Utilising UVA LEDs in conjunction with Lumious paper and a single axis lead screw to creatre a dot matix clock

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This is a clock based project. The title of which embodies the main means of displaying the time.

The "Lumi", being an abbreviation for Luminous.

Utilising lumious paper in conjunction with UVA LED's to display the time which fades over a period of time between updates.

For a bit of added nostalgia, the numbers are in a dot matrix format.

In addition to luminous paper and UVA LED's the clock uses a Microbit, RTC, Digital Logic, 3D printing and Mechanical parts.

This project makes use of Photo Luminescence using paper layered with Strontium Aluminate which has a green glow although different mixes can result in different colours and persistence.

Once charged, light from the paper will continue to be emitted after the charging light has been remove. The charging light in this case comes from UVA LEDs.

The light emitted after charging is initially very bright but quickly decays to a lower intensity becoming further deminished over time, this persistance can last for several hours. if the paper is exposed multiple times in relatively quick succession then multiple ghost images will be present. Therefore, to minimise this effect a delay is applied between successive exposures.

Consequently, this project is best viewed in a low light environment.

UV LED's are used to illuminate luminous paper but require some means of moving the LED's over the paper to create the numbers.

This is achieved by using a single (x axis), leadscrew.

The leadscrew is directly driven by a DC motor which can rotate clockwise and anti-clockwise.

Fitted to the leadscrew is an arm and to this 8 LED's are attached to form one column.

Although 8 LED's are available to form characters, only 5 will be used at this time to retain compatibility with the Microbit display.

As the leadscrew rotates the arm moves across the paper pausing momentarily to turn on the required number of LED's this continues until all the required numbers are displayed.

The leadscrew supports the LED arm and is 3D printed.

Each character is stored as an array element in a string of five 2 character decimal numbers, one number per column

When converted to binary the character is formed in a 5 x 5 matrix

Each array element from 0 to 9 corresponds to the numbers 0 to 9

0 = "1417211714" ... 9 = "0221130502"

All elements are connected to the Robotics Board, this can control 4 motors and 8 servos and allows connection to MicroBit pins.

In this application only one motor will be used which will drive the leadscrew.

No servos will be used but instead these 8 outputs will be utilised to control 8 UV LED's

Hall sensors will be connected to the MicroBit on P1 and P2 for endstop detection. Both active low.

Buffer enable (active low), is on P8

Time setting is enabled and disabled with a switch connected to P0.

Button A is used to set the Hours and this is connected to an external switch connected to P5

Button B is used to set the Minutes and this is connected to an external switch connected to P11.

Some soldering is required for the IC buffer, Hall sensor circuits, pin headers on Microbit and LED board.

Short 100mm jumpers are used to connect the RTC and Micro USB breakout.

A combination of 185mm jumpers and custom leads are made for the longer cables runs to the Buffer Board, LED's, Hall sensors, switches and motor.

The Hall effect sensors are omnipolar, meaning they will respond to either magnetic polarity.

They are open collector output, meaning that a pull up resistor is required, in this case 2K2R.

The 100nF capacitor is for noise decoupling.

For ease of insertion or removal the sensor is screw fitted to a 3pin terminal block whilst the resistor, capacitor and flying leads are soldered to the pins.

When powered and in the abscence of a magnetic field the output is High when a magnetic field is detected the output goes Low.

Ensure that is sufficient cable length from the right hand motor support to the Robotics board.

The UV LED's are not driven directly by the microcontroller.

We will make use of the Robotics board which has 8 servo outputs allowing us to control each LED individually with PWM.

But due to low drive capability a buffer IC rated up to 7.8mA per output is used to drive the LED's from a 5V supply.

The IC is a Non Inverting Octal Buffer with TriState outputs. In this case the IC is mounted on a piece of stripboard in a IC socket.

Right angle pin headers are used to make the connections for inputs, outputs and power.

... Read more »


Lumiclock schematic

Portable Network Graphics (PNG) - 66.48 kB - 07/02/2022 at 18:16


  • 1 × Microcontroller Microbit
  • 1 × Real time clock DS3231
  • 2 × Resistor1 2k2
  • 2 × Resistor2 10k
  • 8 × Resistor3 220R

View all 21 components

  • 1
    Lead screw cap

    The leadscrew cap allows the tension on the bearing to be adjusted to reduce wobble.

    Apply, glue to the external surface of the 10mm long M4 hex standoff and insert into the leadscrew cap, allow the glue to cure.

  • 2
    Motor coupling

    Into the side hole in the motor coupling carefully insert the M4 x 6mm grub screw and tighten.

    A thread will be cut into the plastic as its tightened.

    To prevent stripping the thread or possibly splitting the plastic, tighten half a turn than slacked by a quarter turn until the grub screw is visible in the motor spindle hole.

    Apply, glue to the external surface of the 5mm long M4 hex standoff and insert into the motor coupling, allow the glue to cure.

  • 3
    Motor Support

    Solder the Shim to the back of the motor to enable connections, in this case the shim uses a JST-ZH and the other end is connected to DuPont pins to fit in the screw terminals on the Robotics board for the motor.

    The motor is a push fit into the motor support, although some filing may be required.

    In the event that it does not fit snugly, a cap is included to hold it in place.

    Once the motor is fitted the coupler can be attached as a push fit with additional security enabled by tightening the grub screw.

    Align the flat of the motor coupling with the flat on the spindle and fit the motor coupling over the motor spindle.

    There are four 3mm holes in the motor support .

    Attached to these holes are 20mm hex standoffs held in place with M3 x 12mm bolts.

    The rail support also with four 3mm holes is aligned to the hex standoffs and fixed with M3 x 12mm bolts.

View all 8 instructions

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