How to interface LEDs with 8051 microcontroller (AT89C51)

This article introduces you to the very basic operation of taking an output from the microcontroller AT89C51. It demonstrates the principle behind interfacing LEDs with 8051 microcontroller. Here we have demonstrated the aforesaid principles by blinking LEDs continuously i.e., switching them on and off.

AT89C51, which belongs to the family of 8051 series of microcontrollers, is very commonly used by a large community of hobbyist and engineers. Its simplicity and ease of programming with inbuilt features easily makes its position in the top preferred list of  microcontroller for both beginners and advanced user.

LEDs are by far the most widely used means of taking output. They find huge application as indicators during experimentations to check the validity of results at different stages. They are very cheap and easily available in a variety of shape, size and colors.

The principle of operation of LEDs is simple. The commonly available LEDs have a drop voltage of 1.7 V and need 10 mA to glow at full intensity. The following circuit describes “how to glow an led”.

 

 

The value of resistance R can be calculated using the equation, R= (V-1.7)/10 mA. Since most of the controllers work on 5V, so substituting V= 5V, the value of resistance comes out to be 330 ohm. The resistance 220 ohm, 470 ohm is commonly used substitute in case 330 ohm is not available.

  

AT89C51 is a 40 pin microcontroller which belongs to 8051 series of microcontroller. It has four ports each of 8 bits P0, P1, P2 and P3.The AT89C51 has 4K bytes of programmable flash. The port P0 covers the pin 32 to pin 39, the port P1 covers the pin 1 to pin 8, the port P2 covers the pin 21 to pin 28 and the port P3 covers the pin 10 to pin 17. Pin 9 is the reset pin. The reset is active high. Whenever the controller is given supply, the reset pin must be given a high signal to reset the controller and bring the program counter to the starting address 0x0000. The controller can be reset by manually connecting a switch or by connecting a combination of resistor and capacitor as shown in the circuit diagram. A 12 MHz crystal is connected between pin 18 pin 19. Pin 40 is Vcc and pin 20 is ground. Pin 31, is connected to Vcc as we are using the internal memory of the controller.

LEDs are connected to the port P0. LEDs need approximately 10mA current to flow through them in order to glow at maximum intensity. However the output of the controller is not sufficient enough to drive the LEDs, so if the positive leg of the LED is connected to the pin and the negative to ground as shown in the figure, the LED will not glow at full illumination.

 

 

To overcome this problem LEDs are connected in the reverse order and they run on negative logic i.e., whenever 1 is given on any pin of the port, the LED will switch off and when logic 0 is provided the LED will glow at full intensity.

 

As soon as we provide supply to the controller, the LEDs start blinking i.e., they become on for a certain time duration and then become off for the same time duration. This delay is provided by calling the delay function. The values inside the delay function have been set to provide a delay in multiples of millisecond (delay (100) will provide a delay of 100 millisecond).

CIRCUIT DIAGRAM>>>

CODE>>>

/  Program to blink the LEDs. LEDs are connected to port 0.

#include<reg51.h>

void delay(int time)        //This function produces a delay in msec.
{
    int i,j;
    for(i=0;i<time;i++)
     for(j=0;j<1275;j++);
}

void main()
{
     while(1)
     {
          P0=0x00;
          delay(50);
          P0=0xff;
          delay(50);
     }
}

Interrupts & Programming 8051 Hardware Interrupts

Interrupt is one of the most important and powerful concepts and features in microcontroller/processor applications. Almost all the real world and real time systems built around microcontrollers and microprocessors make use of interrupts.

What is an Interrupt

The interrupts refer to a notification, communicated to the controller, by a hardware device or software, on receipt of which controller momentarily stops and responds to the interrupt. Whenever an interrupt occurs the controller completes the execution of the current instruction and starts the execution of an

Interrupt Service Routine (ISR) or Interrupt Handler. ISR is a piece of code that tells the processor or controller what to do when the interrupt occurs. After the execution of ISR, controller returns back to the instruction it has jumped from (before the interrupt was received).

Why need interrupts

An application built around microcontrollers generally has the following structure. It takes input from devices like keypad, ADC etc; processes the input using certain algorithm; and generates an output which is either displayed using devices like seven segment, LCD or used further to operate other devices like motors etc. In such designs, controllers interact with the inbuilt devices like timers and other interfaced peripherals like sensors, serial port etc. The programmer needs to monitor their status regularly like whether the sensor is giving output, whether a signal has been received or transmitted, whether timer has finished counting, or if an interfaced device needs service from the controller, and so on. This state of continuous monitoring is known as polling.

