1 Introduction
As, February 30, 2012 Philips sells the latest high-tech Hue series LED lights in AppleStore, and will only be sold by apples. The HUE series will be customized, and the LEDs of the red blue green three primary colors through a bulb can be mixed with 16 million colors of colors. The entire process is completely controlled by app on the iPhone. It has thus triggered a new thinking of intelligent light control development, and domestic relevant people also studied. Considering that hue is wireless control, domestic WiFi is not popular, this study uses more common Bluetooth technology, using mobile Bluetooth and single-chip communication to generate a tonarchic duty-free PWM wave signal control LED drive circuit to realize the dimming of the LED and DIY toning.
2. Pulse Wide System (PWM) dimming technology
PWM dimming is a dimming technique using a simple digital pulse, repeating switching LED driver. The applicant's system only needs to provide wide, narrow different digital pulses, simply changing the output current, thereby adjusting the brightness of the LED. The advantage of PWM dimming is that the dimming range is large, as long as the bandwidth is sufficient, any analog value can be encoded using PWM, and PWM dimming can ensure the brightness of the LED while accurately controlling the brightness of the LED.
2.1 Pulse Wide System (PWM) dimming principle
Using people's eye visual inertness, pressing the fixed frequency operating duty cycle to achieve the LED brightness adjustment, as long as the dimming ratio is greater than 200 Hz, it will not feel the flash of the LED. Specific dimming implementation, by controlling the brightness of the LED, thereby controlling the brightness of the LED, from electrical power to control the effective value of the current in a certain period. This method does not change the voltage and current size while changing the current valid value, so that the LED of the LED is not achieved by analog dimming and thyristor tuning.
2.2 duty cycle
The duty cycle is the time ratio of high levels within one cycle. The duty cycle of square wave is 50%, the duty cycle is 0.5, indicating that the timing of the positive level is 0.5 cycles.
TS is a pulse cycle
TW is a pulse width
Duty cycle τ = TW / TS × 100.
The interpretation of the duty cycle can be summarized as the following:
1) In a string of ideal pulse sequences (such as square wave), the duration of the positive pulse and the ratio of the pulse total cycle.
2) The ratio of time and total time for pulses for pulses in a continuous working time.
3) In the periodic phenomenon, the time and total time of the total time.
That is, the effective time of the circuit release energy and the total release time.
2.3 dimming ratio
The dimming ratio is calculated as follows:
FOper = operating frequency
FPWM = dimming frequency
Dimming ratio = FOPER / FPWM
In fact, the minimum effective duty cycle of dimming, such as FOper = 100kHz; fpwm = 200Hz, the dimming ratio is:
100K / 200 = 500.
3. Composition of Bluetooth module
3.1 Bluetooth technology foundation
The founder of Bluetooth is Swedish Ericsson Company, Bluetooth technology is an open global specification for wireless data and voice communication. It is based on low-cost near-distance wireless connections to set a special connection to the mobile device communication environment. The mobile phones have become frequently managed between Bluetooth, which has become a common sense, which transforms mobile phone to the remote control to bring unlimited convenience to people's lives.
Bluetooth technology consists of three parts, including Bluetooth radio technology, Bluetooth protocol stack, and Bluetooth interoperability.
3.1.1 Bluetooth radio technology
Bluetooth radio works in global 2.4GHzism (ie, industrial, scientific, medicine) frequency bands, support full-duplex transmission, using IEEE802.15 protocol. Bluetooth equipment is connected, strong anti-interference ability, easy to use [2]
3.1.2 Bluetooth protocol stack
The Bluetooth protocol stack contains a software stack and a hardware stack. Bluetooth Hardware Agreement Stack Provided by Bluetooth hardware, Bluetooth software protocol stack is implemented by software. The Bluetooth Software Agreement Stack provides Java Bluetooth API to use the Open personnel.
3.1.3 Bluetooth interoperability
Bluetooth interoperability includes three aspects: 1 General Access PROFILE defines the device management functionality; 2 Service discovery application PROFILES defines the content of service discovery; 3 serial poplet defines the ability of interoperability devices and analog serial cables 3.2 HC- O6 Bluetooth module.
