After cutting some 5mm acrylic sheets I watched how the light broke alongside the edges of those pieces. The light and the shapes of your surroundings change and shift like when you see someone standing in the water and suddenly the legs are off to the side of the persons upper body.

I wanted to make a lamp that makes use of that effect so I made a rough sketch of how that lamp might look like.

The sheets of acrylic would be stacked ontop of one another and some rods would prevent the sheets from sliding around. Those rods would also act as part of the user interface so that one could touch the bare metal at the top and change say the light intensity or switch general modes of the device. The rods would also mechanically hold the hole thing together top to bottom and they would attach to the electronics housed in the bottom section of the lamp.

The acrylic sheets would have a cavity in the middle for the light source which would be spiraling up around some sort of tube. In order to spread the light somewhat randomly I designed a simple zig-zac pattern along the perimeter of a circle. If the thing would need a battery then there would be some room in the tube to house it.

Fusion360 sketch

Some days later I fired up Fusion360 to create a 3D model from the sketch in my notebook.

TODO: Screenshot of the cross section 3d sketch TODO: Screenshot of the rendered small lamp

The (explosion of) features

This device is first and foremost a lamp but since I wanted touch button functionality, I knew that the brains of the device would have to be an ESP32, rather than an simpler ESP8266.

The fact that I would use an ESP32 lead to some extraneous features finding their way into the device:

  • Light source: 12V LED Strip
  • Secondary RGB light source
  • Three rods acting as touch inputs
  • Temperature and humidity sensor via I2C
  • Additional temperature sensor using OneWire
  • Light sensor for measuring the ambient light when turned off
  • Charging circuitry plus a magnetic charger port
  • On Off switch to (sort of) completely turn the device off
  • Battery voltage sensing
  • Four button 433 Mhz remote control
  • Last but not least a radar chip which allows the detection of movement within around 5 meters

Mechanical design

The mechanical design was done from the inside out. I was looking around for a tube that would hold at least one 18650 lithium-ion battery. In turn the tube defined the inner diameter of the acrylic disc and finally the rods and some spacing defined the outer most and thus the final diameter of the lamp itself.

The outer diameter plus some padding for the enclosure defined how big the pcb can be residing inside the cavity inside the bottom part of the lamp.

The height of the lamp had to be more than the length of a 18650-sized battery and was finally somewhat higher just by the fact how long I cut the tube. The height of the lamp is essentially variable since the tube, the rods and the spiralling LED strips can be extended upwards as much as desired.

TODO: Add screenshot of ridicilously high lamp for fun.

The M6 bolts were later replaced by less chunky, custom made 4mm brass rods. To one side of the rods I added a thread so that they could be bolted right onto the PCB using an M5 nut and a spring washer.

TODO: Picture of the rods

Electronics

For powering the LED I needed a boost converter and I had some that can also charge the battery. I figured out that I could “hijack” the Enable pin of that circuit in order to switch the 12V and thus the lamp on and off. This also lets me dim the LEDs using pulse width modulation (PWM).

For practical reasons I decided to use a Lolin32, which has a battery plug. It could also charge the battery, which is actually not relevant since the step up converter does alredy do that.

I added a Jumper for choosing to power the power hungry radar circuit from the battery or via cable through the magnetic charger inlet. Also there are some mounting holes which would later be used to hold the inner tube in place.

Both led strip are connected via regular 2.54mm headers. It is important though that they are outside the perimeter of the tube so I made sure to mark the diameter of the tube on the PCB.

For the first pcb prototype I would use a single side pcb with the traces being carved out using a 0.8mm pcb milling bit.

TODO: Screenshot of the schematics design TODO: Screenshot of the PCB design

The finished PCB looked like so:

TODO: Screenshot of milled PCB

Since I tested the main components of the design already on the bread board and made some adjustments there, I was confident that the circuit would work reasonably well.

Generally for me it turned out to be a good practise to start with a schematic design and document what I am testing on the bread board from a very early stage on.

Assembly

Using the rods and the PCB I would now start to assemble the device, laser cutting acrylic discs to stack up on top of one another. I added an alternative rotation of the inner star shape, shifting it back and forth as to create some sort of chess board pattern.

TODO: Picture of chess board pattern viewed from both the inside as well as the outside.

The tube was big enough to be able to add two batteries wired up in parallel, while most components are mounted on the underside of the pcb.

With the design becoming more and more finalised I did update the 3d model to reflect the current state of design:

TODO: Screenshot of higher sandwich lamp in two woods

TODO:

  • Pitfall: Charging the battery would switch on the light