In polling, the microcontroller keeps checking the status of other devices; and while doing so it does no other operation and consumes all its processing time for monitoring. This problem can be addressed by using interrupts. In interrupt method, the controller responds to only when an interruption occurs. Thus in interrupt method, controller is not required to regularly monitor the status (flags, signals etc.) of interfaced and inbuilt devices.

To understand the difference better, consider the following. The polling method is very much similar to a salesperson. The salesman goes door-to-door requesting to buy its product or service. Like controller keeps monitoring the flags or signals one by one for all devices and caters to whichever needs its service. Interrupt, on the other hand, is very similar to a shopkeeper. Whosoever needs a service or product goes to him and apprises him of his/her needs. In our case, when the flags or signals are received, they notify the controller that they need its service.

Hardware and Software interrupt

The interrupts in a controller can be either hardware or software. If the interrupts are generated by the controller’s inbuilt devices, like timer interrupts; or by the interfaced devices, they are called the hardware interrupts. If the interrupts are generated by a piece of code, they are termed as software interrupts.

Multiple interrupts

What would happen if multiple interrupts are received by a microcontroller at the same instant? In such a case, the controller assigns priorities to the interrupts. Thus the interrupt with the highest priority is served first. However the priority of interrupts can be changed configuring the appropriate registers in the code.

8051 Interrupts

The 8051 controller has six hardware interrupts of which five are available to the programmer. These are as follows:

1. RESET interrupt – This is also known as Power on Reset (POR). When the RESET interrupt is received, the controller restarts executing code from 0000H location. This is an interrupt which is not available to or, better to say, need not be available to the programmer.

2. Timer interrupts – Each Timer is associated with a Timer interrupt. A timer interrupt notifies the microcontroller that the corresponding Timer has finished counting.

3. External interrupts – There are two external interrupts EX0 and EX1 to serve external devices. Both these interrupts are active low. In AT89C51, P3.2 (INT0) and P3.3 (INT1) pins are available for external interrupts 0 and 1 respectively. An external interrupt notifies the microcontroller that an external device needs its service.

4. Serial interrupt – This interrupt is used for serial communication. When enabled, it notifies the controller whether a byte has been received or transmitted.

How is an interrupt serviced?

Every interrupt is assigned a fixed memory area inside the processor/controller. The Interrupt Vector Table (IVT) holds the starting address of the memory area assigned to it (corresponding to every interrupt).

The interrupt vector table (IVT) for AT89C51 interrupts is as follows :

Interrupt	ROM Location (Hex)	Pin	Flag clearing
Reset	0000	9	Auto
External interrupt 0	0003	12	Auto
Timer interrupt 0	000B	–	Auto
External interrupt 1	0013	13	Auto
Timer interrupt 1	001B	–	Auto
Serial COM interrupt	0023	–	Programmer clears it

When an interrupt is received, the controller stops after executing the current instruction. It transfers the content of program counter into stack. It also stores the current status of the interrupts internally but not on stack. After this, it jumps to the memory location specified by Interrupt Vector Table (IVT). After that the code written on that memory area gets executed. This code is known as the Interrupt Service Routine (ISR) or interrupt handler. ISR is a code written by the programmer to handle or service the interrupt.

Programming Interrupts

While programming interrupts, first thing to do is to specify the microcontroller which interrupts must be served. This is done by configuring the Interrupt Enable (IE) register which enables or disables the various available interrupts. The Interrupt Enable register has following bits to enable/disable the hardware interrupts of the 8051 controller.

To enable any of the interrupts, first the EA bit must be set to 1. After that the bits corresponding to the desired interrupts are enabled. ET0, ET1 and ET2 bits are used to enable the Timer Interrupts 0, 1 and 2, respectively. In AT89C51, there are only two timers, so ET2 is not used. EX0 and EX1 are used to enable the external interrupts 0 and 1. ES is used for serial interrupt.

EA bit acts as a lock bit. If any of the interrupt bits are enabled but EA bit is not set, the interrupt will not function. By default all the interrupts are in disabled mode.

