Sound-Activated Switch using Op amp 741

          Sound activated switch shows how to make an adjustable reference voltage of 0 to 100V. We use a 10 kΩ pot, 5 kΩ resistor, and +15V supply to generate a convenient large adjustable voltage of 0 to 10V. Next we connect a 100:1 voltage divider that divides the 0 to 10V adjustment down to the desired 0 to 100mV adjustment reference voltage. Again, signal source E_i is used as a microphone and an alarm circuit is connected to the output.

          With this sound-activated switch, control by sound may be very useful in different ways. For example, a sound-activated light responding to a knock on the door or a hand clap. The light will be automatically switched off after a few seconds. Actually, the practical application that uses a positive level detector is the sound-activated switch shown in Figure.

          Any noise signal will generate an ac voltage and microphone is used as an input. The first positive swing of Op amp of E_i above V_ref drives V_o to +V_sat. The diode now conducts a current pulse of 1 mA into the gate, G, of the silicon-controlled rectifier (SCR). Normally, the SCR’s anode, A, and cathode, K, terminals act like an open switch.

Fig: A sound-activated switch is made by connecting the output of a non-inverting voltage-level detector to an alarm circuit.

However, the gate current pulse makes the SCR turn on, and now the anode and cathode terminals act like a closed switch. The audible or visual alarm is now activated. Furthermore, the alarm stays on because once SCR has been turned on, it stays on until its anode-cathode circuit is opened.

            The circuit of Figure can be modified to photograph high-speed events such as a bullet penetrating a glass bulb. Some cameras have mechanical switch contacts that close to activate a stroboscopic flash. To build this sound-activated flash circuit, remove the alarm and connect anode and cathode terminals to the strobe input in place of the camera switch. If we open the camera shutter and fire the rifle at the glass bulb, the rifle’s sound will activate the switch.

        The strobe does the work of apparently stopping the bullet in midair. If we close the shutter, the position of the bullet in relation to the bulb in the picture will adjusted experimentally by moving the microphone closer to or farther from the rifle.

           We use sound activated switch circuit in different ways. For light activated relay switches, machine gun sounds, sound activated FM transmitter, sound effects generator electronic circuit, auction of test equipment and many other works we use this circuit. This sound activated switch circuit makes our activities easy and comfortable.

Smoke Detector

           Small change of light the smoke detector will be activating. Initially photo-conductor resistance shall have to high value. Total Circuit designing. Smoke Detector is a detector which is activating by the smoke. It is another practical application of a voltage-level detector. Smoke Detector is working with the change of voltage. This circuit can be used in fire alarm.

          Smoke Detector of Figure the lamp and photo-conductive cell are in an enclosed chamber that admits smoke or dust but not external light. The photo-conductor is a light-sensitive resistor. In the absence of smoke or dust, very little strikes the photo-conductor and its resistance stays at some high value, typically several hundred kilohms. The 10-kΩ sensitivity control is adjusted until the alarm turns off.

          Any particles entering the chamber cause light to reflect off the particles and strike the photo-conductor. This, in turn, causes the photo-conductor resistance to decrease and the voltage across R1 to increase. As E_i increases above V_ref, V_o switches from –V_sat to +V_sat, causing the alarm to sound. 

           In initial condition photoconductor resistance must contain high resistance otherwise the detector will be always activated. When the voltage of inverting terminal and non-inverting terminal are same output show 0 V. 

           Output voltages not more then supply voltage. The resistive network at the input of the op-amp forms a Wheatstone bridge. This circuit can be used to monitor the level of dust particles in a clean room.

Integrator Circuit Using Op amp 741

            An integrator is a circuit which shows the sum of input voltage at the output. That means it works by the operation of integral form. If we see the output of the integrator shows the summation of input voltages, the result of integrator circuit will be right. Such that, if we give square wave at the input, then we will get triangular wave at the output.

