Circuit Wiring

Multivibrator is a relaxation oscillator type. This circuit uses the RC network and the region contribute to the square wave output. Astabel multivibrator used in the TV receiver to control the electron beam on the picture tube. In this series of computers used to develop the pulse time.

A multibrator consists of two cross-coupled amplifier. The amplifier output is one connected to another amplifier wedding. Because each penguata reverse input signal, the combined effect of this is in the form of positive feedback. With the feedback posotif, the oscillator will always get the extra energy (regenerative) and produces a continuous output.

The picture above shows the multivibrator circuit using 2 pieces of bipolar transistors with common emitter configuration. R1 and R2 provide bias voltage developed at the base of each transistor. Holding capacitor C1 to the base collector Q1 Q2. Q2 together with capacitor C2 to the base of Q1.

Because of this cross coupling, a transistor will be conductive and the other is the cutoff. The two transistors alternately will live and die so that the outputs are labeled Q or. That output has a polarity reversal.

When the power given to the multivibrator, one transistor will berkonduksi first, let us assume here that berkonduksi Q1 first. With Q1 berkonduksi voltage on R and Vc decreased, so that its value is lower than VCC. As a result akn happened to the negative voltage on C1 and the positive base voltage of Q1 will decrease. Q2 conduction is reduced and the collector voltage equal to VCC. Voltage will be towards the positive on the C2. This voltage is added to the base of Q1 and make it more berkonduksi. This process continues until reaching saturation point Q1 and Q2 to reach the cutoff.

Multivibrator device functioned as a trigger (triggered device) or free-running. Multivibrator trigger requires the input signal / pulse. Multivibrator output is controlled or synchronized by the input signal.

When the output voltage of each transistor achieve stability, then there is no voltage feedback. Q2 will return berpanjar forward through R2. Conduction in Q2 will lead to a decrease in VC. Voltage to the negative direction will be given on the basis of Q1 through C2. Q1 conduction is reduced. Vc in Q1 will rise worth with Vcc. This will tergandeng to the base of Q2 through C1. This process continues until Q2 Q1 reached saturation point and reach the cutoff. The output voltage then becomes unstable and the process will be repeated.

The frequency of oscillation of the multivibrator time constant distentukan by R2 and R3 and C1 and C2. The R2 and R3 are chosen such that each transistor can reach saturation point. C1 and C2 is selected to obtain the desired operating frequency. If C1 = C2 and R2 = R3 then the output will be symmetrical. Means that both transistors will live and die in selag the same time.

One type of metal detector is a type of beat frequency oscillator (BFO). The methods used in metal detectors in general are changing the characteristics of the oscillator when there are close to the metal sensor. The detector works based on the resonant frequency that has been set change when there is a metal object is located quite close to the search coil sensors.


Tuning circuit (tuned circuit) should be a part of our oscillator circuit so that if approached by a metal coil sensor specific hence the output frequency of the oscillation circuit is about to change. Variation changes the output frequency depends on the frequency chosen. The selection of the higher frequency will cause the circuit sensitivity increases because the greater the frequency change. Stay if the selection frequency is too high then the practice will produce a system that is not sensitive. This is because the high frequency of most will not be reflected back but will be absorbed by the soil, building materials.

Frequency used (f1-produced by the tank circuit with L1) is usually above the human hearing ability. Because it can not be heard by human pendegaran the frequency changes that occur will also not be heard as well. To overcome this it should be made a separate tone (audible frekuency-f2) which shows the change in frequency. This is said with the beat.

By mixing the two signals (f1 and f2) will produce signals f1, f2, (f1 + f2), and (f1-f2). The signal can be heard by human hearing is a signal (f1-f2). So when there are changes in frequency caused by changes in the characteristics of the search coil can be heard by humans as a rhythm-beat changing. Rhythm-beat is what is the signal (f1-f2) earlier.

VC1 setting is not easy because it requires experiments on certain metals. Similarly, for setting the rhythm of the beat is heard because at a certain condition will feel the rhythm of this beat very disturbing. So it was no possibility the beat or rhythm is not produced beatnya lower than normal because all these conditions can be set on VC1.

So when there are changes in the characteristics of the search coil it will produce sound frequency also depends on the different frequencies generated by the L1 and L2 frequencies generated by.

This method still has the disadvantage that its output frequency variation is still too small to change its frequency is almost not visible. Additionally, on certain conditions Dapa produce a frequency below the audible sound. For that we need a reconfiguration of coupling capacitors and the frequency of use.