Note that the IE register is bit addressable and individual interrupt bits can also be accessed.

For example –

IE = 0x81; enables External Interrupt0 (EX0)

IE = 0x88; enables Serial Interrupt

Setting the bits of IE register is necessary and sufficient to enable the interrupts. Next step is to specify the controller what to do when an interrupt occurs. This is done by writing a subroutine or function for the interrupt. This is the ISR and gets automatically called when an interrupt occurs. It is not required to call the Interrupt Subroutine explicitly in the code.

An important thing is that the definition of a subroutine must have the keyword interrupt followed by the interrupt number. A subroutine for a particular interrupt is identified by this number. These subroutine numbers corresponding to different interrupts are tabulated below.

Number	Interrupt	Symbol
0	External0	EX0
1	Timer0	IT0
2	External1	EX1
3	Timer1	IT1
4	Serial	ES
5	Timer2	ET2

For example : Interrupt routine for Timer1

void ISR_timer1(void) interrupt 3
{
	<Body of ISR>
}

For example : Interrupt routine for External Interrupt0 (EX0)

void ISR_ex0(void) interrupt 0
{
	<Body of ISR>
}

Note that the interrupt subroutines always have void return type. They never return a value.

1. Programming Timer Interrupts

The timer interrupts IT0 and IT1 are related to Timers 0 and 1, respectively. (Please refer 8051 Timers for details on Timer registers and modes.) The interrupt programming for timers involves following steps :

1.                  Configure TMOD register to select timer(s) and its/their mode.

2.                  Load initial values in THx and TLx for mode 0 and 1; or in THx only for mode 2.

3.                  Enable Timer Interrupt by configuring bits of IE register.

4.                  Start timer by setting timer run bit TRx.

5.                  Write subroutine for Timer Interrupt. The interrupt number is 1 for Timer0 and 3 for Timer1.

Note that it is not required to clear timer flag TFx.

6.                 To stop the timer, clear TRx in the end of subroutine. Otherwise it will restart from 0000H in case of modes 0 or 1 and from initial values in case of mode 2.

7.                 If the Timer has to run again and again, it is required to reload initial values within the routine itself (in case of mode 0 and 1). Otherwise after one cycle timer will start counting from 0000H.

Example code

Timer interrupt to blink an LED; Time delay in mode1 using interrupt method

// Use of Timer mode0 for blinking LED using interrupt method
// XTAL frequency 11.0592MHz 
#include<reg51.h>
sbit LED = P1^0; 		//LED connected to D0 of port 1

void timer(void) interrupt 1 		//interrupt no. 1 for Timer 0
{
	led=~led; 		//toggle LED on interrupt
	TH0=0xFC;		// initial values loaded to timer
	TL0=0x66;
}
main()
{
	TMOD = 0x01; 		// mode1 of Timer0
	TH0 = 0xFC;		// initial values loaded to timer
	TL0 = 0x66;
	IE = 0x82;		// enable interrupt
	TR0 = 1;		//start timer
	while(1);		// do nothing  
}

2. Programming External Interrupts

The external interrupts are the interrupts received from the (external) devices interfaced with the microcontroller. They are received at INTx pins of the controller. These can be level triggered or edge triggered. In level triggered, interrupt is enabled for a low at INTx pin; while in case of edge triggering, interrupt is enabled for a high to low transition at INTx pin. The edge or level trigger is decided by the TCON register. The TCON register has following bits:

Setting the IT0 and IT1 bits make the external interrupt 0 and 1 edge triggered respectively. By default these bits are cleared and so external interrupt is level triggered.

Note : For a level trigger interrupt, the INTx pin must remain low until the start of the ISR and should return to high before the end of ISR. If the low at INTx pin goes high before the start of ISR, interrupt will not be generated. Also if the INTx pin remains low even after the end of ISR, the interrupt will be generated once again. This is the reason why level trigger interrupt (low) at INTx pin must be four machine cycles long and not greater than or smaller than this.

