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Fun projects for the Raspberry Pi Model A+ – Part 1

Fun Projects for the Raspberry Pi Model A+ – Part 1

The latest release of the Raspberry Pi, the RBPi Model A+ is not only smaller, it is cheaper as well. That makes it an ideal device for taking a plunge into coding and for trying out new projects. Here are some fun projects that you may find interesting.

A Garden with Digits

With a Pibrella add-on board, your RBPi can run several small motors to create a digital garden. Define the garden to your exact specifications with ornate flowers that you could make out of card or cloth. Add artificial bees and make then spin when you press a button. You could also arrange a relaxing setup of plants and have some soothing music going on at the same time. For details, look here.

Juggle With Illuminated Pins

This is for those who like to juggle things. While juggling, let your RBPi help you out with the routing using some extra LED lights. You will need a Pibrella board and some custom Python code to make the project work independently. Although this may be a niche case, the project is worth undertaking. Lauren Egts has a blog post.

Console for Retro Games

Arcade cabinets of yesteryears still draw a lot of interest. Both young and old enjoy retro games and your RBPi can work as the basis for such a console. With RetroPie, you can simply load emulator software. All you need is an SD card and some USB peripherals. This simple but fun project can be completed within one hour. Life hacker has a guide.

Control Your Pottery Kiln via Wi-Fi

Those using kilns for firing up potteries will find this project useful. RBPi provides remote capabilities for automatic temperature control using a thermocouple and a stepper motor. Temperature stability is maintained with a system of closed-loop feedback. Visit the RBPi blog for code and photos.

Watch Birds with Infrared

Although this is a project for birdwatchers, others can adapt it for their own requirements. An RBPi makes it possible to watch what birds are doing inside the bird box. This way, you are in complete control of watching birds on the outside as well as on the inside of the bird box. The RBPi even makes it possible to set up a live internet stream if your bird box is in a remote location. You will need the RBPi NoIR camera board and some infrared LEDs. The RBPi site has more details.

RBPi Weather Station

You do not need to rely on forecasts from the radio or television any more. Make your own weather station with the RBPi. This project is very cheap and requires very little energy. Of course, some extra hardware is necessary, but nothing too complicated. For details on the setup, visit DragonTail.

Transmit Morse code

Although this is ancient technology, people dabbling in Amateur Radio still find Morse code very useful. Building an RBPi powered Morse code station will be a very exciting project. With this, you can have device for encoding and decoding Morse code. If you add a vintage Morse key, the authenticity of the project will increase dramatically. For complete details, head over to the RBPi website.

Telegram, Raspberry Pi and Remote Control

People from an older generation may still recall the days the postman would land on the doorstep and deliver a slip of paper with some message in it. Those were the days of Telegrams associated with Morse Code, the dots and dashes way of communicating with far-off places. Mobiles and instant messaging services have now replaced that and other such slow modes of communication. As a result, you can always remain in instant contact with people across the globe.

Similar to the WhatsApp messenger service, Telegram is another application that allows you to chat and share documents with your contacts. Telegram surfaced when WhatsApp crashed about a year back. Being a cross-platform messenger app from Berlin, it gained above five million users within 24 hours and more, since Facebook purchased WhatsApp.

Although at first introduction Telegram and WhatsApp seem identical, there are interesting differences. Both require the telephone number of the recipient for sending them a message. In addition, chatting to individual contacts or to groups is possible. Both have a single and double track system for knowing if the recipient has received your message and has read it.

However, unlike WhatsApp, Telegram allows you to send your messages, videos and photos with a self-destruct timer. Once the set time ends, all your shared documents disappear within a ‘secret chat’. This has a huge advantage. Under secret chat, all documents, locations, videos and images remain encrypted end-to-end and only the sender and the recipient can read them; nobody else can read them, not even the staff at Telegram. The timer can be programmed to activate either after two seconds or up to a week.

Using Telegram on the RBPi is fun and you can use the versatile instant messaging service on the same phone number with different devices simultaneously. Apart from simply using the messaging service to exchange messages, it is also possible to make the RBPi take specific actions automatically, based on the message received by it. For example, if the text message sent is say, “photo”, the RBPi responds by taking a snap of the surroundings with its camera and sends the image to the sender. Similarly, if the message says “lamp”, RBPi can turn on a lamp or open a garage door if the message says “open”.