The values ​​of existing components dirangkaian Figure 2 represents the values ​​specified in a metal. So for a specific metal component values ​​need to be adjusted especially VC1, C1, C4, and C5.

Inductor L1 is formed from the coil that serves as a search coil. This inductor will resonate along with the VC1 to produce a tank circuit with Q high. The second oscillator is formed from L2, C4, C5, R4, and Q2 and the oscillator circuit will produce a signal with a fixed frequency. D1 serves as a simple mixing between f1 and f2 and will generate a signal with a frequency (f1-f2) and a lot of harmonic signals. Signal with a frequency (f1-f2) is made so that it can be in areas that can be heard by human hearing.

Suppose that f1 and f2 on the 100KHz 101KHz then after dimixer, signal (f1-f2) will produce a signal with a frequency of 1kHz. This differential signal must be amplified in advance using a opamp that will only be able to drive headphones with high impedance. If the chill to be used for regular headphones then Dapa LM741 amplifier chip is replaced with the type of audio amplifiers. Because ampilifier audio output has a low impedance. Amplifier gain setting is determined from the setting R7 and R10, and if necessary the output of the LM741 can be incorporated into a power amplifier circuit to drive an spaker.

Circuit in Figure 2 is very simple to allow the occurrence of frequency drift - a shift in frequency. This is usually caused by the temperature factor. However this problem is not a serious problem. Permsalahan can ditanganni by searching for capacitor components which have a large enough temperature tolerance. In addition, PCB layout also has a huge effect on this problem.

The size of the search coil depends on the sensitivity of metal detectors are cooled and form of the sensor itself. For example, a large search coil which of course can easily find the metal you are looking at a large area rather than a metal detector with a small search coil. Instead of metal detectors can not determine the location of cables on a wall tertanan precisely because of the large size of the sensor.

So the greater the search coil, the accuracy of his smaller but bigger sensitivty but instead a small search coil, commonly used to compact metal detector, have high accuracy but less sensitivity. The shape of the search coil is usually a circle or square. Besides needing a shield layer which serves to reduce electrostatic effects and effects caused by capacitive objects.

Toggle switch in this article is a series of toggle switches that are controlled by infrared light. The series toggle switch is made from a combination of data flip-flop CD4013 2 units. Receiver circuit of the infrared light signals arranged with infrared receiver as found on television remote receiver. Infrared signal from remote is used as clock signals and data to the data flip-flop first. then the second flip-flop data set as a toggle flip-flop toggle the output signal is used to drive the relay. for more details can be seen in thethe following image .

Series Toggle Switch With Infra Red (IR) that is required to supply voltage range of 12VDC and the output of Toggle Switch With Infra Red (IR) is dapt used to turn on the lights or other electronic devices with DC or AC voltage source. Series Toggle Switch With Infra Red (IR) was isolated from the load that is placed for use as the final relay.

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In ADC 0804 interface techniques with microcontrollers are pin-pin control must be controlled if we want to use the ADC with the microcontroller, there is value addition refferensi voltage to be supplied in 0804 ADC interface with a microcontroller, for example, we use the 0804 ADC (8 bit), if we give refferensi voltage 2.55 volts then we will get the increase of 1 bit to change 10 mVolt. Please note that the 0804 ADC pin on the leg that is form Vref Vref / 2, so to get a 10mV resolution is necessary for setting Vref / 2 equal to 1.275 V

The interface circuit microcontroller with ADC 0804

Mechanical interface microcontroller with ADC 0804

The steps in accessing data from the ADC 0804 by the microcontroller sebgai follows;

Enable ADC with signal 0 at the foot of Chip Select.

Give commands from conversion by providing a low pulse to the foot of the ADC Write narrow

Wait for the ADC issued a signal 0 from his leg INT

Give a moment of time delay for data from the ADC is correct

Give the read command by giving the signal 0 at the foot of ADC Read

Give a moment of time delay

Now data from the ADC is ready for use and if the microcontroller.

Anyone who uses this amplifier circuit would be surprised. Although this circuit has a small power output just 10 watts , but also issued a sound loud enough. At least match the transistor power amplifier with 60 watts. And his sound is good with low noise. Minimum voltage is 2 volt , and maximum voltage is 12 volt .

Schematic circuit power amplifier AN7117 below :