Following are the steps for using external interrupt :

1.        Enable external interrupt by configuring IE register.

2.        Write routine for external interrupt. The interrupt number is 0 for EX0 and 2 for EX1 respectively.

Example code

//Level trigger external interrupt
void main()
{
	IE = 0x81;
	while(1);
}
void ISR_ex0(void) interrupt 0
{
	<body of interrupt>
}

Example code

//Edge trigger external interrupt
void main()
{
	IE = 0x84;
	IT1 = 1;
	while(1);
}
void ISR_ex1(void) interrupt 2
{
	<body of interrupt>
}

3. Programming Serial Interrupt

To use the serial interrupt the ES bit along with the EA bit is set. Whenever one byte of data is sent or received, the serial interrupt is generated and the TI or RI flag goes high. Here, the TI or RI flag needs to be cleared explicitly in the interrupt routine (written for the Serial Interrupt).

The programming of the Serial Interrupt involves the following steps:

1.        Enable the Serial Interrupt (configure the IE register).

2.        Configure SCON register.

3.        Write routine or function for the Serial Interrupt. The interrupt number is 4.

4.        Clear the RI or TI flag within the routine.

Example code

Send ‘A’ from serial port with the use of interrupt

// Sending ‘A’ through serial port with interrupt
// XTAL frequency 11.0592MHz 
void main()
{
	TMOD = 0x20;
	TH1 = -1;
	SCON = 0x50;
	TR1 = 1;
	IE = 0x90;
	while(1);
}
void ISR_sc(void) interrupt 4
{
	if(TI==1)
	{
		SBUF = ‘A’;
		TI = 0;
	}
	else
		RI = 0;
}

Example code

// Receive data from serial port through interrupt
// XTAL frequency 11.0592MHz 
void main()
{
	TMOD = 0x20;
	TH1 = -1;
	SCON = 0x50;
	TR1 = 1;
	IE = 0x90;
	while(1);
}
void ISR_sc(void) interrupt 4
{
	unsigned char val;
	if(TI==1)
	{
		TI = 0;
	}
	else
	{
		val = SBUF;
		RI = 0;
	}
}

Programming multiple interrupts

Multiple interrupts can be enabled by setting more than one interrupts in the IE register. If more than one interrupts occur at the same time, the interrupts will be serviced in order of their priority. By default the interrupts have the following priorities in descending order:

Default priority order of Interrupts
Interrupt	Symbol
External0	EX0
Timer0	ET0
External1	EX1
Timer1	ET1
Serial	ES
Timer2	ET2

The priority of the interrupts can be changed by programming the bits of Interrupt Priority (IP) register. The IP register has the following bit configuration:

First two MSBs are reserved. The remaining bits are the priority bits for the available interrupts.

Bit	Interrupt	Symbol
PX0	External0	EX0
PT0	Timer0	ET0
PX1	External1	EX1
PT1	Timer1	ET1
PS	Serial	ES
PT2	Timer2	ET2

Setting a particular bit in IP register makes the corresponding interrupt of the higher priority.

For example, IP = 0x08; will make Timer1 priority higher. So the interrupt priority order will change as follows (in descending order):

IP = 0x08
Default Priority	Changed Priority
EX0	ET1
ET0	EX0
EX1	ET0
ET1	EX1
ES	ES
ET2	ET2

More than one bit in IP register can also be set. In such a case, the higher priority interrupts will follow the sequence as they follow in default case.

For example, IP = 0x0A; will make Timer0 and Timer1 priorities higher. So the interrupt priority order will change as follows (in descending order):

IP = 0x0A
Default Priority	Changed Priority
EX0	ET0
ET0	ET1
EX1	EX0
ET1	EX1
ES	ES
ET2	ET2

Note that the Timer 0 and 1 have been assigned higher priorities in the same sequence as they follow in default case.

Example code

// Toggle LEDs by Timer and External Interrupt
#include<reg51.h>
sbit led_timercontrol = P1^0;
sbit led_externalcontrol = P1^0;
void external(void) interrupt 0
{
	led_externalcontrol = ~ led_externalcontrol;
}

void timer(void) interrupt 1
{
	led_timercontrol = ~ led_timercontrol; 
}
main()
{
	TMOD = 0x01;
	TH0 = 0x00;
	TL0 = 0x00;
	IE = 0x83;
	TR0 = 1;	
	while(1);
}

Wireless motor control through RF

 

Wireless remote controlled toy cars work on the concept explained here. Motor control through RF communication is a very interesting application and is widely used in robotics, electronics toys, automation systems etc. This topic covers the way DC motors can be driven by using the controls from a distant place. The controls are transferred from one end to another by employing an RF module.

