3 Seven Segment Counter Display Circuit DescriptionHere is the circuit diagram of a seven segment counter based on the counter IC CD 4033.This circuit can be used in conjunction with various circuits where a counter to display the progress adds some more attraction.IC NE 555 is wired as an a stable multivibrator for triggering the CD 4033.For each pulse the out put of CD 4033 advances by one count . The output of CD 4033 is displayed by the seven segment LED display LT543.Switch S1 is used to initiate the counting . Diode D1 prevents the risk of accidental polarity reversal.
6 Mains failure alarm circuit Description.Here is a simple mains failure alarm circuit that produces an alarm whenever the mains supply fails . Lot of such circuits are available , but the peculiarity of this circuit is that it requires no back up power source like a battery to power the alarm when the mains is absent.When there is mains supply the transistor Q1(BC558) will be OFF and the capacitor C1 will be charged . When the mains supply fails the transistor Q1 becomes ON and the capacitor C1 discharges through the Q1 to drive the buzzer to produce an alarm . The capacitor C2 is the filter capacitor for the bridge . Diode D2 prevents the discharge of the C2 when mains fails . If D2 is not there ,the alarms will remain silent for a time capacitor C2 to fully discharge after the power failure.
8 Cont. >> Mains failure alarm circuit Notes T1 can be a 230V primary 6V secondary 500mA transformer.B1 can be a 1A bridge.You can make the same using four 1N 4007 diodes.All capacitors are rated 25V.You can use any general purpose PNP transistor (like BC158,BC177 etc) as Q1.
10 Photo Switch Circuit using 555 IC DescriptionThis is a simple photo switch suitable for home and industrial purpose . The circuit switches on a relay when the light intensity falling on the sensor crosses the set limit.The circuit is based on a NE 555 and two transistors for driving the relay . The resistor R1 is adjusted such a way that under normal condition the voltage across the LDR is less than 1/3 the supply voltage . In this condition output of IC is high .This makes transistor Q1 on .Transistor Q2′s base is connected to collector of Q1.So Q2 will be off keeping the relay de energized . When light falls the voltage across LDR rises above 2/3 Vcc .This makes the output of IC go high making the relay to energized . The result we get a relay that operates according to the intensity of light falling on the LDR.
11 Cont. >> Photo Switch Circuit using 555 IC Notes .Assemble the circuit on a good quality PCB or common board.To setup the circuit switch on power supply , connect a multimeter across LDR and adjust R1 so that voltage across LDR is just below 1/3 supply voltage . Ensure that relay is off in this condition . If not reduce voltage across LDR further more by adjusting R1 to make relay off.Now cover the top of LDR using a black paper and see the relay gets activated . If not, make further adjustments with R1.Nothing to care after some trial and error you will get the correct set piont of R1 where the circuit works . This circuit is nothing great , but some simple basics . I have tested this and got good results . So no problem .Just proceed.If there is some chattering in the relay , that may be because off the difference between the turning on and turning off voltages . This can be avoided by connecting a resistor whose value is equal to 1/2 the resistance of LDR at illuminated condition.
14 Electronic toss circuit Description.The circuit given here can be used for tossing head or tail. There are many games in which a tossing is required to start and this circuit can be used in all such instances.The circuit uses two ICs NE 555 timer (IC1) and 74LS76 dual JK flip flop (IC2).The IC 1 is wired as an a stable multi vibrator operating at 10Hz.The output of IC1 is inverted by using the transistor Q1.The collector of Q1 is connected to the pin 1 of IC2 via the push button switch S1.The IC2 is wired in toggle mode. When push button S1 is pressed the output pins 14 and 15 of IC2 starts toggling in state. The LEDs connected to these pins also toggles (Since the frequency of toggling is 10Hz, we feel both LEDs glowing).When push button S1 is released either one of the LED remains ON indicating the head or tail.
15 Cont. >> Electronic toss circuit Notes.The circuit can be powered from 5 V DC.Switch S1 is a push button switch.The ICs must be mounted on holders.The circuit can be assembled on a general purpose PCB.
18 Two transistor siren Description. Here is the circuit diagram of a simple two transistor alarm circuit that can be operated from a 9V PP3 battery. Here the two transistors are wired to form an oscillator whose frequency increases when switch S2 is pressed and decreases when S2 is released. In order to attain this the base of Q1 is biased from an RC circuit comprising of R2 and C1.When S2 is pressed C1 is charged through the resistor R2.As the voltage across the C1 increases the time constant decreases and this results in an increases in the frequency. When S2 is released capacitor discharges and the frequency of the tone decreases. The sound heard from the speaker will be almost like that of a siren.
19 cont. >>Two transistor siren Notes.The circuit can be assembled on a Vero board.Use a 9V PP3 battery for powering the circuit.Switch S2 can be a miniature push button switch.The type no of transistors are not very significant here.
22 Touch Switch Circuit using NE 555 DescriptionThis is the circuit diagram of a small touch plate controller using IC NE 555 .This circuit is ideally useful for making touch operated doorbells, buzzers , toys etc which when touched on the touch plate operates the relay for a preset time and the turns off automatically.This circuit is realized by utilizing the high input impedance of trigger pin of the 555 IC . When the IC is triggered by the induced voltage of human body the output goes high for a time determined by R1 and C1.The transistor is used to drive the relay . The relay contacts can be used to drive the load like bell, motor , lights etc.Notes.To make the touch plate cut a 1 square cm thin metal sheet.To setup the circuit connect to power supply and adjust R1 while keeping touching on the touch plate . Stop at the point where relay activates . If relay is in the activated state initially then do the same until the relay is deactivated.
25 10 minute timer circuit Description. When ever you need to get an alarm or intimation after ten minutes ,the circuit shown below can be used.The circuit is nothing but a monostable multivibrator based on IC NE 555.When ever you press the reset push button the green LED D1 glows after 10 minutes.Notes.Assemble the circuit on a good quality PCB or common board.The time duration can be set by varying the POT R5.The switch S1 can be a push button switch.The IC1 must be mounted on an IC base.
28 selective timer alarm Description. A timer circuit using IC 4060 is given here. The IC 4060 is a 14 stage binary counter with a built-in oscillator.R2, R7, C1 are the components that determine the frequency of the oscillator and the outputs will become high one after other and only one at a time. The last five outputs are only used here. The high pulses from the outputs are used to trigger the NE555 IC. Here NE555 is wired as a monostable multivibrator. The buzzer will produce the alarm when the output of IC2 goes high. The duration of the alarm depends on the components C3 and R5.The duration can be adjusted by varying the value of C3.The alarm will automatically turn OFF after the predetermined time. The trigger pin of IC2 will be normally positive. When the Q1 is forward biased by the positive pulse at its base from IC1, the capacitor C2 becomes charged and reduces the voltage at trigger pin of IC2.This triggers the IC . When the capacitor is fully charged the pin 2 becomes again positive. The maximum duration from timer IC 4060 will be at pin 3. The times decrease by half in the pins 2, 3, 15, and 13 respectively. The timer duration can be varied by varying the capacitor C1.
29 Cont.>> selective timer alarm Notes.Use 6V DC for powering the circuit.Assemble the circuit on a good quality PCB.Mount the ICs on holders.The switch S2 can be a single pole five throw rotary switch.The switch S1 can be a push button switch.S1 is used to reset the timer.S2 is used to select the alarm time.R7 can be used for the fine adjustment of alarm time