In security aspects, metal detector isan essential equipment. But, the metal detector, which is available in the market today, is very costly. Hence this stands as a problem for hobbyists and for small applications. Hence we have taken an endeavor to bring out a metal detector of minimum cost.
Vineesh A. V.
Vimiya Varkey Guided BY
Viji M. C. M^. K. Gnanasheela
Ms^Sumol N. C.
Ms. Seena George
CIRCUI DESCRIPTION AND WORKING
In security aspects, metal detector isan essential equipment. But, the metal detector, which is available in the market today, is very costly. Hence this stands as a problem for hobbyists and for small applications. Hence we have taken an endeavor to: bring out a metal detector of minimum cost.
The salient features of our project is that the equipment is
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compact, simple in design and can be used practically anywhere needs. The
metal detector produces an audible alarm signal when a metallic particle comes
near to the sensor. A visible blinking LED is also there to indicate the
presence of metal.
Aivlri,..ir- Ii: iv COMPARATOR
BD139 2 .
> ' D/S
NON INV. AMPLIFIER
4. CIRCUIT DESCRIPTION AND WORKING
The circuit of metal detector is shown in Fig. 1. An astable multi-vibrator is wired around 1C 555. The free running frequency is selected as 1.2 KHz.
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In astable operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multiÃ‚Â¬vibrator. When the timer output is high, its internal discharging Tr. turns off and the VC1 increases by exponential function with the time constant (RA+RB)*C.
When the VC1. or the threshold voltage, reaches 2Vce/3. the comparator output on the trigger terminal becomes high, resetting the F/F and causing the timer output to become low. This in turn turns on the discharging Tr. and the C1 discharges through the discharging channel formed by RB and the discharging 'TV. When the VCI falls below Vcc/3. the comparator
output on the trigger terminal becomes high and the timer output becomes high asain. The discharging Tr. turns off and the VC 1 rises aaain.
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This frequency is given to the primary of the detecting transformer through a transistor. So due to the pulsating current How. a varying magnetic field will formed in me transformer. A voltage will normally induce in the secondary coil due to the mutual induction. But the transformer has no core (air core) and so the magnitude of this induced emf is very low.
detecting trans former
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When a ferrite substance conies near to the winding of the transformer, an effect of core is produced and the induced emf will be much grater than former. This voltage is amplified with the help of a non inverting amplifier build with opamp L.M324.
NON INVERTING AMPLIFIER
The amplified signal is given to the input of a voltage comparator. The reference voltage is set to a value below the magnitude of induced emf without any core. So. when the ferrite body is near to the transformer, the input of comparator is more then thai of reference pin. Then the output of the comparator goes low.
This low pulse is given to the triggering input of monostable multi-vibrator build around 555. The time is selected to 2.5 seconds and so the output will high for 2.5 seconds. The transistor BC547 starts conducting and the buzzer beeps to indicate the presence of metal. Also the LED turned off for this time.
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MONOSTAB1 .If. OPERATION
In this mode, the timer generates a fixed pulse whenever the trigger voltage falls below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low; the timer's internal flip-flop turns the discharging Tr. off and causes the timer output to become high by charging the external capacitor CI and setting the flip-flop output at the same time.
The voltage across the external capacitor CL VC 1 increases exponentially with the time constant t=:RA*C and reaches 2Vcc/3 at td=l. 1 RA*C. Hence, capacitor C1 is charged through resistor RA. The greater the time constant RAC. the longer it takes for the VC1 to reach 2Vcc/3. In other words, the time constant RAC controls the output pulse width. When the applied voltage to the capacitor CI reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop, turning the dischi irtiiim 1 r. on. At tins time, CI begins to discharge and the timer output converts to low. In this way. the timer operating in monostable repeats the above process.
The output of monostable is given to base of transistor BC547 and a buzzer is connected to the colector. So when the monostable Iriggeres, the transistor will conduct and hence the buzzer will be on and it produce a tone to indicate the presence of metal.
After the time over, the device will be read)' for next detection.