The remote control application of RF has been extended to operate a motor driver which in turn controls the direction of motors.

 

This circuit uses RF module to control DC motors through a motor driver IC L293D. Transmission is enabled by giving a low bit to pin14 (TE, active low) of encoder HT12E. The controls for motor are first sent to HT12E. Pins 10 and 11 (D0-D1) are used to control one motor while pins 12 and 13 (D2-D3) to control another motor. The data signals of encoder HT12E work on negative logic. Therefore a particular signal is sent by giving a low bit to the corresponding data pin of encoder.

The parallel signals generated at transmission end are first encoded (into serial format) by HT12E and then transferred through RF transmitter (434 MHz) at a baud rate of around 1-10 kbps. The same signals are acquired by RF receiver after which it is decoded by HT12D. For more details, refer RF remote control.

Since the encoder/decoder pair used here works on negative logic, the decoded signals are fed to an inverter (NOT gate) IC 74LS04. The proper (inverted) signals are then supplied to L293D. L293D contains two inbuilt H-bridge driver circuits to drive two DC motors simultaneously, both in forward and reverse direction.

The motor operations of two motors can be controlled by input logic at pins 2 & 7 and pins 10 & 15. Input logic 00 or 11 will stop the corresponding motor. Logic 01 and 10 will rotate it in clockwise and anticlockwise directions, respectively. Thus, depending upon the signals generated at the transmission end, the two motors can be rotated in desired directions.

Circuit Diagram:

RF module

The RF module, as the name suggests, operates at Radio Frequency. The corresponding frequency range varies between 30 kHz & 300 GHz. In this RF system, the digital data is represented as variations in the amplitude of carrier wave. This kind of modulation is known as Amplitude Shift Keying (ASK).

Transmission through RF is better than IR (infrared) because of many reasons. Firstly, signals through RF can travel through larger distances making it suitable for long range applications. Also, while IR mostly operates in line-of-sight mode, RF signals can travel even when there is an obstruction between transmitter & receiver. Next, RF transmission is more strong and reliable than IR transmission. RF communication uses a specific frequency unlike IR signals which are affected by other IR emitting sources.

This RF module comprises of an RF Transmitter and an RF Receiver. The transmitter/receiver (Tx/Rx) pair operates at a frequency of 434 MHz. An RF transmitter receives serial data and transmits it wirelessly through RF through its antenna connected at pin4. The transmission occurs at the rate of 1Kbps – 10Kbps.The transmitted data is received by an RF receiver operating at the same frequency as that of the transmitter.

The RF module is often used alongwith a pair of encoder/decoder. The encoder is used for encoding parallel data for transmission feed while reception is decoded by a decoder. HT12E–HT12D, HT640-HT648, etc. are some commonly used encoder/decoder pair ICs.

Pin Diagram:

Pin Description:

RF Transmitter

Pin No	Function	Name
1	Ground (0V)	Ground
2	Serial data input pin	Data
3	Supply voltage; 5V	Vcc
4	Antenna output pin	ANT

RF Receiver

Pin No	Function	Name
1	Ground (0V)	Ground
2	Serial data output pin	Data
3	Linear output pin; not connected	NC
4	Supply voltage; 5V	Vcc
5	Supply voltage; 5V	Vcc
6	Ground (0V)	Ground
7	Ground (0V)	Ground
8	Antenna input pin	ANT

Wireless power transmission system with increased output voltage

The invention relates to a system for wireless power transmission, which makes it possible to generate an increased voltage on the receiver side using a radio signal that is optimized for this purpose and thereby permits operation particularly of digital semiconductor components in the receiver even if the receiver does not have a power supply of its own.

Representative Image:

Claims:

What is claimed is:

1. A device for wireless power transmission, including a system for supplying transponders, comprising: at least one high-frequency transmitter that transmits a transmitted high-frequency output signal, and at least one high-frequency receiver that receives the transmitted high-frequency output signal, wherein the at least one high-frequency transmitter is connected to at least one antenna, and the at least one high-frequency receiver is connected to at least one antenna, wherein the receiver obtains its operating power from the transmitted high-frequency output signal from said transmitter, wherein (1) the transmitted high-frequency output signal from the transmitter is modulated with at least one converter clock suitable for a DC-DC converter, (2) the receiver has at least one detector for demodulating the at least one converter clock from the transmitted high frequency output signal, (3),the receiver generates a DC operating voltage for the DC-DC converter from the high-frequency output signal using at least one of a rectifier and the at least one detector, (4) the DC-DC converter, using the at least one converter clock, and generating another DC voltage to operate further circuit elements.

