AT89C2051 Digital Visitor Counter Circuit

AT89C2051 Digital Visitor Counter Circuit

Digital visitor counter is a reliable circuit that takes over the task of counting Number of Persons/ Visitors in the Room very Accurately. When somebody enters into the Room then the Counter is Incremented by one and when any one leaves the room then the Counter is Decremented by One. The total number of Persons inside the Room is displayed on the seven segment displays. The microcontroller do the above job it receives the signals from the sensors, and this signals operated under the control of software which is stored in ROM

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Automatic Railway Gate Control & Track Switching

Present project is designed using 8051 microcontroller to avoid railway accidents happening at unattended railway gates, if implemented in spirit. This project utilizes two powerful IR transmitters and two receivers; one pair of transmitter and receiver is fixed at up side (from where the train comes) at a level higher than a human being in exact alignment and similarly the other pair is fixed at down side of the train direction. Sensor activation time is so adjusted by calculating the time taken at a certain speed to cross at least one compartment of standard minimum size of the Indian railway. We have considered 5 seconds for this project. Sensors are fixed at 1km on both sides of the gate. We call the sensor along the train direction as ‘foreside sensor’ and the other as ‘aft side sensor’. When foreside receiver gets activated, the gate motor is turned on in one direction and the gate is closed and stays closed until the train crosses the gate and reaches aft side sensors. When aft side receiver gets activated motor turns in opposite direction and gate opens and motor stops. Buzzer will immediately sound at the fore side receiver activation and gate will close after 5 seconds, so giving time to drivers to clear gate area in order to avoid trapping between the gates and stop sound after the train has crossed.

The same principle is applied for track switching. Considering a situation wherein an express train and a local train are traveling in opposite directions on the same track; the express train is allowed to travel on the same track and the local train has to switch on to the other track. Two sensors are placed at the either sides of the junction where the track switches. If there’s a train approaching from the other side, then another sensor placed along that direction gets activated and will send an interrupt to the controller. The interrupt service routine switches the track. Indicator lights have been provided to avoid collisions. Here the switching operation is performed using a stepper motor. Assuming that within a certain delay, the train has passed the track is switched back to its original position, allowing the first train to pass without any interruption. This concept of track switching can be applied at 1km distance from the stations.

The project is simple to implement and subject to further improvement.

Model of Automatic Railway Gate Control & Track Switching

Gate Control:

Railways being the cheapest mode of transportation are preferred over all the other means .When we go through the daily newspapers we come across many railway accidents occurring at unmanned railway crossings. This is mainly due to the carelessness in manual operations or lack of workers. We, in this project has come up with a solution for the same. Using simple electronic components we have tried to automate the control of railway gates. As a train approaches the railway crossing from either side, the sensors placed at a certain distance from the gate detects the approaching train and accordingly controls the operation of the gate. Also an indicator light has been provided to alert the motorists about the approaching train.

Gate control

Track Switching

Using the same principle as that for gate control, we have developed a concept of automatic track switching. Considering a situation wherein an express train and a local train are travelling in opposite directions on the same track; the express train is allowed to travel on the same track and the local train has to switch on to the other track. Indicator lights have been provided to avoid collisions .Here the switching operation is performed using a stepper motor. In practical purposes this can be achieved using electromagnets.

Track Switching

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DPSK Modulation and Demodulation

Differential phase shift keying (DPSK), a common form of phase modulation conveys data by changing the phase of carrier wave. In Phase shift keying, High state contains only one cycle but DPSK contains one and half cycle. Figure illustrates PSK and DPSK Modulated signal by 10101110 pulse sequence

DPSK and PSK modulated signals

High state is represented by a M in modulated signal and low state is represented by a wave which appears like W in modulated signal DPSK encodes two distinct signals of same frequency with 180 degree phase difference between the two. This experiment requires two 180 degree out of phase carrier and modulating signals. Sine wave from oscillator is selected as carrier signal. DSG converts DC input voltage into pulse trains. These pulse trains are taken as modulating signals. In actual practice modulating signal is digital form of voice or data. Sine wave is selected as carrier and 180 degree phase shift is obtained using Opamp as shown in figure below. Different methods are used to demodulate DPSK. The analog scheme is the PLL (Phase Locked loop).

The lead and lag carrier signals

DPSK Modulation:

In DPSK, during HIGH state of the modulating signal flead signal is allowed to pass and during LOW state of the modulating signal flag signal is allowed to pass. Figure below shows DPSK [10] modulator circuit. The Opamp is tied in the inverting amplifier mode. The closed loop voltage gain of the Opamp is given by

RF + rDS (on) 3
AV(CL) = – ———————
RI + rDS (on) 1,2

Where: rDS (on) 3 is the drain- source resistance of Q3 FET
rDS (on) 1,2 is drain-resistance of the conducting FET(Q1 or Q2)

The drain source resistance is of the order of 100Ω which is very small compared to RF and RI.

