However, we do not want a constant frequency oscillator. We want a siren. So to generate an up and down tone signal, the resistor R2 is fed from an RC circuit. When the switch S1 is pressed, the capacitor C1 charges through R1 slowly until it reaches the maximum voltage level of 4 volts. This increase results in a decrease of the voltage of the time constant at the junction R2/C2. This also results in an increase in the frequency of the multivibrator.

After the S1 is released, the capacitor C1 discharges slowly, resulting in a cycle of decreasing frequency. Through the combination of the two time constants a form of sawtooth wave is generated.The signal heard from the speaker will be a tone increase or decrease depending on whether the switch S1 is pressed or released.

Source : electroschematics.com

There are a number of input (hours, minutes, days, months, years, etc …) To perform the calibration and alarm clock also has a power-saving features that can be activated / deactivated by a switch and make the pic to disable the LCD power saving. We have a choice of 24h-12h.

In case of UJT, Vp is constant in device according to the dc supply voltage, but may differ in PUT to modify by changing the value of the resistor divider R1 and R2. If the anode voltage VA is smaller than the gate voltage VG, the device remains in an inactive state, but if the anode voltage exceeds the gate in a voltage drop of the diode VD, it will reach its peak and the device is activated.

The peak current Ip and Iv valley point currents of depends on equivalent impedance at the gate RG = R1R2 / (R1 + R2) and the dc supply voltage Vs. N generally Rk limited to values below 100 W. R and C controls the frequency with R1 and R2. Period of oscillation T is given around by :

T = 1/f = RC lnVs/Vs-Vp = RC ln (1+R2/R1)

Accordingly it seems that all displays will have to start with the same number, but it is not because the PIC is turning each display one at a time and the number that corresponds very quickly, so that we feel that all the displays are lighted simultaneously. This is a very common practice and is very useful to save wiring and PIC pin, imagine the amount of pins you would have if we handle all segments of all displays separately…

Here is the digital alarm clock circuit diagram : Although in this digital alarm clock scheme does not appear, the Integrated 7448 should be given a 5V supply, pin 16 to 5V and ground pin 8.

Instructions:

• When you install an alarm will display a flashing number. Tonbol Press 2 to change the hours and the 2 key to change minutes. When finished you can press 1 and displays stop flashing indicating that the time is set.
• To change the time at any time: press and hold button 3 for one second (approx.). Then press button 3 for the minutes and the 2 button for the hours. When finished press the 1 button.
• To change the alarm hold the 2 button for one second (approx.). Then press button 3 for the minutes and the 2 button for the hours. When finished press the 1 button.
• To view the alarm, press the 1 button, the alarm time is displayed for a few seconds.
• To enable or disable the alarm : Press the button. If the LED is lit the alarm will sound at the scheduled time, if off, the alarm no sound.
• When the alarm sounds: to stop permanently actuate the switch (switches off the LED). To make a delay press button 1, then the alarm will sound again after 5 minutes.

Source : electronica.webcindario.com

The reactance of a capacitor or a coil is the ohmic value which opposes the flow of electrons. When the frequency increases the reactance of the coil increases, while the capacitor decreases.

But there is a certain frequency, where the values ​​of the two reactor are absolute and equal, this phenomenon is called “resonant frequency”

Its value is deduced as follows:

XL = 2 * p * F * L XC = 1 = 2 * p * F * C

For the resonance frequency:

F = 1 = 2p L * C

The quality factor is something wider, can be defined in case of a coil, as the reaction:

Q = X_LR_L

Description:

To find the resonant frequency of the series resonant circuit, must be done by measuring the frequency sweep at the same time in voltage across R1, and to find the resonant frequency R1 should have a maximum voltage and in parallel resonant circuit must have a minimum voltage in R1.

When circuit perform resonance, both serial or parallel, the coil voltage is equal to the voltage of the capacitor, it means that the ohmic value fit (XL = XC.)

In the frequency calculations we realized that the value of different frequencies and apparently caused by (L) of the coil varies significantly from the theoretical to the practical.