For using Telegram for remote control, it is best to use the RBPi model B or B+ and have the latest version of the Raspbian as the operating system. However, you can also use the pre-installed Raspbian on the 8GB Class 10 Micro SD card available here. Follow the configuration given in this tutorial as a starting point.

RBPi will be intercepting new incoming messages with Lua, a lightweight, fast, powerful and embeddable scripting language application. Lua uses extensible semantics and associative arrays by combining the simple procedural syntax to powerful data description constructs. That means Lua has the capability to understand text and interpret the action to be taken. In fact, Lua uses a lookup file “action.lua”, much as we use a dictionary, to correlate specific text messages received and the actions that RBPi will take. For details of programming, refer to this blog.

What is a dual screen smartphone?

Most of us use smartphones that sport dual features such as two cameras, two flashes and two SIM sockets. Some manufacturers also make phones with two glass layers for encasing the device. However, one manufacturer has literally followed the adage – two heads are better than one – and produced a smartphone with two screens.

The world’s first dual screen phone – YotaPhone 2 – Is a product of the Russian company, YotaPhone. While the primary display measures 5.0 inches and is an AMOLED display of 1080x1920p resolution and a pixel density of 441ppi, there is a second display on the rear panel. This has a dimension of 4.7 inches, a resolution of 960x540p, a pixel density of 235ppi and is an e-ink display.

The e-ink, rear panel display of YotaPhone 2 has a back matte finish that makes it easy to read from the black and white display. Both, the primary front AMOLED display and the secondary rear e-ink display are protected with a highly resilient layer of Corning Gorilla Glass 3.

Since the secondary display is fully touch-sensitive, you can personalize it easily. For example, rig it up to display notifications and it will show all information of your choice. The main advantage of having a secondary display is power savings. Waking up the full-color display just to check on notifications about messages and mails requires a lot of power. Using the secondary display consumes only a fraction of the power required by the main display.

While on the high-resolution front display you can play games and watch movies, the monochrome rear display is more suitable for static functions such as reading e-books. It is easy to operate one screen at a time, since you can lock out the other one. Operating with the monochrome display saves considerable battery power. However, there is one disadvantage with the monochrome display. An imprint of the previous image can still linger on when you have changed to a new one.

The driver behind the YotaPhone 2 is a Qualcomm Snapdragon 800 SoC. This runs on a 2.3GHz quad core Krait 400 CPU and an Adreno 330 GPU. A healthy RAM storage of 2GB is supplemented with a phone memory of 32GB. YotaPhone 2 comes with an 8MP rear camera and a 2MP front-facing camera. Out of the box, the phone runs Android 4.4 and to accommodate the secondary screen functions, YotaPhone provides the necessary firmware tweaks.

A non-removable, 2500mAH battery powers the device. The phone is capable of being wirelessly charged. YotaPhone has, by design, not provided a very large battery as the secondary screen provides power saving benefits. Additionally, the lighter weight of the battery offsets the increase in the weight of the phone because of the presence of two screens. Additional weight would have made the phone inconvenient to carry. As such, the presence of two displays has significantly increased the thickness of the device.

YotaPhone 2 is fitted with a glass fiber body. This is solid enough considering the weight of the phone at 140gms and a thickness of 8.9mm. The soft curvy edges deserve applause.

What is a Broadband Internet Connection?

To access the internet from homes, offices or mobile devices, internet services are necessary. This is offered in mainly four different forms – Digital Subscriber Line or DSL, cable, fiber-optic and satellite. All the above are commonly known as broadband services since they provide high access speeds compared to the old dial-up connection, which is the only non-broadband service. Although this is the cheapest way of connecting to the Internet, most users prefer faster connections such as provided by a broadband Internet connection.

The DSL connection makes use of unutilized telephone wires to provide Internet service. The speed of the connection varies with the distance of the user from the switching station – the speed will be slower the further away the user is.

A local provider of cable TV provides broadband Internet services through cable. Here, there will be several subscribers on a single service, sharing the bandwidth. The speed will vary with the number of users on the service at any specific time – decreasing as the number of connected users goes up. The speed is usually at its lowest at peak times, for example in the late evenings when many people will access the internet after the day’s work is over.