2. The device as claimed in claim 1, wherein the high frequency transmitter is pulse modulated or amplitude modulated.

3. The device as claimed in claim 1, wherein a DC operating voltage for the DC-DC converter is derived from a common rectifier and detector together with the converter clock, in that a common output signal is processed by means of at least one of a low-pass filter and at least one diode coupling and a buffer capacitor.

4. The device as claimed in claim 1, wherein the at least one converter clock for the DC-DC converter is derived from a common rectifier and detector together with a DC operating voltage for the DC-DC converter, in that a common output signal is processed by means of at least one of a high-pass filter and at least one band pas filter.

5. The device as claimed in claim 1, wherein a voltage level of the at least one converter clock is increase by impedance conversion by means of one of a transmitter and resonant circuit.

6. A device for wireless power transmission, including a system for supplying transponders, comprising: at least one high-frequency transmitter that transmits a transmitted high-frequency output signal, and at least one high-frequency receiver that receives the transmitted high-frequency output signal, wherein the at least one high-frequency transmitter is connected to at least one antenna, and the at least one high frequency receiver is connected to at least one antenna, wherein the receiver obtains its operating power from the transmitted high-frequency output signal from said transmitter, wherein (1) the transmitted high-frequency output signal from the transmitter is modulated with at least one converter clock suitable for a DC-DC converter, (2) the receiver has at least one detector for demodulating the at least one converter clock from the transmitted high frequency output signal, (3) the receiver generates a DC operating voltage for the DC-DC converter from the high-frequency output signal using at least one of a rectifier and the at least one detector, (4) the DC-DC converter, using the at least one converter clock, and generating another DC voltage to operate further circuit elements, wherein one of an inductive switching controller and an inductive switching converter is used as the DC-DC converter, which by means of at least one electronic switch controlled by the converter clock, including a transistor, allows a switched current to flow through at least one inductance and thereby generate a high voltage at the at least one inductance during a disabling process, wherein the high voltage can be picked off directly using a fast switching diode, or decoupled via an additional inductance.

7. The device as claimed in claim 6, wherein a feedback pulse is generated at the inductance at the DC-DC converter to an input of the DC-DC converter.

8. The device as claimed in claim 1, wherein after initially generating an increased DC voltage to start up the circuit elements, converter clock generation is taken over locally in the receiver using the started circuit elements, including by one of local oscillators and by derivation from digitally encoded information of the transmitted signal, which makes it possible to use the radio frequency for data transmission purposes and further allows local load-dependent control of converter output voltage.

9. The device as claimed in claim 8, further comprising a reverse channel that communicates to the transmitter when the converter clock generation has been taken over in the receiver, which causes the transmitter to switch to a different operating state so that one of pulse modulation and amplitude modulation is replaced by one of a continuous transmitted signal (continuous wave) and a transmitted signal with a different pulse duty ratio.

10. The device as claimed in claim 1, further comprising specifically controlled semiconductor elements that cause impedance changes on at least one of an antenna of the receiver and at least one rectifier and detector of the receiver, which are used for feedback of digital information from the receiver to the transmitter, which is equipped with additional receiving components by changing a reflection and absorption behavior of a receiving antenna (backscatter modulation).

Description:

BACKGROUND OF THE INVENTION

The object of the invention is to transmit power from a transmitter to a receiver to enable operation of additional circuit elements or components on the receiver even if the receiver does not have any power supply of its own. Such a requirement exists, for instance, in transponders mounted to fast rotating parts, which thus elude a reliable external power supply and in which the use of batteries should be avoided for reasons of minimum maintenance. Such transponders are used, for instance, for electronic control of the tire pressure in motor vehicles as well as to identify moving goods, or as an item protection system to prevent shoplifting.

