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Hi! :)I am an Electrical Engineering student from Croatia and I built this device as a part of one course at University last semester. It is a fidget spinner which uses Persistence of Vision effect which is an optical illusion whereby multiple discrete images blend into a single image in the human mind.The text or graphics can be changed via Bluetooth Low Energy link by using a PC application that I have programmed in LabVIEW or by using a freely available smartphone BLE app.One of the most important characteristics is that the displayed graphics doesn’t depend on rotation velocity thanks to its innovative solution for keeping the track of rotation angle. Meaning that the displayed graphic is perceived the same at both, higher and lower rotational speeds (for instance, when the fidget spinner is slowing down when held in the hand).This is also one of the main difference between various POV device on the market (POV clocks, etc.) which must have a constant rotational speed in order for the image to be displayed correctly.It is also worth noting that all the components are selected to have the lowest possible energy use in an effort to prolong the battery life Technical DescriptionIt uses enhanced Microchip PIC 16F1619 microcontroller as its core. The MCU has built-in Angular Timer peripheral which uses omnipolar Hall sensor DRV5033 and one magnet to keep the track of current rotational angle.The graphics is displayed using a total of 32 LEDs, 16 green and 16 red light emitting diodes (nominal current 2mA). The diodes are driven by two 16 channel constant current shift register drivers TLC59282 connected in daisy chain.In order to have a remote access to the device, there is a Bluetooth Low Energy module RN4871 which communicates to the microcontroller via UART interface. The device can be accessed from either a personal computer or a smartphone.The device is turned on by using a capacitive touch button which is embedded under the solder mask on the printed circuit board. The output from the capacitive IC PCF8883 is fed to the OR logic gate BU4S71G2. The other input to the OR gates is a signal from the MCU. The output from OR gates is connected to the Enable pin of a step-down converter TPS62745. By using this setup I am able to power on/off the device by using only one touch button.Capacitive button can also be used to change between different modes of operation or for instance to turn on the bluetooth radio only when needed in order to save energy.Step down converter TPS62745 converts 6V nominal from the batteries to a stable 3.3V. I have choose this converter because it has high efficiency with light loads, low quiescent current, operates with a tiny 4.7uH coil, it has integrated input voltage switch which I use to measure battery's capacity with minimal current consumption and the output voltage is user-selectable by four inputs rather than feedback resistors (reduces BOM). The device goes to sleep automatically after 5min of inactivity. The current consumption in sleep is less than 7uA.The batteries are located on the back: Keeping the track of rotational angleThe rotational angle is tracked "by hardware“ rather by software meaning that the CPU has a lot more time at its disposal to do other tasks. For that I have used Angular Timer peripheral which is built into the used microcontroller PIC 16F1619.Input to the Angular Timer is a signal from Hall sensor DRV5033. The Hall sensor will generate a pulse every time a magnet passes by it. The Hall sensor is located at the spinning part of the device while the magnet is located on a static part for which the user holds the device. Since I used only one magnet that means that the Hall sensor will produce a pulse that is repeating every 360°.At the same time Angular Timer will generate 180 pulses per revolution in which every pulse represents 2° of rotation. I choose 180 pulses, and not 360° for instance, because I found 2° to be the perfect distance between the two columns of a printed character.The Angular Timer handles all that calculation automatically and will adjust automatically if the time between the two sensor pulses changes due to the rotation velocity changing. The positon of the magnet and Hall sensor is shown in the picture below.Remote AccessI wanted a way to change the displaying text dynamically and not by just hard coding it into the code. I have choose BLE because it uses a very small amount of energy and the used chip RN4871 is only 9 x 11.5 mm in dimension.Via BT link I am able to change the displaying text and its color - red or green. I can also monitor battery level to know when it is time to replace the batteries.The device can be controlled via