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Mini Projects #002 – by Tim Blythman SILICON CHIP Lava Lamp Display Lava lamps have always invoked a fascination due to the seemingly infinite patterns that they produce. The Lava Lamp Display is a simple Arduino project that emulates a lava lamp, creating a soothing view that doubles as a groovy night light. T he lava lamp was invented in 1963 and consists of a glass bulb containing a mixture of liquids like oil and water. An incandescent bulb in the base heats the contents, and the different components swirl around due to their changing densities and surface tensions. The liquids are often coloured and the random, slow movements of their contents can be captivating and hypnotic. And bizarre as it may sound, lava lamps are even used as a source of random numbers for encryption. Companies like Cloudflare use them as part of their encryption process (see https://youtu.be/1cUUfMeOijg). Our Lava Lamp Display is a simulation of a lava lamp, using software to imitate the physics. We can’t simulate things down to the atomic level with an 8-bit processor, but we can create something that looks and behaves similarly. Our Display isn’t actually random, but it looks like it is. The photos shows how the completed Lava Lamp Display uses an 8×5 LED matrix shield mounted on an Arduino Uno board to provide the processing power. Simulation The simulation involves several ‘blobs’. Each has a ‘temperature’ and position within the display. They are analogous to the balls of oil that break off and travel around a Lava Lamp. The temperature determines whether or not the blob rises or falls, mimicking its density changing. The position affects the temperature; when the blob is near the bottom, the temperature increases, as though the blob is being heated. Near the top, the temperature falls, as though by radiating heat to the surroundings. This feedback sets the scene for the constantly changing movement of the blobs. To avoid the blobs overlapping and disappearing, the simulation prevents a blob from moving on top of another. Assembly of the Lava Lamp Display just involves plugging the LED matrix shield into an Arduino Uno (shown above). The blobs in the Lamp drift around like those in a lava lamp. The software can be modified to alter the colour or behaviour if desired. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au Lava lamps are produced in a variety of colours, and they produce unique and constantly changing patterns. Source: https://w.wiki/9TUn (CCA 2.0). To prevent a deadlock, blocked blobs occasionally move in a random direction. This randomness comes from a pseudo-random number generator. The blobs’ colours also change depending on their temperature, adding further variety to the display. The result is a fairly convincing simulation of a lava lamp. Hardware and assembly The construction phase of this project simply involves plugging the XC3730 shield into an Arduino Uno board. The XC3730 LED Matrix Shield uses so-called ‘intelligent’ RGB LEDs. We described how these LEDs work in an article on page 85 of the January 2020 issue of Silicon Chip magazine (siliconchip.au/Article/12228). In summary, we can drive all 40 RGB LEDs on the shield using just one digital output on the Uno. Since the LEDs are already attached to the shield, assembly is simple: plug the XC3730 LED Matrix Shield into the Uno and connect the USB cable between the Uno and a computer. Programming the Arduino You will need to install the Arduino IDE software plus some custom libraries. Adafruit’s NeoMatrix library is responsible for driving the display. It can be installed (along with its other dependent libraries) by searching for “neomatrix” in the Library Manager – look for the version by Adafruit. siliconchip.com.au Download and unzip the software package for this project, which is available from siliconchip.au/Shop/6/396 Next, open the XC3730_LAVA_ LAMP_COLOURS sketch, select the correct board type and serial port from the menus, then upload it to the Uno. Arduino boards like the Leonardo should also work, but we haven’t tested that. If all is well, you should see a display similar to that seen in our photo. There isn’t much that can go wrong; it should just work. A video of it can also be found at siliconchip.au/link/abu8 Software details The software has been written to be configurable, so there are some #defines and variables that you can change to customise your Lava Lamp Display. Remember to upload your sketch again after any changes so that they can take effect. The BACK_COLOUR #define sets the background colour; the default is a dim blue. Changing the number in the line matrix.setBrightness(6) will alter the display intensity. We have set it quite low so that the Lava Lamp Display is suitable as a night light or for nighttime mood lighting. The colour of the blobs is set by the tempColour[] array, based on the blobs’ temperatures. The default is quite subtle; you can try uncommenting one line at a time to see different schemes we have tried, or you can make your own. To speed up or slow down the Display, you can change the delay() function call within the loop() function. A higher value will result in a slower update rate. You can also change the number of blobs with the BLOB_ COUNT #define. The heatMap[] array dictates how the temperature changes based on position. The updateBlob() function encapsulates the physics of how each blob behaves based on its temperature. For more advanced constructors, modifying the code can produce some significant changes to the simulation. All of these changes will have very subtly different effects on the model’s behaviour and lead to so-called emergent behaviour, where a simple set of rules can result in complex outcomes. Another example of emergent behaviour is a set of mathematical rules called Conway’s Game of Life. You can see examples of this at https://w.wiki/3TKJ We have also written an implementation of this scheme in a sketch called XC3730_CONWAY, which you can try out by uploading it to the Lava Lamp Display hardware. It is included in the same download package. There is an array you can use to set the initial conditions, after which you can see how the state evolves. Each LED is either lit or not; its state in the next phase of the sequence depends only on it and its immediate neighbours. The rules are pretty simple, but the animations generated almost look like they are alive, hence the name. Conclusion The Lava Lamp Display takes a simple simulation of lava lamp physics and turns it into a unique and mesmerising display that can be used as a night light or simply for amusement. It shows how simple rules can combine SC to create complex behaviour. Parts List – Lava Lamp Display (JMP002) 1 Arduino Uno microcontroller module [Jaycar XC4410] 1 8×5 RGB LED Matrix Shield [Jaycar XC3730] 1 USB-A to USB-B cable [Jaycar WC7705 or similar] Australia's electronics magazine July 2024  65