BC04 external 8M Flash, with EDR module HC-06 for civilian level, compatible with HC-04 industrial grade. Among them, the TX pin of the HC-06 module is connected to the P3.0 pin of the STC15F204EA microcontroller, and the RX pin is connected to P3.1. The HC-06 module receives the data sent by the mobile phone and communicates with the microcontroller through the serial port TR, TX pin.
Bluetooth 2.0 with EDR, 2MBPS-3MBPS modulation, built-in 2.4GHz antenna, external 8Mbit Flash, low voltage 3.3V work (3.1V ~ 4.2V) pairing 30 ~ 40mA fluctuations, pairing communication 8mA, optional PIO control standard HCI port (UART OR USB), digital 2.4GHz wireless receiving, CSR BC04 Bluetooth chip technology, adaptive frequency hopping technology, Bluetooth Class 2 power level, operating temperature is -25 to +75, coordinate interference is 2.4MHz, launch Power 3dBm, the effective control distance is 10m.
4. Mobile app design
4.1 Bluetooth connection related program design
First, the local Bluetooth device is initialized, establish a LocalDevice class, including obtaining a local device instance, a Bluetooth name, setting discovery mode, and obtains an discovery agent. Create a public int bts_init () class function to achieve Bluetooth initialization, looking for default Bluetooth devices, open Bluetooth.
Start the Bluetooth device search, create a public voidbts_startscan () class function, start looking for slave Bluetooth devices, registering a search function, creating a public int bts_connecttodevice (String DeviceAddress) class function to connect to a specified Bluetooth device.
Create public int BTS_SendDates (Stringbuffer) class functions send strings to achieve a good connection is a Bluetooth device, create public int BTS_Finish () function ends the Bluetooth communication class, and finally create a broadcast receiving ACTION_FOUND BroadcastReceiver privatefinal BroadcastReceiver mReceiver = newBroadcastReceiver ().
4.2 Control signal related programming
First create a class for a control signal publicclass PwmcontrolActivity extends Activity {}, which includes creating function interface class public voidonCreate (BundlesavedIn stan ceState) {}, a function of transmitting a control signal based public void onStop TrackingTouch (SeekBar seekBar) {}.
Create a class class initthread extends thread {}, implement the resource load thread, create a public initThread (PWMControlActivity Act) {} class function for the conversion between four-channel signals, implement the public void run () thread body with the Bluetooth program interface, The class function for software exits Public BooleanonkeyDown (Int Keyco de, KeyEvent Event).
5. Single chip control signal design
5.1 Hardware circuit design
According to Figure 1, the hardware circuit uses the STC15F204EA microcomputer as the master, the TXD of the CH-06 Bluetooth module is connected to the microcontroller 11 pin P3.0 connection, and the RXD is connected to P3.1, and the Bluetooth serial communication connection is achieved. P1.0, P1.1, P1.2, P1.3 Output four-way movable PWM signal, use one L298 chip to isolate the single-chip control signal and the LED power supply, avoiding single-chip load capacity Weak disadvantages to achieve drive high power LEDs.
Figure 1 System block diagram
5.2 programming
The main function flow chart is shown in Figure 2, and after defining the correlation variable and related function declaration, design the serial port communication function, set the timer 1 interrupt, the interrupt function is the duty cycle control function, then design the data reception function, when the serial service function When the data is received, the data is sent to the data receiving function, and then the accepted character data is transmitted through the character transition function, and then determines which signal is determined by the flag ICOMMDTYPE, when there is no flag signal, it is looped, Check to the corresponding flag signal, then execute the communication between the Bluetooth module and the single-chip communication between the Bluetooth module, the serial port is implemented, the serial port is standard: baud rate 9600, write a serial initial function Void UART_Init (), initialization Sign, and register, then write interrupt receiving functions void TM0 () Interrupt 1 using 1, receive data from the serial port. Set the timer 1 interrupt and write the interrupt service function void TM1 () interrupt 3 using1 to implement the duty cycle control of P w M. Write a data reception function char gameUartData (), send the data received in the interrupt reception function here, waiting for the receiving data function void waitforchars (unsigned charicount, char * dest) by calling the data reception function char GetuartData (), send the phone to Data is loaded to a variable array of defined variables, and then transform the character data into a number through the character transition function, and the character data is converted to a number. If you want to control which PWM wave is to control, then the corresponding data is transmitted to the control. The interrupt service function of the duty cycle changes its duty cycle.
Figure 2 Main function flow chart
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