Prior art systems use inductive methods (near field) or radio waves with a constant carrier for power transmission. Such systems are described in detail, for instance, in the RFID-Handbuch [RFID Manual] by Klaus Finkenzeller, Hanser Verlag. The disadvantage of inductive systems is that the coils for generating and drawing the power require a lot of space and are heavy. In the radio systems, relatively high transmitting power is required to obtain a useable voltage at the detector due to the defined impedance of the electromagnetic field in free space of approx. 377 ohm (which results from the square root of the ratio of the physical constants mu 0 to epsilon 0 ) and the drop in the power density squared to the distance. The maximum permissible transmitting power, however, is usually limited due to government restrictions. Impedance conversion after the antenna is furthermore possible only within limits due to the losses that occur-particularly at the higher frequencies. On the other hand, the use of higher frequencies is desirable because of the smaller antenna size, the improved directional effect of the antennae, and the broader available frequency spectrum.

With the method described in Patent DE 19702768 by the same inventor it is already possible to query analog measured values over relatively long distances, a method that is also used for industrial applications. This method, however, is based on a purely analog circuit in the transponder, which requires a substantially lower operating voltage than comparable digital circuits.

It would be desirable, however, to obtain the higher operating voltage required to operate digital circuit elements as well. Since these circuit elements generally require very little current due to the use of CMOS technology, the object of the invention is to increase the provided voltage at the cost of the maximum available current while keeping the available output constant.

Such components are sufficiently known as voltage transformers, although the employed circuits again function only starting from a certain minimum voltage because the clock generators are otherwise not stimulated to oscillate. On the other hand, the radio frequency is typically not suitable as the clock frequency because it is much too high for this purpose.

SUMMARY OF THE INVENTION

The present invention relates to a device or system for wireless power transmission, particularly a system for supplying transponders, including at least one high-frequency transmitter and at least one high-frequency receiver, each of which is connected to at least one antenna, wherein the receiver obtains its operating power from the transmitted high-frequency output, wherein the high-frequency transmitter is modulated with at least one converter clock suitable for a DC-DC converter, the receiver has at least one detector for demodulating the converter clock, the receiver generates a DC operating voltage for at least one DC-DC converter from the high frequency using at least one rectifier or detector-which may also be identical with a detector for demodulating the converter clock, the DC-DC converter using the transmitted converter clock, and generating another DC voltage to operate further circuit elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of the Power Transmission System according to an embodiment of the present invention.

FIG. 2 shows a circuit diagram of the Power Transmission System according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the invention, a device or system for wireless power transmission, particularly for a system for supplying transponders, is described in detail below.

According to the invention, this problem is solved by the device set forth in claim 1 the function of which will now be described in detail.

The transmitter generates a pulse-modulated high-frequency signal. The pulse modulation frequency corresponds to the clock frequency of conventional DC-DC converters. The receiver now has at least one antenna-supplied rectifier with an energy storage element and a likewise supplied detector for the converter clock. Thus, two voltages are available: a continuous DC voltage at a low level and a square wave voltage. The latter now represents the clock for the DC-DC converter to increase the continuous DC voltage.

Such a power transmission system will now be described by way of example. In FIG. 1 the transmitted signal produced by generator G 1 of the transmitter SE 1 is pulse-modulated with frequency f 1 via circuit S 1 with frequency f 2 . This modulation frequency f 2 in turn is produced by a square wave generator G 2 . The transmitted signal is then emitted by antenna A 1 , possibly after additional amplification and filtering.

The receiver EM 1 now picks up the signal with antenna A 2 and supplies it to detector D 1 . At the output of this detector a DC voltage pulsed in time with the modulation frequency f 2 is available. In a particularly advantageous embodiment of the invention, the same signal is now used to provide the clock for the DC-DC converter W 1 on the one hand and its DC supply voltage on the other. This is accomplished in that the output signal of the detector is buffered by means of buffer capacitor C 1 , which is decoupled via a diode, so that sufficient power is available for the converter even during the pauses of the transmitted signal which are caused by pulse modulation.

To achieve better separation of the DC supply voltage from the clock, a band-pass or high-pass filter may be inserted in the path of the clock signal on the one hand and the DC supply voltage may be decoupled via an additional low-pass filter, particularly a reactor, on the other hand. This measure also reduces or prevents losses due to the switching times of the decoupling diode as well as undesirable negative feedback effects that may be created by a current consumption of the converter that depends on the converter clock.