Fiber optics provides the fastest Internet connection and is the latest method. Since it is one of the newest methods, service areas are limited. In addition, laying fiber-optic cables under the ground is a time-taking task. Although the cost is comparable to that of both DSL and cable, the service provided by the fiber-cable is of a much faster connection.

Satellite services are one of the slowest forms of Internet connection and the most expensive. They are also notoriously complicated to set up and use. However, for people living in remote rural areas, a satellite broadband Internet service may be the only means of communication possible.

Broadband Internet services provide several advantages over more conventional means of accessing the Internet. DSL and cable connections are very easy to obtain and connect with the computer. The high speeds enable users to multitask while working on the Internet. For example, it is possible to surf the net while listening to music over the web.

At home as well as in the office, networking of several computers is made easier with a shared broadband connection. Both wireless as well as wired modems are available for this purpose.

Another trend recently introduced is the mobile broadband service. The modem offered is typically in the shape of a USB stick, only larger. It comprises a wireless device and a socket for the SIM card. When connected to the computer and supplied with the username and password, the wireless device searches for and connects to the transmissions of the service provider. Nowadays, with newer devices in the 4G or fourth generation, very high speeds are achievable.

One of the main advantages of broadband services is that it will not keep your phone lines engaged while you are surfing. This was the case with the old dial-up type of Internet service, where the user would not be able to make or receive telephone calls while connected to the Internet.

How does fiber-optic broadband work?

Fiber-optic broadband is a high-speed form of connecting to the Internet and works by sending and receiving signals over an optical fiber cable. Unlike the majority of broadband connections in the world that use mobile networks or the telephone lines, fiber-optic broadband transfers signals via special cables under the ground. These signals use light and optical fiber as against copper cables and move a lot faster offering speeds as high as 1Gbps.

Laying optical fibers under the ground is an expensive and time-consuming process. If you are in an area that is served by optical fibers, you can sign up for this superfast fiber-optic broadband service. Even the cheapest fiber-optic connection will provide speeds well in excess of any standard ADSL broadband service. Cheaper services often combine fiber along with copper wires to deliver the connection to your doorstep and are known as FTTC or fiber to the cabinet broadband. This type of connection usually has the fiber-optic line running from the provider to the junction box just outside your house. From here, normal copper wires carry the signal inside your home.

A better type is the FTTH or fiber to the home connection. This will have the fiber-optic cable run all the way inside your home. FTTH is better as it provides speeds up to 300Mbps as compared with speeds of about 75Mbps for the fiber to the cabinet service. However, FTTH services are not so widely available yet.

What can you do if you have a high-speed Internet connection? For example, with only a 50Mbps connection, you could download a 10GB Blue Ray movie in just under a half-hour or download an album of the size of 100MB within 15 seconds. FTTH provides several additional options such as to receive cable TV, phone lines and other excellent bundles with packages offered by service providers. The extremely high speeds offered by fiber optics has made it the backbone for much of the Internet deployed. In the US, the latest deployments are from Google Fiber and Verizon FiOS.

Fiber optics provides several benefits such as faster speeds over much longer distances as compared to the traditional copper-based technologies such as DSL and cable. Although the actual service you get depends on the company providing the service, but in most cases fiber will give you the best bang for the buck. In addition, fiber optics is future-proof as well. Even if broadband speeds increase by 1000 times in the near future, the existing single fiber-optic connection will easily support it.

Technically, fiber optics uses light in place of electricity for transmitting data. That means, much higher frequencies are used and the data capacity is enormous. The fiber-optic cable itself is made of glass or plastic and therefore, immune to electromagnetic interferences unlike metal cables are. Therefore, more data can be transferred to greater distances without any degradation.

Energy loss and interference are the limiting factors for most type of communication transmission, but fiber optics handles these factors in a much better way than any other modes of transmission. However, the biggest limiting factor that is currently hindering the widespread adoption of fiber optics for Internet access is the cost requirements of replacing DSL and cable networks.

Balance your robot with a Raspberry Pi

You may have seen the amazing two-wheel scooter, the Segway Human Transport system. It has only two wheels, a platform for a person to stand and a handle to guide the vehicle. The scooter operates on batteries located under the platform and between the wheels. Dean Kamen is the inventor of this amazing transporter, which can carry a person around while balancing on its two wheels without toppling over.