Hence

RF
AV(CL) = - ——
RI

DPSK Modulator Circuit

DPSK Demodulation:

DPSK Demodulation [12,13 & 14]is done with PLL IC 565[3 4 5]. DPSK [10] signal is given as input at DPSK input terminal of PLL as shown in the figure below.
A capacitor C is connected between pin7 and power supply forms first order low pass filter with an internal resistance 3.6KW, The capacitor C should be large enough to eliminate variations in the demodulated output voltage in order to stabilize the VCO frequency. The cut-off frequency of Low pass filter is made equal to carrier frequency. The cutoff frequency of low pass filter is given by

1
fH = ———-
2pRC

R = 3.6KW, fH = 18.7KHz

The value of C designed by

1
C = ———-
2pRfH

1
C = ——————— = 2.3nF
2px3.6Kx18.7K

C selected is 3nF

DPSK Demodulator Circuit

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Device Control Using Telephone

Controlling devices using switches are common. From a few decades controlling devices using remote control switches like infrared remote control switch, wireless remote control switches, light activated switches re becoming popular. But these technologies have their own limitations. Laser beams are harmful to mankind. Some technologies like IR remote control are used for short distance applications. In such case if we have system which does not require any radiations or which is not harmful, long remote control switch!! Yes here is the solution. Here I am introducing such a system which does not require any radiations, any laser beam which has no limitation of range, I mean it can be used from any distance from meters to thousand kilometers using a simple telephone line or mobile phone.

Here I am using a telephone as a media, which serves main part of this system. By using home phone as a local phone and another phone – either landline or mobile phone as a remote phone we are controlling devices.

Features:-

1. You can control up to 10 devices. It may be any electric or electronic appliances or devices with simple to heavy appliances. Each device is given a unique code.
2. It makes accurate switching, any false switching of device are not done.
3. There is no risk for false switching.
4. Your local phone (i.e., home phone or office phone) can be used for normal use by using a DPDT switch. So you need not use a separate telephone line for this device controlling.
5. To perform any operations through remote phone line, the user needs to dial to the local telephone (to which the interfacing circuit is connected) then the respective code of the device is dialed.
6. This circuit does not require any complex IC, so any one with little knowledge of electronics can construct this circuit, because it does not need any programmable IC’s or programming.
7. This system detects the ringing signal from your exchange with the help of ring detector and automatically switches ON.
8. This device saves your money. This circuit switches OFF after a time of 60 seconds (you can change this switch ON-Time which is discussed in detail in coming section).
9. Before changing the state of the device we can confirm the present status of the device.
10. This circuit gives an acknowledgement tone after switching ON the devices to confirm the status of the device.
11. You can control devices from local telephone. It can also be controlled by PCO.

Taking a tour of the project:

This system uses Dual Tone Multi Frequency (DTMF) technology of our telephone set. Every telephone set will have this facility. We have two type of dialing facilities in our telephone system (i) Pulse dialing mode (ii) Tone dialing mode. Here this system works on tone dialing mode. The DTMF mode is shortly called as tone dialing mode. (Check for availability of tone dialing mode in your telephone set).

This system is divided into two sections

1: Remote Section:

It is nothing but remote telephone set which is present in the remote place. This may be your workspace (office / school) phone or mobile phone or a phone in PCO. Signals are sent through this telephone.

2: Local Control Section:

This is a control system through which you can control your appliances. This contains one telephone line and a control unit. The appliances to be controlled must be connected to telephone line through control unit .Control unit is kept with a sufficient backup.

What is DTMF?

When you press a button in the telephone set keypad, a connection is made that generates a resultant signal of two tones at the same time. These two tones are taken from a row frequency and a column frequency. The resultant frequency signal is called “Dual Tone Multiple Frequency”. These tones are identical and unique.

A DTMF signal is the algebraic sum of two different audio frequencies, and can be expressed as follows:

f(t) = A0sin(2*П*fa*t) + B0sin(2*П*fb*t) + ……….. ——->(1)

Where fa and fb are two different audio frequencies with A and B as their peak amplitudes and f as the resultant DTMF signal. fa belongs to the low frequency group and fb belongs to the high frequency group.

Each of the low and high frequency groups comprise four frequencies from the various keys present on the telephone keypad; two different frequencies, one from the high frequency group and another from the low frequency group are used to produce a DTMF signal to represent the pressed key.