computer application programmed in LabVIEW graphics programming environment or by using a freely available smartphone BLE applications which has the ability to directly write to the selected BLE Characteristics of a connected device.For sending the information from a PC/smartphone to the device I used one Service with three Characteristics, each identified by a Handle. PC ApplicationIn the top-left corner we have controls for starting up the National Instruments BLE server application. That is a command line application from NI which creates a bridge between BLE module on a computer and LabVIEW. It uses HTTP protocol to communicate. The reason for using this application is that LabVIEW only has native support for Bluetooth Classic and not for BLE. Upon successful connecting, the MAC address of a connected device is displayed on the right and that part is not grayed out anymore. There we can set the moving graphics and its color or just send some pattern to turn the LEDs on or off when the device is not spinning, I have used that for testing purposes. FontI generated English alphabet font using a freely available software "The Dot Factory“ but I needed to make a few modification before uploading it to the microcontroller.The reason for that is PCB layout which is "not in order“, meaning the output 0 from LED driver is maybe not connected to the LED 0 on the PCB, OUT 1 is not connected to LED 1 but rather to LED15 for instance, and etc.. The other reason is the software only allowed to generate 2x8bit font but the device has 16 LED for each color so I needed a 16bit high font.So I needed to make a software that would shift a few bits to compensate for PCB layout and combine them to one 16bit value.Because of that I developed a separate application in LabVIEW that takes the font generated in "The Dot Factory“ as input and transforms it to suit the needs of this project. Since the red and green LED PCB layouts are different I needed to use two fonts. The output for the green font is shown in the picture below. Programming jigOn the picture you can see the programming jig I have used to programe the device.Since, after every programming, I need to pick up the device and spin it to see the changes I didn't want to use standard programming headers or just solder the programming wires. I used Pogo pins which have a small spring inside them so they fit very tightly to the vias on the PCB.By using this setup I am able to program the microcontroller very fast and don’t need to worry about programming wires or the left-over solder after desoldering those wires. ConclusionTo summarize, I would like to point out that by using Angul Timer peripheral I successfully achieved a POV device which doesn’t depend on rotational velocity, so the quality of displayed graphics is kept the same at both higher and lower speeds.By careful design I managed to implement a low energy solution which will prolong the batteries life.As for the cons of this project I would like to point out there is no way to charge the used batteries, so battery replacement every now and then is required. No-name batteries from the local store lasted about 1 months with every-day use. Uses:This device can be used in a various promotional purposes or as teaching aid in electrotechnics or physics classes for instance.It can also be used as a therapeutic aid to increase attention for those with Attention Deficit Hyperactivity Disorder (ADHD) or calm symptoms of anxiety. The schematics and BOM are attached. The Gerbers have three separate circular boards - the front board (which holds the magnet), back side board, and a small circular ring to encrease the contact surface with the 608 bearing in the middle of the device.Also, I would like to thanks Simon from PCBWay for sponsoring the first version of the PCB :)3D output from Altium DesignerBill of Materials (BOM) in PDF format is available here:https://files.fm/down.php?cf&i=m6dx2ks8&n=BOM+%283%29.xlsxBOM in Excel format is available through "BOM(Bill of materials)" button on the top right of this page.