After watching the amazing Segway scooter, Mark Williams tried his hand at balancing a two-wheeled robot using the tiny credit card single board computer, the Raspberry Pi or RBPi. You can watch his success in the video clip here – it is almost like watching a human baby learn to take its first tottering steps.

Mark’s PiBBOT, or Pi Balancing roBOT, carries its own power source and the electronics, but unlike the Segway, does not have room for a passenger. The TFT displays the angles from the accelerometer, the gyro, the complimentary filter and the power drawn by the motors. There are two buttons on the top – one for turning on/off the motors and the other for resetting the gyro.

The PiBBOT uses the concept of an inverted pendulum to work. This is similar to how children balance a vertical stick on a finger on their outstretched hand – they move in the direction the stick is about to fall, thus attempting to keep its center of gravity below it. The balancing robot keeps itself vertical by using a control algorithm called PID or Proportional Integral Derivative. It does this by trying to keep the wheels under its center of gravity. Therefore, if the robot leans forward, the wheels carry the robot forward, trying to correct the lean. As the bottom of the robot moves forward, inertia keeps its top in the same place, thus righting it.

PiBBOT has an accelerator and a gyroscope to measure the angle of its lean. One axis of the accelerometer measures the current angle, while one axis of the gyroscope measures the rate of rotation. A well-timed software loop running in the RBPi keeps track of both. The RBPi makes calculations based on the measurements to provide power to the motors via the PWM. The RBPi must move the motors in the right direction to keep the robot upright.

Accurate angle measurements need readings from both the accelerometer and the gyro, which are then combined. Individual readings do not provide the necessary accuracy. The gyro measures the rate of rotation and requires to be tracked over time for calculating the current angle. The tracking usually includes noise, which causes the gyro to drift. However, gyros are useful for measuring quick changes in movement.

Unlike a gyro, accelerometers do not need tracking and they can sense both static positions as well as sudden movements – with gravity defining the static position of the robot. However, accelerometers are notorious for their noise levels. Both gyro and accelerometers perform well over certain sensitivity levels.

Mark is using a measurement range of 250dps with a sensitivity of 0.0875 dps/LSB for his gyro. For his accelerometer, he is using 8g full-scale, corresponding to 4mg/LSB and a full scale of 10. Read the full details here.

How Are Sensor Hubs Helping Android?

The duties of a sensor hub are rather specific. They usually take the form of an additional micro-controller unit, a coprocessor or a DSP that integrates data from various sensors and processes them for the benefit of the main central processor. Not only does this technology off-load several jobs from the main central processing unit of a product, it saves battery consumption and provides an upward jump in its performance.

Most smartphone, tablet and wearable manufacturers including application developers are targeting mobile devices in the near future that will always be aware of their surroundings and activities. This will lead to providing meaningful results and content to the user. Inputs for the Always-on Context Awareness will be delivered by numerous sensors located within a mobile device, a separate micro-controller or a sensor hub fusing and computing their data.

PNI Sensor Corp. is making such a tiny 2×2 millimeter package as a sensor hub. It is by far the smallest, smartest and the lowest power-consuming implementation of a sensor hub. Consuming barely 200µA, this sensor hub implements the complete sensors function for the latest KitKat Version 4.4, as mandated by Google. Furthermore, PNI has incorporated all the KitKat functions without implementing an extra processor. This will greatly extend the battery lives of Android devices, even if they are using all their functions 24×7.

Android device manufacturers have two other choices. They could write their own fusion software and have them run on processors such as from Atmel or ARM. They could even license such software from others. On the other hand, OEMs could use smart sensors that have some functions implemented on-chip, while running the rest on the application processor. However, both the above methods are power-hungry and likely to consume up to ten times the power compared to the solution offered by PNI.

SENtral-K hub (the K standing for Google’s KitKat), from PNI can handle all the hardware connections from the MEMS sensors, while managing the virtual sensor functions in the software including the dedicated state-machine logic. The hub uses a tiny processor, the Synopsys ARC, along with specialized state-machines. Together, they achieve 140-thousand FLOPS or floating-point operations every second, while consuming less than 200µA at 1.8V. Being sensor agnostic, SENtral-K allows OEMs to select the lowest power consuming sensors from all different suppliers. This includes sensors such as for ambient light, pressure, proximity, magnetometer, gyroscope, accelerometers and many more.