In addition, the voltage level of the low frequency converter clock can be increased by impedance conversion. Besides transformers, particularly oscillating circuits tuned to the clock frequency with inductive or capacitive coupling or decoupling may also be used here. Through suitable circuit engineering measures, which are known as positive feedback, the signal level can be further increased.

If the quality of the clock signal is adequate as a result of the described filtering, the transmitter does not have to be completely disabled during pulse pauses, but merely transmits at reduced output, so that pulse modulation is replaced by amplitude modulation. Hence, in addition, energy is transmitted during pauses as well; on the other hand adjacent channel interference within the radio frequency spectrum is reduced.

The circuit of a receiver is depicted by way of example in FIG. 2 . The signal is picked up via the dipole as the receiving antenna, which comprises halves A 10 and A 11 , and is demodulated using a detector comprising capacitors C 100 to C 103 , diodes D 100 and D 101 , and resistor R 100 . The two diodes already double the voltage by using the peak-to-peak voltage of the received signal. C 100 advantageously provides DC voltage type decoupling of the antenna from the receiver mass. With R 100 as an additional load impedance, steeper clock signal edges, which are indispensable for proper efficiency of the converter, are achieved.

The output signal of the common detector is now converted into a minimally pulsating DC voltage by means of the buffer capacitor C 104 , which is decoupled with diode D 102 . This voltage is made available to the DC-DC converter.

When the high signal level of the converter clock is present, a steadily increasing current will flow through inductance L 100 , since the switching transistor V 100 , via the clock signal supplied by means of R 101 , is in its closed state. The buffer capacitor C 104 is thereby partially discharged. Ideally, at the proper time prior to the complete discharge of C 104 , the clock signal will change to the lower signal level, additionally supported by load impedance R 100 . The switching transistor then abruptly interrupts the current flow through inductance L 100 causing the latter to generate a high positive voltage pulse due to self-inductance at the common node with D 103 , which is further added to the remaining voltage of capacitor C 104 . This pulse is stored via diode D 103 in a further buffer capacitor C 105 . At this capacitor, the increased output voltage, which is required for instance to operate logic circuits, is now available.

The efficiency of the converter can be further enhanced by suitable feedback. Suitable, in particular, is feedback of the generated pulse, for instance via another winding of L 100 to the base of switching transistor V 100 .

It goes without saying that due to the high steepness of the pulse generated by inductance L 100 , the duration of the interruption of the transmitted signal can be kept very small due to pulse modulation, so that the transmitted power is enhanced. The square wave modulation signal used by the transmitter will have a high pulse duty ratio; this DC-DC converter type is therefore particularly well suited for power transmission according to the invention.

Of course, an integrated solution instead of the switching transistor is also feasible, as well as the theoretical use of semiconductor elements, for example, which at least on the voltages present at the detector or the buffer capacitor exhibit breakdown behavior (Z diodes).

In addition, to ensure a faster start of the converter, the frequency and pulse width of the clock signal can also be adapted dynamically by the transmitter. In particular, a pure carrier signal can initially be emitted for first-time charging of the buffer capacitor. When the required operating voltage is reached, feedback of load information to the transmitter is also feasible if a suitable reverse channel is available for this purpose.

In a further particularly advantageous embodiment of the invention it is also possible, after reaching the operating voltage necessary for logic circuits, to generate the further converter clock locally in the receiver and thus to control the converter output voltage, too, as a function of load. This switch may be communicated to the transmitter via a reverse channel, e.g., by a command in a digital data stream, so that the transmitter can be switched from pulsed operation to continuous operation to transmit additional power to the receiver.

For operation of the reverse channel, specific control of the impedance at the antenna is particularly suitable, which leads to a changed reflection behavior of the antenna and can be detected by the transmitter by means of additional receiving components (directional coupler in the antenna signal path and synchronous receiver connected thereto) in the manner of a radar object that changes its size. In the literature this type of retransmission of digital data sequences is also known as backscatter modulation. Advantageously, the request for continuous operation is synchronized with pulse modulation to obtain an optimal range of the reverse channel. Alternatively, the clock of the pulse modulation can also be used as a data clock or computer clock and only the pulse duty ratio further increased after switching.

This reverse channel can be simultaneously used for feedback, e.g., of measured values or identification codes. This creates a complete transponder system, to which this invention imparts a significantly greater range at reduced transmitter power and which in addition is extremely long-lived and environmentally friendly because it avoids the use of batteries.