### DESCRIPTIONHi, everyone, this project is a wearable wich main function is a watch, but at the same time it can be a development board for other applications or gatgets. The main idea, is to have a very small (35mm x 35mm) wearable board that could be used with a battery. It's based on the Atmega328P microcontroller.Hola a todos, este proyecto es un wearable cuya función principal es la de un reloj de pulsera, pero al mismo tiempo puede ser usado como una tarjeta de desarrollo para otras aplicaciones o gatgets. La idea principal es tener una muy peque?a (35mm x 35mm) tarjeta wearable que pueda ser usada con una batería. El circuito está basado en el microcontrolador Atmega328P.### TECHNICAL DETAILS / COMPONENTSThe electronic design is based in a generic Arduino Nano with a CH340 USB controller, but with some modifications, so it can be operated at 3.3/3.7 volts, this way it can be powered with a small rechargable lithium battery. Other periphals can be conected trought the 6 analog I/O with the J3 connector or with the SPI protocol throught the J1 conector. The follow diagram show the base circuit.El dise?o electrónico está basado en un Arduino Nano genérico con un controlador USB CH340, pero con algunas modificaciones, de tal manera que pueda ser operado a 3.3/3,7 voltios, de esta manera pueder ser alimentado con una peque?a batería recargable de litio. Otros periféricos pueden ser conectados a través de las 6 Entradas/Salidas analógicas a través del conector J3, o con el protocolo SPI mediante el conector J1. El siguiente diagrama muestra el circuito base.Half of the device is an Arduino Nano and the other half is the clock style LED array. The follow diagram show the LED array and the connection with the Atmega328P.La mitad del circuito es un Arduino Nano y la otra mitad son los led con arreglo en forma de reloj. El siguiente diagrama muestra la manera en que están organizados los leds y la conexión con el Atmega328P.The follow image shows the expansion conectors pinout.La siguiente imagen muestra la disposición de los pines de los conectores.BILL OF MATERIALSC1 - 10ufC2 - 100nfC3 - 100nfC4 - 100nfC5 - 10ufC6 - 100nfC7 - 100nfC8 - 22pfC9 - 22pfC10 - 22pfC11 - 22pfD1:D16 - LEDPWR - LEDJ1 - Conector USB(UX60SC-MB-5ST)J2 - Conector(FH12-8S-1SH)J3 - Conector(FH12-6S-1SH)R1 - 1kR2 - 1kR3 - 10kR4 - 1kR5 - 1kR6 - 1kR7 - 470RR8 - 470RR9 - 470RRPWR - 470RS1 - Switch(B3U-wB)SL - B3SLSM - B3SLSR - B3SLU1 - Atmega328P (QFP-32 9x9x0.8)U2 - CH340 (SOP-16 7x1.27)U3 - LM7805 (SOT-89)U4 - MMBT3904 (SOT23)U5 - MMBT3904 (SOT23)U6 - MMBT3904 (SOT23)Y1 - 16Mhz CrystalY2 - 12Mhz Crystal### LEARN / TOPIC / BUILD INSTRUCTIONSFor the energy save the power led can be omited. WARNING: This PCB is a prototype and wasn't test. The test was made with a protoboard and an Arduino Nano. Also, the LEDs are placed in counterclockwise direction. The code showed below works with this configuration.Para ahorrar energía el led de encendido puede ser omitido. PRECAUCIóN: Este PCB es un prototipo y no ha sido probado. La prueba se realizó con un protoboard y un Arduino Nano. También, los leds han sido puestos en contrareloj. El código que se muestra a continuación funciona con esa configuración.Also, I designed a box that can be made with a 3D printer. The STL files are liested bellow.También, he dise?ado una caja que puede ser hecha con una impresora 3D. Los archivos STL se muestran abajo.DropBox STL file1 - BoxDropBox STL file2 - Cover### CODE// DuinO'Clock// 22/Nov/2018// Benjamín Alejandro Luna Ramírez// Versión 1.1#include <avr/sleep.h>// Constantsconst byte Button_Left = 2;const byte Button_Center = 3;const byte Button_Right = 4;const byte T1 = 5;const byte T2 = 6;const byte T3 = 7;const byte Led_Circle_Start = 7;const byte Preescaler_Divider = 7; // 7 = 128 times.const byte Preescaler_Frequency = 128;const int Time_Run = 500 / Preescaler_Frequency; // Time the leds are on when the device turn on.const int Time_Led_Blink = 400 / Preescaler_Frequency;const int Time_Led_Between = 200 / Preescaler_Frequency;// Variables globalesbyte volatile timeHour = 1;byte volatile timeMinute = 0;byte volatile timeSecond = 0;int volatile timeMiliseconds = 0;/* currentFunction values are: 0:none 1:Showing Hour 2:Changing Hour*/byte volatile currentFunction = 0;void setup() { // put your setup code here, to run once: CLKPR = 0b10000000; CLKPR = Preescaler_Divider; // Buttons pinMode(Button_Left, INPUT_PULLUP); pinMode(Button_Center, INPUT_PULLUP); pinMode(Button_Right, INPUT_PULLUP);// Transistors pinMode(T1, OUTPUT); pinMode(T2, OUTPUT); pinMode(T3, OUTPUT);// Leds pinMode(Led_Circle_Start + 1, OUTPUT); pinMode(Led_Circle_Start + 2, OUTPUT); pinMode(Led_Circle_Start + 3, OUTPUT); pinMode(Led_Circle_Start + 4, OUTPUT); pinMode(Led_Circle_Start + 5, OUTPUT); pinMode(Led_Circle_Start + 6, OUTPUT);// Enciendo los leds menos significativos en secuencia para indicar que está encendido. digitalWrite(T3, HIGH); digitalWrite(Led_Circle_Start + 1, HIGH); delay(Time_Run); digitalWrite(Led_Circle_Start + 1, LOW); digitalWrite(Led_Circle_Start + 2, HIGH); delay(Time_Run); digitalWrite(Led_Circle_Start + 2, LOW); digitalWrite(Led_Circle_Start + 3, HIGH); delay(Time_Run); digitalWrite(Led_Circle_Start + 3, LOW); digitalWrite(Led_Circle_Start + 4, HIGH); delay(Time_Run); digitalWrite(Led_Circle_Start + 4, LOW); digitalWrite(T3, LOW);// Disable interrupts before changing the preescaler