SENtral-K combines all the outputs from the raw sensors and provides KitKat with the necessary functions it demands. These include functions such as step-detect, step-count, significant motion, linear acceleration including all the functions based on location and others that Google wants to incorporate at all times for their apps such as Google Now. The tiny chip comes fully pre-programmed to handle all functions demanded by Google’s KitKat 4.4.

For example, SENtral-K is capable of handling Android 4.4 KitKat functions such as those with nine degrees of freedom or DOF – 3-axis magnetometer, 3-axis gyro and 3-axis accelerometer. It can also handle six DOF – accelerometer and gyro or accelerometer and magnetometer. Other functions it can handle include Timestamp, Data Batching, Uncalibrated Sensor, Calibrated sensor, Significant Motion, Step Detect/Count, Linear Acceleration and Gravity.

Is there anything better than OLEDs?

Almost everyone uses a smartphone today and the displays are getting ever bigger. Larger screens are a pleasure to watch, but difficult to put inside a pocket. Therefore, Qibing Pei, a professor of materials science, is researching highly flexible and stretchable OLED displays that could allow a small elastic OLED smartphone to fit easily into one’s pocket and the screen could be expanded when viewing. That would certainly be a great help if successful, but in the meantime, there is something else, which is better than an OLED.

OLEDs require power and are expensive. Instead, carbon nanotube field emitters powering up a lighting panel are less expensive. They stimulate a phosphor in the panel to glow, much as the cathode ray tubes of the yesteryears did. The phosphor is brighter than the current OLEDs, consumes much less power compared to LEDs and is far less expensive than both of them are. Professor Norihiro Shimoi, a lead researcher at the Tohoku University in Japan is working on this technology. He uses light through a neutral density filter to illuminate nanotube field emitters to stimulate the phosphor.

Although the prototype in Professor Shimoi’s lab has yet to achieve 60-lumens per watt, it is similar in design to the flat version of the old cathode ray tube. Not expected for a commercial release before 2019, the nanotube prototype is like a lighting lamp, but with a power consumption of 1/100th of standard LED devices.

LEDs are all the rage today, owing their advantages over fluorescent and incandescent lighting because of the very low power consumption of LED based devices. With large-scale lighting, however, several LEDs have to be used together, which complicates the engineering and thermal design. On the other hand, the nanotube design is flexible enough to be formed into flat panels of any size.

Incandescent bulbs are the least efficient at a mere 15lumens per watt. In comparison, LEDs and fluorescent bulbs both produce about 100 lumens per watt. The difference is LEDs are point sources of light, whereas fluorescent bulbs spread their light over a much larger area. Organic cousins of LEDs, the OLEDs, produce about 40 lumens per watt but have the advantage of being incorporated into panels. According to Shimoi, simulating large phosphor-covered panels with electron field emitters made of carbon nanotubes will be more efficient. With their much lower power requirements, and producing 60 lumens per watt, these phosphors will potentially be brighter than OLEDs that produce only 40 lumens per watt.

Shimoi is currently working on reducing the energy loss by heat. The device employs highly crystallized carbon nanotubes and phosphors. These are coated with ITO particles. Shimoi is attempting to increase the electrical conductivity to reduce energy loss by heat. The process involves optimization of the crystallization of the carbon nanotubes along with the design of the lighting device.

Where typically, carbon nanotubes are made using semiconductor diode junctions, Shimoi has made them into excellent field emitters of electrons so that they can stimulate phosphors. Furthermore, production of these nanotubes does not require expensive clean rooms or high-temperature ovens. The nanotubes are single-walled and are grown by arcing.

What is BIOS – and will UEFI replace it?

BIOS or the Basic Input Output System, designed by IBM for its Personal Computers has been with us for more than thirty years now. Whenever a computer is switched on, it conducts a self-check to see if it has a keyboard, a display and memories. Then it proceeds to look for a suitable Operating System. A small program, the BIOS, resident on a flash memory on the motherboard accomplishes all the above tasks. Once it has found a satisfactory operating system, it hands over the control of the computer. Those who are into programming of micro-controllers will recognize BIOS as the Monitor program.

However, the humble PC has come a long way in these thirty years. From a paltry 4/8 bit system with hardly 256bytes of RAM, PCs now work typically at 64 bits and 8/16GBytes of RAM. The evolution of Operating Systems and external threats to PCs has led to a demand for an overhauling of the BIOS. Introduction of Intel’s Itanium processors in 1998 put the final nail in the coffin of BIOS and a new Intel Boot Initiative was born. This initiative went on to become the EFI, or the Extensible Firmware Interface. In 2005, a new forum was born, UEFI, a consortium of AMD, IBM, Apple, Microsoft, Intel, and so on.

UEFI, or the Unified Extensible Firmware Interface, is a complete re-imaging of the computer’s boot environment and has almost no similarities to the BIOS that it replaces. While BIOS is basically a solid piece of firmware, UEFI is more or a programmable software interface that sits on top of the BIOS. This BIOS is shorn off most of its boot code, and the UEFI handles that while sitting in a part of the non-volatile memory, either on the motherboard, on the hard drive or possibly on a network share.

In essence, UEFI resembles more of a lightweight operating system. When switched on, the computer boots into UEFI, carries out a set of arbitrary actions and then triggers the loading of an operating system. As part of its specifications, the UEFI defines the boot and runtime services, device drivers, protocols for communication between services and extensions. There is even an EFI shell that allows execution of EFI applications.

As UEFI is a pseudo-operating system, it is able to access all the hardware on the computer, allowing you to surf the internet from the UEFI interface or backup you hard drive. There is even a full, mouse-driven GUI. With the boot data now stored on NAND flash or on a hard drive, a lot more space is available for language localization, boot-time diagnostics and various utilities.

UEFI enables secure boot in that it can sense if a malware is trying to take over your computer even before it has had a chance to boot into its OS. This no-compromise approach to security offers unparalleled capabilities to the customers while at the same time offering full and complete control over the PC. UEFI can validate firmware images before allowing them to execute, based on the PKI process. This secure boot helps to reduce the risk of boot loader attacks.

Battle the Sun with a 21W LED and a Raspberry Pi

Lighting up an LED or an array of LEDs and controlling their brightness is a simple affair with the tiny credit card sized single board computer popularly known as the Raspberry Pi or the RBPi. The RBPi runs a full version of Linux and you can use it to drive an array of bright LEDs with it. If you construct it like Jeremy Blum did – he put up the LEDs on his graduation mortar board and wore the RBPi on his wrist on his graduation day – you can be sure of getting a lot of excited remarks from friends and onlookers.

Jeremy wanted to let others interact with the LED on his cap. Therefore, he developed the idea of “Control my Cap” project. His control system consists or a wrist computer comprising an RBPi together with an LCD/button interface. That allows Jeremy to monitor the status of the cap, adjust the brightness of the LEDs, change the operation mode and toggle the wrist backlight. If there is any trouble in connecting with the LED interface, the reasons will be listed on the LCD.

The RBPi is programmed to connect automatically to a list of pre-allowed WPA-protected Wi-Fi hotspots as soon as it is booted. This allows Jeremy to set the wrist interface and the LEDs to a web-controlled mode, let the LEDs take on a static color or have them follow a rainbow color pattern. The cap has a total of 16 LEDs, rated at 350mA each, with four each of Red, Green, Blue and White in four strings. A constant current driver that has a PWM control drives each string of LEDs. A separate on-board switching controller generates the 5V for the RBPi.

As the whole project is portable, a battery powers it. Jeremy used a laptop backup rechargeable battery for his project. At full brightness, the array of LEDs consumes a total power of 21W and is easily visible is bright sunlight. With an 87 Watt-hr. capacity, the battery is able to power the cap for an entire day and more. Additionally, it has a 5V USB port, which Jeremy uses for charging his phone.

Jeremy put up a mobile website controlmycap.com to allow anyone to submit colors for the color queue of the cap to be used in the web-controlled mode. In this mode, the wrist computer grabs the 10 most recently submitted colors from the mobile site constantly, displaying them on the cap. Additionally, when using a color set for the first time, the RBPi informs the requester by a tweet that their color combination is about to be displayed. The RBPi communicates with the cap via a single USB cable, which doubles as it power supply cable as well.

Jeremy used the FoxFi app on his Samsung Galaxy S4 smartphone to generate a Wi-Fi hotspot and the RBPi was able to connect to the Internet through this. The remote webserver hosting the controlmycap.com website also stores the color requests in an MYSQL database, which the RBPi queries for updating its commands.