5. WINDING DETAILS OF DETECTING
The detecting trams former has a 1:1 winding (the primary and secondary has the same number of turns). The primary is wound over a 1cm diameter plastic former with 35 SWG enamaled copper wire. The primary winding has 210 turns and is wound very closely. An insulating coating is applied over the primary for isolation. Then the secondary is wounded over the primary with 40 SWG copper wire and has also 210 turns. The whole assemly is covered with a well insulator and apply warnish to allow the winding to set. The leads are taken from the primary and the secondary.
6. IMLB LAYOUT
7. COMPONENT LAYOUT
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8. COST ESTIMATION
COMPONENTS QTY RATE COST
LM324 1 14.00 14.00
LM555 2 10.00 20.00
BD139 1 3.00 3.00
BUZZER 1 40.00 40.00
DETECTING TRANSFORMER 1 300.00 300.00
3mm LED 2 . LOO 2.00
1/4W RESISTOR 10 0.25 2.50
47K PRESET 5.00 10.00
BC547 2 2.50 5.00
12-0-12/1A TRANSFORMER 1 100.00 100.00
1N4007 2 1.00 2.00
4700MFD/30V CAPACITOR 1 25.00 25.00
10MFD/25V CAPACITOR 4 2.50 10.00
0.1 MFD DISC CAPACITOR 5 1.00 5.00
14PIN IC BASE 1 2.00 2.00
8P1N IC BASE 2 1.00 2.00
LM7805 1 10.00 10.00
PCB 1 150.00 150.00 Â¢
WIRE lOMir 5.00 50.00
HANDLE 75.00 75.00
SOLDERING IRON (25W) 1 200.00 200.00
SOLDER & FLUX 1 50.00 50.00
This project has been developed considering the need for "'intelligent" low cost and longer lasting lamp. With this purpose in mind, a study has been conducted to understand about the electronic components available in the market. The equipment is compact, simple in design and can be used practically anywhere needs.
OP-AMPS and Linear Integrated Circuits by Ramakant A . Gayakwad.
fa irchild.c om
Â¢ High Current Drive Capability (200mA)
Â¢ Adjustable Duty Cycle
Â¢ Temperature Stability of 0.005WC
Â¢ Timing From p.Sec to Hours
Â¢ Turn off Time Less Than 2u.Sec
Â¢ Precision Timing
Â¢ Pulse Generation
Â¢ Time Delay Generation
Â¢ Sequential Timing
The LM555/NE555/SA555 is a highly stable controller capable of producing accurate timing pulses. With monostable operation, the time delay is controlled by one external resistor and one capacitor. With astable operation, the frequency and duty cycle are accurately controlled with two external resistors and one capacitor.
Internal Block Diagram
Ã‚Â©2002 Fairchild Semiconductor Corporation
Table 1 below is the basic operating table of 555 timer:
Table 1. Basic Operating Table
Threshold Voltage (VthMPIN 6) Trigger Voltage (VtrXPIN 2) Reset(PIN 4) Output(PIN 3) Discharging Tr. (PIN 7)
Don't care Don't care Low Low ON
Vth > 2Vcc / 3 Vth > 2Vcc / 3 High ' Low ON
Vcc / 3 < Vth < 2 Vcc / 3 Vcc / 3 < Vth < 2 Vcc / 3 High - -
Vth < Vcc / 3 Vth < Vcc / 3 High High OFF
When the low signal input is applied to the reset terminal, the timer output remains low regardless of the threshold voltage or-the trigger voltage. Only w hen the high signal is applied to the reset terminal, timer's output changes according to threshold voltage and trigger voltage.
When the threshold voltage exceeds 2/3 of the supply voltage while the timer output is high, the timer's internal discharge TV. turns on. lowering the threshold voltage to below |/3 of the supply voltage. During this time, the timer output is.maintained low. Later, if a low signal is applied to the trigger voltage so that it becomes I/3 of the supply voltage, the timer's internal discharge Tr. turns off. increasing the threshold voltage and driving the timer output again at high.
Figure 1. (Vlonoalable Circuit
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Figure 3. Waveforms of Monostable Operation
1. Monostable Operation
Figure I illustrates a monostable circuit. In this mode, the timer generates a fixed pulse whenever the nigger voltage falls below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low. the timer's internal flip-flop turns the discharging Tr. off and causes the timer output to become high by charging the external capacitor CI and setting the flip-flop output at the same time.