             A circuit in which the output voltage waveform of Op amp is the integral of the input voltage waveform is the integrator or the integrator amplifier. Such a circuit is obtained by using a basic inverting amplifier configuration if the feedback resistor R_F is replaced by a capacitor C_F.

        Integrators are used in the design of signal generators and signal processing circuits. It is also used in analog computers and analog-to-digital (ADC) and signal-wave shaping circuits.

              When V_in = 0, the integrator of Fig 1(a) works as an open-loop amplifier. This is because the capacitor C_F acts as an open circuit (X_CF = ∞) to the input offset voltage V_io. In other words, the input offset voltage V_io and the part of the input current charging capacitor C_F produce the error voltage at the output of the integrator.

         Therefore, in the practical integrator to reduce the error voltage at the output, a resistor R_F is connected across the feedback capacitor C_F. Thus, R_F limits the low-frequency gain and hence minimizes the variations in the output voltage.

        Both the stability and the low-frequency roll-off problems can be created in ideal integrator. Those problems can be corrected by the addition of a resistor R_F. From the simulation result, we can see that the output of square wave is the triangular wave. So, we can say that integrator does the sum at the output.

Design a Subtractor

         A basic differential amplifier can be used as a sub-tractor. We can get the difference of two input voltages in the output of op-amp as output voltage. The circuit diagram of a basic differential amplifier is drawn below.

         This is a linear bilateral network. So, applying super position theorem, we can find the output voltage equation.

Let, assume that only Va is applied and Vb is short.

Voltage to current converter with floating load

          The current in the feedback loop depends on the voltage and Ri. This applications where we need to pass a constant current through a load and hold it constant despite any changes in load resistance or load voltage. When the load does not have to be grounded, we simply place the load in the feedback loop and control both input and load current  from this circuit.

          

This circuit shown in figure voltage to current converter with floating load. The voltage to current converter can be used in such applications as low voltage dc and a voltmeters, diode match finders light emitting diodes (LEDS) and zener diode tester.

         This circuit diagram Figure shows a voltage to current converter in which load resistor R_L is floating (not connected to ground). The input voltage is applied to the no inverting input terminal and the feedback voltage cross R₁ drives the inverting input terminal. This circuit is also called a current series negative feedback amplifier because the feedback voltage across R­₁ (applied to the inverting terminal) depends on the output current i₀ and is in series with the input difference voltage v_id.

First Order Low Pass Filter

Here an explanation of the operation of low pass filter was made, the operation principle of active low pass filter was made, of active low pass filter was made, I designed an active low pass filter & finally I have drawn the frequency response of designed active filter by using filter gain equation & plotting the frequency vs. gain curve. 

An electric filter is frequency-selective circuit that passes a specified band of frequencies & blocks or attenuates signals of frequencies outside this band. Active filters can be designed using op-amps, resistors, capacitors or inductors. RC filters are used for audio or low frequency operation, where LC filters are used for high frequencies. For designing audio filters I used capacitors, because inductors are very large, costly & may dissipate more power. I chose active filters instead of passive filters because,

a.        It has gain & frequency adjustment flexibility.

b.       It has no loading problem.

c.        It has very high input impedance & very low output impedance.

d.       It is more economical than passive filters.

I designed first order low pass butter-worth filter with RC network in my present assignment. The key characteristic of butter-worth filter is it has a flat pass-band & a flat stop-band. The ideal and practical frequency response of a first order low pass filter is given below,

           

The above figure shows the frequency response of a 1^st order low pass butter-worth filter. The ideal frequency response is shown by the dashes line while the practical response is shown by the solid line. We can see from the frequency response that, the filter allow signal with frequencies less than f_H to pass through it & the signal appears at the output with predefined gain.

