Smallest Handmade LED Screen

Here’s a video of the smallest screen I’ve made to date.

It measures 15mm squared and has a total of 64 LEDs.  Initially I had designed this circuit to use a (pretty expensive) LED driver chip because in the past the intensity of light was lacking.  It turns out that the tiny LEDs I used for this project are so bright that I didn’t need it.

It’s a hand soldered, hand etched circuit board and employs a technique that I’d been wanting to try for quite some time.  The display uses a technique called ‘Charlieplexing’ that employs columns and rows.  The thought of trying to come up with a layout to facilitate this on a hand etched board was very unappealing so what I did instead was to layout the columns on the board, solder the (surface mount) LEDs and then solder the rows on top of the LEDs.

It was fiddly work, done under the microscope, but it was definitely worth it!

Retro Clock

I’ve had this 7 segment display for as long as I can remember, but never did anything with it until now.  I wanted to learn how to interface with real time clock chips and so this was a perfect excuse to finally use it.

It’s only breadboarded at the moment; soon I’ll etch a custom board as well as fabricate a nice case for it.




The clock chip isn’t shown in this photo.  I’m using an Arduino Nano and a Charlieplexed interface to the display.


The display doesn’t ‘know’ how to represent characters such as ‘4’ or ‘8’ and so in my program I define the numeric and time seperator characters I need.

The clock chip benefits from a watch battery (what a surprise) to prevent it from losing the time when the main unit is unplugged.

Skate light revisited

A few years ago I put a pair of lights on my skateboard and took some 60 second exposures of the board in motion, as well as some nice hand held twirly light effects:



The problem though was always one of battery robustness.  The lights are 12V, and my solution then was to use a single 12v penlight battery- but for the life of me I could never find a battery holder for them.

So I made my own, but it was never as rugged as it could have been.

Fast forward a few years.  I learned to weld, and make things properly.  Enter the steel frame of doom!

Oh yeah, and the onboard Arduino!  Yes, it was time to put some smarts onboard.  The Arduino Uno is connected to a tilt switch than gives a pretty good idea of when the board is decelerating and so can turn on the rear ‘brake’ light when this happens.

Here’s the cover I’ve placed over the steel ‘room’:


Needless to say it’s also possible to fade up and down each light, adding to the overal laser sound effect aspect of all of this.

Here’s the ‘headlight’:

.. and the ‘Brake Light”:


Not only does it keep me safer out on the roads at night, it also makes real purty artworks.




 The ‘Thermomo-jacket’ is a simple wearable thermometer that represents the temperature inside the jacket as different hues of colour.  At around 10 degrees Celcius the LED lights blue. It’s nice and warm in my house, so I took a quick walk in the winter air before taking this photo. Brrrr!


Things are heating up- this is around 18 degrees. Temperature is mapped to hue. The saturation and brightness of the colour was kept at 100%.


In the mid 20’s the LED glows yellow then orange. This is a really warm jacket, so a fast temperature rise is inevitable. 


In the high 20’s the LED glows red, or even a little violet. Hot stuff… coming through!
The LED is very bright, and the three colours are produced by three separate LED’s, and so I’ll need to add some sort of diffusing material to cover it. Otherwise, a colour split occurs. In the picture above, the colour should be orange, but we see separate green and red colours. For the series of pictures above that, I used a small piece of masking tape. Obviously this won’t do for high fashion!
Here’s the LED itself- its pins have pushed through the jacket, and are wired up on the other side. It’s an RGB LED- which means that one can control the individual red, green, and blue lights.
The LED and the thermistor (a resistor that changes its resistance with temperature) are connected to the microcontroller board:
A: In the foreground is a power regulator, which provides nice, stable power to the microcontroller. B: This is the microcontroller. C: The brown pillowy thing in the background is the ceramic oscillator- it’s the component that provides a 16MHz timing signal to the microcontroller.
Here is how the thermistor was wired up:
The Arduino board has several analog inputs, that require a varying voltage. This voltage needs to change as a function of the resistance of the thermistor. The best way I know to achieve this is with a voltage divider:
As the resistance of the thermistor changes, so does the voltage ‘XV’. This value is read by the Arduino board, and then in software I map this to colour. The thermistor is hidden near the LED, next to the wool of the jacket, and so it tends to get very warm very quickly.
Here’s another detail of the wiring to the thermistor:
The blue wire gives the variable voltage level. Notice how everything is heat-shrunk. This ensures no short circuits can occur as the thermistor moves around inside the jacket.
For the future: I plan to add a second thermistor, on the outside of the jacket. Then I can measure the difference between the inside and outside temperatures, and represent that via the LED.



LASER scanner

I recently converted my home-made Meccano 2-axis webcam mount into a laser mount. The system is made of an Arduino board that sends timed signals to two servo motors, mounted at right angles to each other. This gives a crude x&y pointer, which I can use to 'draw' patterns on any surface. My desk is illuminated by many vertical sweeps of a 1mW red laser. A Leica C-LUX1 was used in 60 second extended exposure mode.

This one is a visualisation of 'Brownian motion'. Brownian motion is analogous to a 'random walk'. The walk is not truly random because the same pattern will be generated every time the system is reset.



This image is a visualisation of the morphology of the 2-axis mount for the laser. It's clear from this image that the unit is more stable when making vertical sweeps than when it makes horizontal sweeps. The increment I used for moving the laser also affects the quality of the scan.



Now I'm telling the laser to point along 8 different directions. The unsteadiness mentioned in the previous image is seen along any direction that has a horizontal component. The increment used in this picture is small, so overall the quality of the line is smoother.



My desk is illuminated by an expanding 8 sided spiral. The laser gives a clue as to the type of material it hits,for example the translucent plastic of my computer versus the opaque wood of my desk.




In a future post: I've added a microcontroller switch to the laser, enabling me to 'pick up the pen' as it were.  Super-sneaky sneak preview: Here's a random dot pattern, playing across one of my clay sculptures: