The traditional clock shows time on a screen, two dimensional and depth-lacking; the traditional mirror reflects a person once, flat image and fun-lacking; the traditional music player plays music, but you can not see it. Yet we live in a physical world where the real-world objects are complex and three-dimensional, our ability to perceive and understand the world will be greatly enhanced were more depth dimension information included for all the traditional displays.
Our project product, the Infinity Mirror Music player, displays music spectrum in the air, infinitely. With the propeller clock feature, the real-time clock will be displayed on our 3D propeller screen; with the infinity optical effect, you get a magic mirror that creates mesmerizing effects with colored LED strip; with the music playing function, you see your music rhythm in the air. In this project, the Raspberry Pi 3 is used to control the system display, automate the system and transfer the mode from welcome mode to clock mode and then to music mode after powering on.
The Infinity Mirror Music Player is an eye-catching displayer that combines persistence of vision optical illusion and infinity mirror effect. As a clock, it is unique in that the system utilizes persistence of vision theory to display real-time clock with the illusion that the numbers are floating in the air, in a three dimensional way. As a mirror, it produces the illusion of hundreds of glowing clocks receding into infinite depths when observing from the top. As a music player, it decodes the real music into frequency domain magnitude and display it on the rotating screen.
The whole system can be divided into three main subsystems: the Propeller Clock Displayer, the Infinity Mirror, the Raspberry Pi3 Control Module.
Figure 1: the whole system design
The propeller clock module, the primary display screen of the system, is consisted of the following main hardware components: a 12V motor, which is attached under the base board and fixed by a motor holder to the base board, is utilized to rotate the proto board. Here the proto board is a PCB board that is used to hold the other major components, including the Adafruit Dotstar LED strip, the Arduino Pro mini, the Hall sensor, and the Bluetooth to UART module. As for these components on the protoboard, a Dotstar LED strip with 8 LEDs will be used to display the content while rotating. Arduino pro mini will be used to control the LED strip display and communicate with the Raspberry Pi3 to control the whole system. A wireless Bluetooth to UART converter will be used to transmit the control signal from Raspberry Pi 3 to Arduino. A hall sensor, which is fixed on the board, together with a magnet, which is fixed on the regular mirror surface, is used to detect the starting point and refresh the display screen. A DC motor control module is planned to be connected with the board and control the rotating speed of the board( which was removed in the end as it introduced unstability to the motor rotating speed). In this module, balancing of the propeller clock will be our major challenge.
The primary power supply of the propeller displayer module is achieved with the help of a 12V 600mA wireless charging module. Three main power supply techniques were tried out thoroughly (explained in the next part), we choose the inductive charging system due to its lightweight and space-saving features.
Figure 2: the propeller displayer
The infinity mirror adds a bonus mesmerizing visual effect for the whoe system. This module contains a special one-way mirror, a regular mirror, and a baseboard. All mirrors will be laser cut to be round-shaped. The special top mirror (the one-way mirror) is 50% reflective and 50% transmissive; the mirror in the middle (under the rotating board and on top of the 12V motor of the propeller clock) is a normal mirror that reflects the light. The normal mirror is used to reflect the LED screen display and will be installed in between the rotating board and the 12V motor. The displayed message will bounce back and forth between the two mirrors. With some lights escaping from the top mirror, the reflected displaying will become less and less each time. In this way, the gradually dimming illusion can be observed as hundreds of depths.
Figure 3: the infinity mirror
In order to control the display messages of the propeller displayer and achieve the automation of the whole system, Raspberry pi 3 is used to communicate with the propeller clock module. For the message design, the system will display three types of messages: some specified characters, real-time clock, and the music spectrum. For the automation part design, the system will displays a welcome message on the 3D screen and a welcome audio while powering on. Followed by a brief introduction of the system, it will then switch from power mode to clock mode when the rotating speed increases to stay stable. Then the music will be played and its spectrum will be displayed on the screen. The Bluetooth to UART converter on the rotating board serves as both the means of uploading programs from our computers to Arduino pro mini and the communication media between the two microcontrollers: the Arduino mini pro and the Raspberry Pi 3.
For the controlling programs on the Raspberry Pi 3, we first need a PWM control program with GUI to help test the motor rotating. Then we will develop a program named test_BT.py to test the communication of Raspberry pi3 with Arduino pro mini via Bluetooth. We plan to use socket for communication between raspberry pi and Arduino. In the end, a final control and music sdisplay program on the Rapberry Pi 3 will be
Figure 4: software design flow chart
The test and redesign steps for the major components of the system were conducted as follows:
The propeller displayer was the main display screen for the whole system. It utilizes persistence of vision theory to display the illusion of stable patterns floating in the air, thus it requires demanding rotation balance skills, which does not fall within our familiar expertise.
The protoboard system was even not balanced when we set up the initial system and began the rotation test. We first changed the Li-ion battery position as initially we put the battery on one side of the rotating board. As the battery is definitely the heaviest part on the board, we put it to the center hoping to improve. But as the battery module itself was not symmetric, we still cannot balance the system. We searched several solutions on Internet, and removed our power supply system for the propeller clock off-board (explained in power redesign module), then the board itself can be balanced.
Then the led strip was added, the rotating clock could not maintain balance again. One possible reason may be that the LED strip is too soft to keep in position when the motor was rotating at a high speed(around 1800 rpm). As for this factor, we thought of using structure wood to support the led strip. Another possible reason for the unbalance introduced by the led strip is that the LED strip was mounted only on one side, we need to add one similar structure to the other side to balance during rotating. In the end, we found a more stiff material to hold the LED strip and use four wires to hold the whole system, structured like a bridge. We also added some coins to balance the weight and adjust carefully the distance. Finally, the whole system was successfully balanced with all components.