Ideally it attenuates the signal appearing at the input which has frequencies greater than f_H & gives zero output. Ideally at f_H, the frequency response curve changes sharply from A_F (closed loop gain) to zero.  Hence the frequencies from f to f_H are called pass-band frequencies & frequencies greater than f_H are called stop-band frequencies.

f_H is called high cutoff frequency. Unfortunately the change is not so sharp at f_H in practical low pass filters. In practical 1^st order low pass butter-worth filter gain changes with 20dB/decade with frequencies greater than f_H.

Third-Order High-Pass Filter

       This report focuses on active third-order high-pass filter design using operational amplifiers. High-pass filters are commonly used to implement high frequency in a system. Design of Third-order filters is the main topic of consideration. To illustrate an actual circuit implementation, separated into two types of filters first-order and second-order.

       A third-order high pass filter is formed by connecting in series first and second order high pass section and so on. As the order of the filter increased, the actual stop-band response of the filter approaches its ideal stop-band characteristic. The overall gain of the filter is fixed because all the frequency determining resistors and capacitor are equal.

         A filter is a device that passes electric signals at certain frequencies or frequency ranges while preventing the passage of others. High Pass Filter (HPF), sometimes called a low-cut filter, is a filter that high frequencies can be transmitted well and frequencies lower than the cutoff frequency are attenuated or reduced.  The actual amount of attenuation for a particular frequency varies from filter to filter.

        A third-order high pass filter is formed by connecting in series first and second order high pass section and so on. In the stop-band the gain of the filter changes at the rate of 20 dB/decade for first-order filter and at 40 dB/decade for second-order filter. This means that, as the order of the filter is increased, the actual stop-band response of the filter approaches its ideal stop band characteristic.

         Higher order filter are formed simply by using the first and second order filter. A third-order high pass filter is formed by connecting in series first and second order high pass section and so on. Although there is no limit to the order of the filter that can be formed, as the order of the filter increase, so does its size.

         Also, its accuracy declines, in that the difference between the actual stop-band response and the theoretical stop-band response increase with an increase in the order of the filter.  Note that in the third order filter the voltage gain of the first order section is one, and that of the second order section is two. This gain values are necessary to guarantee butter-worth response and must remain the same regardless of the filter’s cutoff frequency. Furthermore, the overall gain of the filter is fixed because all the frequency determining resistors and capacitor are equal.

 

             Generally, the minimum-order filter required depends on the application specifications.     Although a higher-order filter than necessary gives a better stop-band response, the higher-order type filter is more complex, occupies more space, and is more expensive. As the order of the filter increased, the actual stop-band response of the filter approaches its ideal stop-band characteristic.

555 Timer Modeling

The 555 IC timer chip is widely used as both a monostable and astable multivibrator. Originally introduced by Signetics using bipolar technology, the 555 is now available from several manufacturers in bipolar and CMOS technology.

First-Order Band-Pass Filter

          Application of first order band pass filter to find out the output voltage gain magnitude of specific frequency. A specific range of frequency can pass through the amplifier which has a specific bandwidth of this band pass filter.

A band pass filter is a frequency selector. It allows one to select or pass only one particular band of frequencies from all other frequencies that may be present in a circuit. This type of filter has a maximum gain at a resonant frequency.

A band pass filter is the combination of high pass and low pass filter combination. It has a pass band between two cut off frequency f_H and f_L such that f_H > f_L. Any input frequency outside this pass band is attenuated. There are two types of band pass filters wide band pass and narrow band pass. If the quality factor Q < 10 and Q > 10 then it would be wide band pass and narrow band pass filter.

          The relationship between Q, the 3-dB bandwidth and the center frequency f_c is given by,

             
       According to Figure 01 of band pass filter circuit, there are two sections. One is first order high pass section and other is low pass section.

 For first order high pass section the output voltage equation is,

For first order low pass section the output voltage equation is,

Putting the value of first order high pass section output voltage  from equation (1),

So the final voltage equation of first order band pass filter is,

        
         The voltage gain magnitude of the band pass filter is equal to the product of the voltage gain magnitudes of the high pass and low pass filters.