The amplitudes of the two sine waves should be such that

(0.7 < (A/B) <>(2)

The frequencies are chosen such that they are not the harmonics of each other. The frequencies associated with various keys on the keypad are shown in figure (A).

When you send these DTMF signals to the telephone exchange through cables, the servers in the telephone exchange identifies these signals and makes the connection to the person you are calling.

Fig (A): The row and column frequencies

When you press the digit 5 in the keypad it generates a resultant tone signal which is made up of frequencies 770Hz and 1336Hz. Pressing digit 8 will produce the tone taken from tones 852Hz and 1336Hz. In both the cases, the column frequency 1336 Hz is the same. These signals are digital signals which are symmetrical with the sinusoidal wave.

Figure (B): A Typical frequency DTMF signal

Along with these DTMF generator in our telephone set provides a set of special purpose groups of tones, which is normally not used in our keypad. These tones are identified as ‘A’, ‘B’, ‘C’, ‘D’. These frequencies have the same column frequency but uses row frequencies given in the table in figure (A). These tones are used for communication signaling.

Figure (C): The frequency table

Due to its accuracy and uniqueness, these DTMF signals are used in controlling systems using telephones. By using some DTMF generating IC’s (UM91214, UM91214, etc) we can generate DTMF tones without depending on the telephone set.

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Automatic Solar Tracking System

AUTOMATIC SOLAR TRACKER starts following the SUN right from dawn, throughout the day, till evening, and starts all over again from dawn next day. On cloudy weathers, it remains still and catches the SUN again as it slips out of clouds. It does all this automatically, employs cheap and inexpensive components, and is very accurate.Let us see how it does all this.

There are three Electronic Modules to be explained. First one is the HORIZONTAL SENSOR MODULE. It employs the timer 555 in the MONOSTABLE MODE. PIN 2(Trigger Pin of 555) is hooked up with a VOLTAGE DIVIDER NETWORK(PLEASE see FIGURE 2). PIN 4(Reset) is hooked up with ANOTHER VOLTAGE DIVIDER NETWORK.

Fig 1: Block diagram of the tracker following the sun all through

Fig 2: Horizontal sensor electronic circuit

The LDR(SAY LDR A) which is always illuminated by light through FRESNEL LENS ARRAY, has Low Resistance(in presence of light resistance of LDR decreases and vice-versa). We know V(OUT)=V(IN)*[R(bottom)]/[R(bottom)+R(top)], where R stands For Resitance. So in SUNLIGHT, when LDR A’s resistance Decreases, VOLTAGE AT PIN 4 Increases. TIMER is no more RESET. PIN 2 is now lower than 1/3 rd Vcc(as the horizontal LDR 1, say LDR B does not initially receive light through its rectangular slit, so its resistance is high(Rtop=8 K ohms), consequently V(OUT) is low). This triggers the timer which gives a pulse to Decade Counter’s Clock(14) PIN and triggers it. The Decade Counter CD 4017 gives a NORMAL STEP DRIVE pulse to the Horizontal Unipolar Stepper Motor 1(coupled to the tracker unit) to rotate the tracker position so as to receive sunlight(STEP ANGLE of 2 DEGREES). This goes on till the horizontal LDR 1 is fully in SUNLIGHT(resistance low, so PIN 2’S VOLTAGE HIGH). Thus the tracker has followed the SUN Horizontally.

Fig 3: Horizontal Sensor electronic circuit

We will come to the Vertical Sensor Module, but first let us see what the DAWN LDR(SAY LDR C) does. At night the horizontal Module timer 555 remains Reset(as LDR A is in darkness so its resistance is high, thus pin 4 voltage is low, and the TRACKER points at WEST(where SUN has set). Next day when SUN rises again in the EAST, the DAWN LDR which is located at the back of the TRACKER, points at EAST. So when it receives sunlight its Resistance goes low, thus Voltage at pin 4 is high and the timer triggers the Decade Counter which in turn switches the Motor on, thus the TRACKER again moves towards the EAST. Then the TRACKER functions as previously.