There are coils different types according to their core and by type of winding. Its main application is as a filter in an electronic circuit

The Coil Characteristic

1. Magnetic permeability  -. Is a characteristic that has a great influence in core of the coil against the inductance value. Ferromagnetic materials are very sensitive to magnetic fields and produces high inductance values​​, but other materials are less sensitive to magnetic fields. Factors that determine the degree of sensitivity to the magnetic field is called the magnetic permeability. When this factor is large, as well as the value of inductance.

2. Quality factor (Q). – Relates inductance with the ohmic value of the bobbin. The coil will be good if the inductance is greater than the ohmic value due to the wire thereof.

TYPES OF COILS

A. FIXED COIL

Air core coil

The conductor is wound on a hollow support this being subsequently removed with an appearance similar to a spring. It is used at high frequencies. A variant of the above is called solenoid coil and differs in the insulation of the coils and the presence of a media that is not necessarily have to be cylindrical. Use when you need many turns. These coils may have middle tap, in this case can be considered as two or more coils wound on a support and connected in series. Also used for high frequencies.

Solid core

Inductance value is higher than previously because of their high magnetic permeability. Core of ferromagnetic material normally. The most commonly used is the ferrite and FERROXCUBE. When dealing with a large enough force to remove the low frequency using the same core in transformer (especially electricity). Part of the core can be in the form of EI, M, UI and L.

Honeycomb coils used in radio tuner circuits in the medium and long-wave range. Thanks to the form of high values ​​of the inductive coil is obtained in a minimum volume.
Toroidal coil is characterized by generated flow is not spread out because of its shape which creates a closed magnetic flux, giving them a good performance and accuracy.
Ferrite coil is wound on a ferrite core, usually cylindrical, with applications in radio is very interesting from a practical standpoint because it allows the assembly of the antenna works by placing it directly to the recipient.

The coils etched on copper, on a printed circuit have the advantage of its low cost but are difficult to set via core.

B. VARIABLE COIL

Adjustable coil is also produced. Usually variations in the inductance caused by core movement. Shielded coil can be fixed or variable, must attach a metal coil in a cylindrical or rectangular cover, whose duty is to limit the electromagnetic flux generated by the coil itself and the nearest component that can be harmful to it.

Capacitor voltage does not change immediately, and go from 0 volts to E volts (E is the direct current source connected in series with R and C, see Figure).

The time required for the capacitor voltage (Vc) to pass from 0 volts to 63.2% from the voltage source can be calculated by the formula Q = C x R where R is in ohms and C in Milifarads and tht results will be in milliseconds.

After 5 x T (5 times T) the voltage has increased to 99.3% from final value

Value of T is called the “time constant”

By analyzing the two graphs you can see that these is divided into transient zone and stable zones. The values ​​of Ic and vc have varying values ​​in transient zones(approximately 5 times the time constant T), but not in the stable zones.

Vc and Ic value each time can be obtained by the following formula:

Vc = E + ( Vo – E) x e^{-T/ t}  ,

Vo is the initial voltage of the capacitor (in many cases is 0 Volts)

Ic = ( E – Vo ) x e^{-T/ t}/ R

Vo is the initial voltage of the capacitor (in many cases is 0 Volts)

VR = E x e^{-T/ t} Where : T = R x C

Capacitor Discharge process :

The switch is at B.

Then the voltage Vc across the capacitor begins to descend from Vo (initial voltage across the capacitor). The current will have an initial value of Vo / R and decrease until reaching 0 (zero volts).

The values ​​of Vc and R at any time can be obtained with the following formulas:

Vc = Vo x e^{-t / T} I = -(Vo / R) e^{-t / T}

Where: T = RC is the time constant

NOTE: If the capacitor had been previously charged to a value E, replace Vo in formulas with E

In the CD4094 data are synchronized on the rising edge and the LCD display will take on the falling edge shows us that this signal can be shared.