Therefore the equation (2) is,

Where,  = Total band pass gain

f = frequency of the input signal (Hz)

 = low cut off frequency (Hz)

= high cut off frequency (Hz)

The above first order low pass band width filter was designed by taking following precautions,

a.       
 Limited magnitude of input voltage was applied at the input, so that the op-amp must not be driven to saturation.

b.                 Only selected frequency can pass through the filter.

c.                         Overall gain of the first order band pass filter is the multiplication of  high pass filter gain and low pass filter gain.

Electric Analog Computation

               Electronic analog computation is one of the basic concepts in the field of modern electronic computing. In electronic analog computation any equation  can be solved by using some analog circuits which is designed by using op-amps .In my assignment I try to present the concept of electronic analog computation by solving a differential equation with a correspondent circuit .

        Electronic analog computation is such kind of electronic computation in which basic analog computing elements such as adders ,integrators ,multipliers, comparators etc are used to solve any desired equation such as differential equations etc .It is the basic concepts of analog computer.

            In this a differential equation is solved by electronic analog computation.

                   Let a differential equation be :

                                          

 D²v+k₁Dv+k₂v-v₁=0……………….(1)   Where, k₁ and k₂ are constant terms.

           In the starting I assumed that D²v is available in the form of a voltage .Then by means of an integrator I will get  the voltage proportional to Dv. A second integrator gives the voltage proportional to v .Then an adder gives –( k₁Dv+k₂v-v₁)  From the equation it is equal to D²v

and hence the output of this summing amplifier is fed to the input terminal ,where I had assumed that D²v was available in the first place.

       The integrator 1 has a time constant RC=1s, and hence its output at terminal 1 is –Dv .This voltage is fed to a similar integrator 2 and the voltage at terminal 2 is +v. The voltage at terminal 1 is fed to summing amplifier 1 which gain is 1 and in the output terminal 3 I get + k₁Dv- v_1.

         where k₁=(R/R₁).At the end the output of terminal 2 and 3 are fed to summing amplifier 2,from where I will get  D²v= - (k₁Dv+k₂v-v₁) at terminal 4.

 

Fig1.1: Electronic analog computing circuit for calculating a differential equation .

              By electronic analog computation we can solve any kind of equation by some basics circuits using op-amp .But we have to careful to set the gain of the circuits because in some steps the constant term of the equation is  represent by the gain of the correspondent circuit .So, we have to design the circuits according to gain which represents the constant term

Design a Temperature Indicator

This circuit is a temperature indicator circuit or differential instrumentation amplifier using a transducer bridge. This circuit is calibrate in degrees Celsius or Fahrenheit. In the circuit used buffer in  and  points for exact voltage of  and  points. Because gain is always 1 of buffer circuit. Then the output voltage of buffers is input voltage of differential amplifier. 

The differential amplifier is difference voltage of  and  points using 741 Op Amp. When temperature is increased then resistance  is also decreased and output voltage  is decreases and when temperature is decreased then resistance  is also increased and output voltage  is increases.

The temperature indicator is a circuit that indicates of temperature in degrees Celsius or Fahrenheit. The temperature is inversely proportional to the resistance or transducer.

  The Fig.01 simplified a temperature indicator circuit using a transducer bridge. A restive transducer whose resistance changes as a function of some physical energy or temperature is connected in one arm of the bridge with a small circle around it and is denoted by , where  is the resistance of the transducer and  is the change in resistance.

Fig.01 - Temperature indicator

In the circuit used as the transducer in the bridge circuit is a thermistor and replaced output voltmeter to temperature indicating meter. Then temperature indicating meter is calibrate in degrees Celsius or Fahrenheit. 

The bridge can be balanced at a desired reference condition, for instance 25⁰C. As the temperature varies from its reference value, the resistance of the thermistor changes and the bridge become unbalanced. This unbalance bridge in turn produces the meter movement.

