning to design my own lighthouse, but somehow managed to overcome my obsession with designing everything myself and chose to use this little cottage instead. It is in fact just a small section of a wonderful set by Pasquale Belvito which you can find on thingiverse here.

Finding something that is easy to access the innards of is going to help. Remember you will be assembling this in a jar!

Printing & Painting

I printed the base and the roof both out of PLA on my Sindoh DP200. I roughly dabbed on some acrylic hobby paints after laying down a base coat of satin black Rustoleum Paint & Primer.

No 3D Printer?

If you don't have a 3D printer, no worries, how about a pretty dead tree with fairy lights? Or find a decorative lighthouse in a thift-store?

Enjoy Nature a Bit

One of the best bits about building these simple jar terrariums is that my kids love to get involved and to collect their own vegetation to build their own. What a glorious excuse to wander about in nature and appreciate the littlest bits of it.

Learn from the Best

Before I go further I should note that I am no botanist, and if the tiny garden dies we shall count it as part of the experience and build it again. If you want the input of a real master I highly recommend watching Serpa Design on YouTube

In fact, here we go, this one suits our build perfectly. Thanks Tanner!

The following are the layers, working from the top down, of elements that I have included in my terrarium.

Accent Elements

In my case this was just a big freakin' cottage with a LED in it...

Vegetation

The vast majority of our terrariums are populated with moss, which is easy to find (and surprising in its diversity).

We have also inserted small grasses and ferns, which have had varying degrees of success.

Substrate

Basically this is a collection of dirt, bark, small stones etc. which I would previoulsy have called soil, but apparently that's not the done thing in terrarium talk.

Stones

This bottom layer of stones is supposed to allow for good drainage, so that the water does not become stagnant. It also makes a nice visual impact, since it looks like we are looking at a cross-section of the earth.

Activated Charcoal

I didn't have any of this, and didn't use it. The idea is that it will help to filter the water that makes it to the bottom of the terrarium, helping to prevent it going stagnant. All the experts recommend it, so it is probably worth tracking down if you aren't trying to build in a week to enter an Instructables contest...

Well, that's it really.

This project was an absolute blast, and it was the Mason Jar Speed Challenge that inspired me to get it done and documented within a week of stolen moments (which means its a great weekend activity with a little planning ahead).

If you appreciate it I would love a vote in the contest, but either way, thanks for reading to the end!