The redesign of the charging system has gone through a Li-ion battery to a slip ring, then to inductive wireless charging module. At first, a rechargeable Li-ion battery will be used to charge the propeller clock module. Following our initial charging system design, we successfully recharge the Li-ion battery using the lab power supply equipment, and modified the Li-ion battery boost module, added a switch to control the power and added a charging circuit, in the end, we successfully have 5V output. But as the cumbersomeness of the battery made balancing rotating board so difficult, we removed it and tried slip ring to power the rotary part.
We made a slip ring to replace the Li-ion battery with the following steps:
The finished part picture is shown as below:
Figure 5: slip ring charging for propeller clock
The finished slip ring worked mostly OK except the motor became hot after some time when rotating. We suspect it’s mainly because of the insulation(the tape and glue) when fixing the slip ring on the motor. Also the slip ring will increase the resistance of the rotation part, thus the rotating board will become somewhat unstable.To combat this problem, we experimented inductive charging module to power the propeller displayer system, and tested the set with oscilloscope and assembled it on the system. This is a lightweight and stable solution that we finally choose to use for our project.
The Bluetooth to UART communication module is an essential part of the system communication and controlling. We initially used the module HC-06 to test the communication between the two microcontrollers, but we cannot get the desired reply from the serial to the Raspberry Pi monitor. To debug, we first checked all the hardware and made sure that the circuit is correctly connected. Then, we checked the connection between our computer Bluetooth connection and the module. The HC-06 module could connect to the computer correctly. We then did research on the internet and found similar bugs related to the HC-06 module, so we switched to HC-05 module instead. Using HC-05 module, the testing program could be uploaded successfully. We were also able to achieve the bi-directional communication between Raspberry Pi 3 and Arduino pro mini: the command could be sent to Arduino from Raspberry Pi 3; Raspberry Pi 3 could receive and display the reply information from Arduino.Finally, we redesigned the connector between the Bluetooth module and the Arduino pro mini to make it more compact and easier to balance on the rotating board.
Initially when Raspberry Pi 3 communicated the with Arduino pro mini, the reply from the Arduino was not correct. After some research we figured out that a time lapse need to be added between sending the command and receiving the reply. Otherwise, the reply will not be prepared, then the receiving buffer would not have the full reply. That’s the reason that the reply displayed on the screen was not correct.
At first, the character displaying effect on the propeller displayer is similar with the picture shown below(left): the shortest distance between the led light spot was separated around 4-5 centimeters. To improve the displaying effect, we reduced the delay time and finally delete the delay time between the two status(light on and off) entirely, but it didn’t work.
So, we suspected that the effect of the fastest updating rate may just be like this. We then searched the document of the dotstar led strip on internet and found that the updating rate could be super fast: for Arduino, the PWM rating could be 8MHZ, which is the clock rate. If that is true, we were supposed to get a better POV effect than the displayed effect. We then figured it might be the software problem. As we were using the Adafruit library previously, twe tried the Fastled library to see the display effect. It worked! The displaying effect with the new library is much better, shown in the picture below(middle).
With the new library, we could display the characters on screen better, but we want to display messages more precise and mimic the real-world display. So we tried to change the software SPI to hardware SPI by changing the connection within the system and got an even better display effect as shown in the picture below(right).
Figure 6: display optimization
Based on the third solution, we successfully displayed the character “ECE5725” on our system.
The main objectives outlined in the initial project plan were achieved successfully. We have finished the propeller displaying function, the infinity mirror displaying part, the music spectrum displaying module, control function. The few bumps happened mainly when we tried to balance the whole system, trying out the charging systems, displaying music spectrums.
The Propeller Displayer: the rotating propeller clock requires state-of-art soldering, delicate assembly of all the components on a small board, creative balancing ideas, numerous testing, failures, and improvements along the way.
The Infinity Mirror: The optical effects of the infinity mirror, combined with the propeller clock display, is a unique display system originated from creativity and passion.
The Raspberry Pi 3 Control Module: the Raspberry Pi3 control program is versatile in that it can be expanded to include more display modes by just including the corresponding display messages and switching functions.
Overall, this project allowed us to devote time exploring a cool project that we felt would be expanded to a real stunning product in real lives.
For the future work of this project, we planed the below functions: the system can receive music signals from mobile phone, a special equipment to control the display depth of the infinity mirror can be designed, so that more display effect choices can be set. We also want to add more interactive functions to this displayer like a touch screen or voice control. All in all, in the end we want our product to achieve touch screen, voice control and displaying depth control functions. We will continue to finish all these functions after this course.
In terms of the contributions, BeiTong focused on the hardware hacking, while Qian focused on the software testing and display program part initially. We tested different techniques for balancing the system together, and BeiTong built the music spectrum display program part. This brilliant idea was brought up by Beitong Tian, and he contributed a lot of his prior expertise and experience on Embedded Operating Systems.
|Motor 12V with Copper head||10||Amazon|
|Bluetooth to Uart Converter||7.5||Amazon|
|Inductive Charging Module||10||Amazon|
|Raspberry Pi 3||35||Provided in lab|
|Arduino pro mini||6.5||Provided in lab|
|Adafruit Dotstar LED strip||5||Amazon|
|Proto board||0||Provided in lab|
|Motor holder||0||3D printed in RPL|
|Infinity mirror Base||0||Recycled|