Analog weight Scale

The most common weight-scale implementation is to use a  transducer bridge, with voltage output directly proportional to the weight placed on it. The trend in weight scales towards higher accuracy and lower cost has produced an increased demand for high-performance analog signal processing at low cost.By connecting a strain Gage in the bridge ,the differential instrumentation amplifier can be converted in to a simple analog weight scale.

 In the analog weight scale, strain Gage elements are connected in all four arms of the bridge. The elements are mounted on the base of the weight platform, so that, when an external force or weight is applied to the platform, one pair of elements in the opposite arms elongates, whereas the other pair of elements in the opposite arms compresses.

 On the other hand, When no weight is placed on the platform, the bridge is unbalanced, R_T1=R_T2=R_T3=R_T4=R, and the output voltage of the weight scale can be zero. When a weight is placed on the scale platform, the bridge becomes unbalanced. In other words, when the weight is placed on the platform, R_T1 and R_T3 both decrease in resistance and R_T2 and R_T4 both increase in resistance (Figure 01).

 

The analog weighing measuring scales need to be hung properly before we start measuring anything using the same. They never allow measuring the weight of anything that we want as they have some limitations. If we think about measuring anything using an analog scale we need to check the analog lines to get the nearby accurate measurement.


One thing we need to keep in our mind while using such a scale is the limitation, if we load anything which weights more than the mentioned limit by the manufacturer of the scale we may end up damaging the same. Analog scales were never capable of providing accurate weight of any item and at the same time, it involves human effort to measure anything where the chances of human error are quite normal

For better accuracy, a microprocessor-based digital weight scale may be constructed.But it is much more complex and expensive than the analog scale.

The Differential Input and Differential Output

For getting balanced differential output  we use this circuit. In this circuit  two source is present, so the superposition theory is applied to get the output. In this circuit both the inverting and non-inverting terminal is working.It rejects the common-mode voltages, so  it is very useful in noisy environments.

A  differential input and differential output amplifier using two identical Op amp. It is     most commonly used as a preamplifier and driving push-pull  arrangement. The differential input and output  are inphase or the same polarity provided  V_in  =V_x – V_y and

V_o  =V_ox – V_oy

When we want to find out the 1^st op-amps output V_OX , we will use the  superposition theory.

When we get  V_X  is active , V_Y  is  inactive then ,

In non inverting terminal 

V₁= (1+ )V_X

When we get  V_y   is  active,  V_x   is  inactive then,

In  inverting terminal,

V₁ = - V_y

 So, V_ox = V₁+V₁

                =(1+ )V_X  -  V_y

 

Fig: The circuit diagram of the differential input and output amplifier. 

When we want to find out the 2^nd  op-amps output V_Oy ,we will use superposition theory.

                      When we get  V_X  is active , V_Y  is  inactive then

                      In  inverting terminal ,

                      V₂= - V_x

        

      Again, when  we get  V_y  is  active ,  V_x  is  inactive then

        In non inverting terminal we get, 

V₂= (1+ )V_y

So, V_oy = V₂+V₂

                                      =(1+ )V_y - V_x

So the output result   

V_o = V_ox  –  V_oy 

= (1+ )V_X  -  V_y  –[(1+ )V_y - V_x ]

                                      = (1+ ) ( V_X - V_y ) +( V_X - V_y )

                                       = ( V_X - V_y ) (1+ )

Design

To design a input and differential output amplifier,  taking a  differential output of at least 3.7V and the  differential  input V_in  =10V.

                        We know,

 V_o = ( V_X - V_y ) (1+ )

            Or, 3.7 = (0.1) (1+ )

 Or, 37 = (1+ )

            Or, 36 = 

            Or, R_f  = 18 R₁

                                    Let, R₁ = 100Ώ, then R_f  = 1.8 KΏ . 

                   Fig: The designing circuit diagram of the differential input and output amplifier.