The voltage across the external capacitor C1. Vci increases exponentially with the time constant 1=Ra*C and reaches 2Vce/3
at ld=l. I Ra*C. Hence, capacitor CI is charged through resistor Ra. The greater the time constant RaC. the longer it lakes
for the Vci to reach 2Vcc/3. In other words, the lime constant RaC controls the output pulse w idth.
When the applied voltage lo the capacitor C1 reaches 2Vcc/3. the comparator on the trigger terminal resets the Hip-flop.
turning the discharging Tr. on. Al this time. CI begins lo discharge and the timer output converts to low.
In this way. the timer operating in monostable repeals the above process, figure 2 shows the time constant relationship based
on Ra and C. figure 3 shows the general waveforms during monostable operation.
It must be noted that, for normal operation, the trigger pulse voltage needs to maintain a minimum of Vcc/3 before the timer output turns low. That is. although the output remains unallected even if a different nigger pulse is applied while the output is high, it ma\ he affected and the waveform not operate properly if the trigger pulse voltage al the end of the output pulse remains al below Vcc/3. I'igure -I shows such timer oulpul abnormality.
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Figure 4. Waveforms of Monostable Operation (abnormal) 2. Astable Operation
kT#@ LM224 - LM324
LOW POWER QUAD OPERATIONAL AMPLIFIERS
Ã‚Â¦ WIDE GAIN BANDWIDTH : 1.3MHz
Ã‚Â¦ INPUT COMMON-MODE VOLTAGE RANGE INCLUDES GROUND
Ã‚Â¦ LARGE VOLTAGE GAIN : 100dB
9 VERY LOW SUPPLY CURRENT/AMPLI : 375|iA
Ã‚Â¦ LOW INPUT BIAS CURRENT : 20nA
Ã‚Â¦ LOW INPUT OFFSET VOLTAGE : 5mV max. (for more accurate applications, use the equivÃ‚Â¬alent parts LM124A-LM224A-LM324A which feature 3mV max.)
Ã‚Â¦ LOW INPUT OFFSET CURRENT : 2nA
Ã‚Â¦ WIDE POWER SUPPLY RANGE : SINGLE SUPPLY : +3V TO +30V
Ã‚Â¦ DUAL SUPPLIES : Ã‚Â±1.5V TO Ã‚Â±15V
These circuits consist of four independent, high gain, internally frequency compensated operationÃ‚Â¬al amplifiers. They operate from a single power supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage.
(Thin Shrink Small Outline Package)
Output 1 1 C
Inverting Inpul 1 2 
Non-inverting Input 1 3
vfcc* 'I C
Non-inverting Input 2 5 Ã‚Â£ \t
Inverting Input 2 6 L~
Output 2 7 Ã‚Â£
PIN CONNECTIONS (top view)
05 ./ V [06
Non-inverting ; ; input .
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Â¢ - |Q11
Q8 |" |Q9
foiO * | Q12
777, 777, ^777, 777, 777, GND
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter LM124 LM224 LM324 Unit
Vcc Supply voltage Ã‚Â±16 or 32 V
Vi Input Voltage -0.3 to +32 V
Vid Differential Input Voltage 1' + 32 V
Plot Power Dissipation N Suffix
D Suffix 500 500 400 500 400 mW mW
Output Short-circuit Duration z) Infinite
'in Input Current 3' 50 50 50 mA
^oper Opearting Free-air Temperature Range -55 to +125 -40 to +105 0 to +70 Ã‚Â°C
Tstg Storage Temperature Range -65 to +150 X
dnuii-LiiLuu^ iFuui me uuipui iu v^*^ lchi LdUbe excessive neduny u vpc > ov. i ne maximum uuipui currer of the magnitude of Vcc. Destructive dissipation can result from simultaneous short-circuit on all amplifiers.
Either or both input voltages must not exceed the magnitude of Vcc* or Vcc".