Now placed with the Horizontal Sensor LDR 1 is another similar LDR 2 which receives the sunlight as and when does LDR 1. SEE FIGURE 3. So now, as LDR B(THE 1st horizontal one) receives sunlight, so does Horizontal LDR 2(SEE FIGURE 1, THESE 2 LDRs are placed together with same alignment properties and separated by an optically insulated coating(from each other).Thus when Motor 1 comes to rest, and as the second horizontal LDR (SAY LDR D),is same way coupled to the second timer’s(of Vertical Module) Reset pin as was the ALWAYS ILLUMINATED LDR A, it brings the second timer out of its Reset mode) by the previously discussed VOLTAGE RELATIONSHIP). EYE SENSOR LDR(SAY LDR E) of the tracker receives sunlight by an Anti-Reflection Coated, small Rectangular Slit, so reacts only when SUN directly points at it. The second 555’s PIN 2 is same way connected to this LDR as was the first 555’s to Horizontal LDR 1. So now that it still not receives sunlight (resistance high, so Vout low) and pin 4 is no more Reset, the second CD 4017 MAKES THE SECOND STEPPER MOTOR 2 Rotate(Coupled so as to only rotate VERTICAL SENSING BLOCK/EYE BLOCK ). This movement continues till the SUN directly points at the EYE of our TRACKER. Then the TRACKER STOPS, pointing very accurately at the SUN.FIG 2 and FIG 3 follows.

fig 4: Stepper motor control board

In figure 4 I have only shown the Horizontal Motor Control Circuit. The Vertical One uses a similar Decade Counter, NPN Transistors, Diodes(to encounter BACK EMF of Power Transistors due to Fast Switching). I chose for a Step Angle of 2 Degrees for the Unipolar Steppers. They are driven in a Normal 4 Step Sequence, first coil A is energised simultaneously with coil B ,then coil C with coil D. Thus the Motors rotate by 2 degrees each time. The Charging Interval(how long pin 3 of 555’s remains high) is almost in synchronism with the steps/second speed of the motors(here 600 steps/sec.), to avoid FALSE TRIGGERING.

NOTE:

1. For 555 in MONOSTABLE MODE, T=1.1*R*C.
2. For the FRESNEL LENS ARRAY , the standard FL 40(Focal Length=0.4 inches) Or FL 65(Focal Length=0.65 inches) FRESNEL LENSES could be used (with the Grooves facing the LDRs).
3. For the ANTI-REFLECTION COATING, MULTI-LAYER COATING could be used to minimize loss due to REFLECTION. By using alternating layers of a Low-Index material like SILICA and a Higher-Index material, it is possible to obtain Reflectivities as low as 0.1% at Single Wavelength.

CONCLUSION:
We Conclude with the ADVANTAGES of the TRACKER MODULE SYSTEM:

1. Uses SIMPLE, INEXPENSIVE ,EASY TO GET 555 timers and LDRs.
2. The whole System draws only 25 MicroAmperes of Current when the Motors are not rotating.(555 timer’s off-state current req. is very less).BATTERY POWER IS SAVED.
3. The TRACKER not only follows SUN from EAST to WEST and back to EAST in a cyclic manner(Horizontal Motor Module),but also tracks the Angular Movement of the SUN with respect to its ZENITH ANGLE to the Horizon(Vertical Motor Module and EYE).This is a VERSATILE quality for which the TRACKER could easily be used in conjunction with Solar Panels to derive maximum Solar Energy. Fast Motor Response(600 steps/sec.),no FALSE TRIGGERING, a Very ACCURATE System, it requires no Programming Devices(MICROPROCESSORS or MICROCONTROLLERS), so is NOT COMPLICATED.

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Programmable Digital IC Tester

An Integrated Circuit tester (IC tester) is used to test Integrated Circuits (ICs). We can easily test any digital IC using this kind of an IC tester. For testing an IC, we need to use different hardware circuits for different ICs; like we need a particular kind of tester for testing a logic gate and another for testing flip flops or shift registers which involves more complication and time involved will also be more. So here’s an IC tester to overcome this problem. Unlike other IC testers, this is more reliable and easier since we don’t need to rig up different kind of circuits for different kind of ICs, each time we need to test them.

Unlike the IC testers available in the market today which are usually expensive, this IC tester is affordable and user-friendly. This IC tester is constructed using 8951 microcontroller along with a keyboard and a display unit. It can test digital ICs having a maximum of 24 pins. Since it is programmable, any number of ICs can be tested within the constraint of the memory available. This IC tester can be used to test a wide variety of ICs which includes simple logic gates and also sequential and combinational ICs like flip-flops, counters, shift registers etc. It is portable and easy to use.

The block diagram of the programmable digital IC tester is as shown in below. It consists of two 8951 microcontroller ICs, a 24-pin IC socket, a keyboard unit, a display unit and indicators.

To test a particular digital IC, one needs to insert the IC into the IC socket and enter the IC number using the keyboard and then press the “ENTER” key. The IC number gets displayed in the 7-segment display unit.

Four LEDs are provided as indicators. If the IC being tested is a logic gate, then each of the 4 indicator LEDs correspond to the 4 gates of the IC. In any other case wherein the inserted IC is not a logic gate, all the 4 LEDs work as a single indicator.

Digital IC Tester

Digital IC Tester

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