value. noInterrupts();// Synchronous mode. ASSR = (ASSR & 0b11011111);// Operate in CTC mode and preescaler. TCCR2B = 0b00000111; TCCR2A = 0b00000010; TCNT2 = 0;// 10 milisegundos (16,000,000 / 1024 * 0.01) = 156 OCR2A = 255; TIMSK2 = 0b00000010; interrupts(); SleepDevice();}void SleepDevice(){// Attach the interrupts to the pins. attachInterrupt(digitalPinToInterrupt(Button_Center), ShowHour, LOW); attachInterrupt(digitalPinToInterrupt(Button_Left), ChangeHour, LOW);// Enter Power-Save Sleep mode. SMCR = 0b00000111; sleep_cpu();// Disable sleep after waking up and detach interrupt. SMCR = 0b00000000; detachInterrupt(digitalPinToInterrupt(Button_Center)); attachInterrupt(digitalPinToInterrupt(Button_Left), ChangeHour, LOW);}void loop() { switch(currentFunction) {// Showing the hour. case 1: LightHour(); delay(Time_Led_Blink); ClearLeds(); delay(Time_Led_Between); LightMostSignificantMinute(); delay(Time_Led_Blink); ClearLeds(); delay(Time_Led_Between); LightLessSignificantMinute(); delay(Time_Led_Blink); ClearLeds(); currentFunction = 0; break;// Changing hour. case 2: byte next = 0;// Changing hour// Wait for the button. while(digitalRead(Button_Left) == LOW) { delay(1); }// >> Show the current hour. LightHour(); while(next == 0) { // Probes if one of the buttons has been pressed. if(digitalRead(Button_Left) == LOW) { next = 1; while(digitalRead(Button_Left) == LOW) { delay(1); } }else if(digitalRead(Button_Right) == LOW){ if(timeHour <= 11) timeHour++; else timeHour = 1;// >> Show the current hour. LightHour(); while(digitalRead(Button_Right) == LOW) { delay(1); } } } next = 0;// >> Show the current most significant minute. LightMostSignificantMinute();// Changing most significant minute. while(next == 0) {// Probes if one of the buttons has been pressed. if(digitalRead(Button_Left) == LOW) { next = 1; while(digitalRead(Button_Left) == LOW) { delay(1); } }else if(digitalRead(Button_Right) == LOW){ if(timeMinute < 55) timeMinute += 5; else timeMinute += 5 - 60; LightMostSignificantMinute(); while(digitalRead(Button_Right) == LOW) { delay(1); } } } next = 0;// >> Show the current less significant minute. LightLessSignificantMinute();// Changing less significant minute. while(next == 0) {// Probes if one of the buttons has been pressed. if(digitalRead(Button_Left) == LOW) { next = 1; while(digitalRead(Button_Left) == LOW) { delay(1); } }else if(digitalRead(Button_Right) == LOW){ if((timeMinute % 5) < 4) timeMinute++; else timeMinute -= 4; LightLessSignificantMinute(); while(digitalRead(Button_Right) == LOW) { delay(1); } } } ClearLeds(); currentFunction = 0; break; } SleepDevice();}void LightHour(){ ClearLeds();// Show the led for the hour. byte column = T2; byte mostSignificantLed = 0; if(timeHour == 12) { mostSignificantLed = 6; }else if(timeHour > 5){ column = T1; mostSignificantLed = 12 - timeHour; }else{ mostSignificantLed = 6 - timeHour; } digitalWrite(column, HIGH); digitalWrite(mostSignificantLed + Led_Circle_Start, HIGH);}void LightMostSignificantMinute(){ ClearLeds();// Show the leds for the minutes. byte column = T1; byte mostSignificantLed = 0; if(timeMinute < 5) { column = T2; }else if(timeMinute >= 30){ column = T1; }else{ column = T2; } mostSignificantLed = timeMinute / 5; if(mostSignificantLed > 5) { mostSignificantLed = 12 - mostSignificantLed; }else if(mostSignificantLed == 0){ mostSignificantLed = 6; }else{ mostSignificantLed = 6 - mostSignificantLed; } digitalWrite(column, HIGH); digitalWrite(mostSignificantLed + Led_Circle_Start, HIGH);}void LightLessSignificantMinute(){ ClearLeds(); byte mostSignificantLed = timeMinute / 5; byte lessSignificantLed = timeMinute % 5; if(lessSignificantLed > 0) { if(lessSignificantLed < 4) lessSignificantLed = 4 - lessSignificantLed; digitalWrite(T3, HIGH); digitalWrite(lessSignificantLed + Led_Circle_Start, HIGH); }}void ClearLeds(){ digitalWrite(T1, LOW); digitalWrite(T2, LOW); digitalWrite(T3, LOW); digitalWrite(Led_Circle_Start + 1, LOW); digitalWrite(Led_Circle_Start + 2, LOW); digitalWrite(Led_Circle_Start + 3, LOW); digitalWrite(Led_Circle_Start + 4, LOW); digitalWrite(Led_Circle_Start + 5, LOW); digitalWrite(Led_Circle_Start + 6, LOW);}ISR(TIMER2_COMPA_vect){ timeMiliseconds += 2088; if(timeMiliseconds >= 1000) { while(timeMiliseconds >= 1000) { timeMiliseconds -= 1000; timeSecond++; } if(timeSecond >= 60) { timeSecond -= 60; timeMinute++; if(timeMinute == 60) { timeMinute = 0; timeHour++; if(timeHour == 13) { timeHour = 1; } } } }}void ShowHour() { detachInterrupt(digitalPinToInterrupt(Button_Center)); detachInterrupt(digitalPinToInterrupt(Button_Left)); currentFunction = 1;}void ChangeHour() { detachInterrupt(digitalPinToInterrupt(Button_Left)); detachInterrupt(digitalPinToInterrupt(Button_Center)); currentFunction = 2;}