Short-circuits from the output lo VCC can cause excessive healing if VgC > 15V. The maximum output current is approximately 40mA independent
This input current only exists when the voltage at any of the input leads is driven negative. It is due to the collector-base junction of the input PNP transistor becoming forward biased and thereby acting as input diodes clamps. In addition to this diode action, there is also NPN parasitic action on the IC chip, this transistor action can cause the output voltages of the Op-amps to go lo the Vcc voltage level (or to ground for a large overdrive) for the time duration than an inpul is driven negative.
This is not destructive and normal output will set up again for input voltage higher than -0.3V.
TYPICAL SINGLE - SUPPLY APPLICATIONS
HIGH INPUT Z ADJUSTABLE GAIN DC INSTRUMENTATION AMPLIFIER
t J 1/4
iLM124 R3 100k R4 100k
R2 2k I T o R5 100k Ã‚Â¦ 1/4 <V. .LM124
:|_M124 R6 100k R7 100k
if Rl - R5 and R3 - R4 = R6 = R7
e0 = ''Â¢Ã‚Â£1 (e2 -e,) -Ã‚Â¦
As shown e0 = 101 (e2-.en).
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SEMICONDUCTOR TECHNICAL DATA
Order this document by BC546/D
BC547, A, B, C
BC548, A, B, C
CASE 29-04, STYLE 17 TO-92 (TO-226AA)
â€ â€ (M) MOTOROLA
Ã‚Â© Motorola. Inc. 1996
Medium Power Linear and Switching Applications
Â¢ Complement to BD136, BD138 and BD140 respectively
1. Emitter 2.Collector 3.Base
NPN Epitaxial Silicon Transistor
Absolute Maximum Ratings TC=25Ã‚Â°C unless otherwise noted
Symbol Parameter Value Units
VCBO Collector-Base Voltage : BD135 45 V
BD137 60 V
BD139 80 V
VfJEO Collector-Emitter Voltage BD135 45 V
BD137 60 V
BD139 80 V
VEBO Emitter-Base Voltage 5 V
lc Collector Current (DC) 1.5 A
'CP Collector Current (Pulse) 3.0 A
lB Base Current 0.5 A
Pc Collector Dissipation (TC=25Ã‚Â°C) 12.5 W
Pc Collector Dissipation (Ta=25Ã‚Â°C) 1.25 w
Tj Junction Temperature 150 c
TSTG Storage Temperature - 55 - 150 Ã‚Â¦ =c
Electrical Characteristics Tc=25Ã‚Â°C unless otherwise noted
Symbol Parameter Test Condition Min. Typ. Max. Units
VCE0(sus) Collector-Emitter Sustaining Voltage : BD135 : BD137 : BD139 lc = 30mA, lB = 0 45 60 80 V V V
'CBO Collector Cut-off Current VCB = 30V, lE = 0 0.1 uA
'EBO Emitter Cut-off Current VEB = 5V. Ic = 0 10 pA
hFE1 nFE2 hFE3 DC Current Gain : ALL DEVICE : ALL DEVICE : BD135
: BD137, BD139 VCE = 2V, lc = 5mA VCE = 2V, lc = 0.5A VCE = 2V, lc = 150mA 25
25 40 40 250 160
VCE(sat) Collector-Emitter Saturation Voltage lc = 500mA, lB = 50mA 0.5 V
VBE(on) Base-Emitter ON Voltage VCE = 2V, lc = 0.5A 1 V
3-Terminal 1A Positive Voltage Regulator
Output Current up to IA
Output Voltages of 5. 6. 8. 9. 10. 12. 15. 18. 24 V Thermal Overload Protection Short Circuit Protection
Output Transistor Sale Operating Area Protection
The KA78XX/KA78XXA series of tin 'ce-tcrminul positive regulator are available in the TO-220/D-PAK package and with several fixed output voltages, making them useful in a wide range of applications. Each type employs internal current limiting, thermal shut down and safe operating area protection, making it essentially indestructible. If adequate heal sinking is provided. the\ can deliver over IA output cunenl. Although designed primarily as fixed voltage regulators, these devices can be used with external components lo obtain adjustable \oltages and currents.
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Ã‚Â©2001 Fairchild Semiconductor Corporation