Well, then at the rising edge CD4094 transfers the data of the new byte out and fall on the side of the LCD display reads. Keep in mind that this method can not read LCD information display.

Now comes the hard part: How to separate text commands. LCD has a pin for this: RS pin. When this command for 0 accepted, as accepted in a text (ASCII characters). How do you solve this?

Before sending a character to initialize a timer on CD4094 500uSec. The resistor R1 will load capacitor C5. Then send the character to the CD4094 as quickly as possible. Thus, the capacitor simply does not have enough time to discharge. The LCD display will accept it as text. In order to command is the same, only in reverse. The capacitor has to be discharge.

Emitter follower T1 formed to protect the network R / C. The reason for this is that the LCD RS input is a TTL input signal and we put it to work quite well.

Program C Language

#include <hidef.h>
#include "derivative.h"

#define LINE1    0x80
#define LINE2    0xC0

#define DTASHT   0x01     // PTA0
#define CLKSHT   0x02     // PTA1
#define STBSHT   0x04     // PTA2

#define CTRL     1
#define DATA     0

void Shift(char, char);
void Delay(int);
void Write(char, char*);
void Init_Dsp(void);

void main(void) {

CONFIG1 = 0x01;
CONFIG2 = 0x00;

DDRA    = 0x07;
PTA     = 0x00;

Init_Dsp();

for(;;) {
Init_Dsp();
Write(LINE1,"  Hola Mundo    ");
}
}

//=====================================

void Init_Dsp(void) {
PTA |= CLKSHT;
Shift(CTRL,0x06);
Shift(CTRL,0x0E);
Shift(CTRL,0x38);
Shift(CTRL,0x80);
Shift(CTRL,0x0C);     // Cursor off
Shift(CTRL,0x01);     // Clear Display
}

void Write(char pos, char *text) {
Shift(CTRL,pos);
while(*text) Shift(DATA,*text++);
}

void Shift(char donde, char dato) {
int i;

for(i=0; i<8; i++){
if(dato & 0x80) PTA |=  DTASHT;
else            PTA &= ~DTASHT;

if(donde) {
PTA &= ~CLKSHT;
Delay(200);
PTA |=  CLKSHT;
}
else {
PTA &= ~CLKSHT;
PTA |=  CLKSHT;
}
dato <<= 1;
}
PTA |=  STBSHT;
PTA &= ~STBSHT;
if(donde) Delay(2000);
}

void Delay(int time) {
for(; time>0; time--);
}

As seen in the IR Wireless Headphone schematic, transmitter circuit is very simple here. The transformer assembled as a matching impedance, and low impedance windings are connected in parallel with the TV or radio speaker. IR diodes are commonly used. 10 ohm resistor that limits the current through the IR diode should be 1 mg. This 9Vdc powered transmitter that can be provided either by regular batteries or AC / DC adapter.

As the receiver is concerned, the same infrared light captured by the phototransistor, it is pre-amplified and amplified by transistors BC549C and then gives enough power to move the speaker of headset through the output transistor.

This receiver, like the transmitter is also powered from 9Vdc, but in this case must inevitably be provided by the battery, because with AC / DC adapter all this will be useless. Would look funny, right? When we use a wireless Headphone. But still use power supply with cable.

Remember that the audio is transmitted must have line of sight between the transmitter and receiver.

You can extend the range of the transmitter by placing more transistors BD140 with more IR LEDs.

The unit of density in the International System of Units is tesla.

Is given by:

where B is the magnetic flux density generated by a load moving with velocity v at a distance r from the load, and ur is the unit vector connecting the load to the point where B is measured (point g).

or :

where B is the magnetic flux density generated by a conductor through which flows a current I, at a distance r.

The formula of this definition is called the Biot-Savart, and magnetism is equivalent to Coulomb’s law of electrostatics, as used to calculate the forces acting on moving charges.

The field induction, B, or magnetic flux density (the three names are equivalent) is essential in the field H electromagnetism, since it is responsible for the forces on the moving charges and is, therefore, the physical equivalent to E.