Seven Segment
Counter
Display Circuit
Electronic toss
circuit
Mains failure alarm
circuit
Photo Switch
Circuit using 555 IC
Two transistor
siren
Touch Switch
Circuit using NE
555
10 minute timer circuit
selective timer alarm
Seven Segment Counter
Display Circuit
Seven Segment Counter Display Circuit
Description
 Here 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.
Cont. >> Seven Segment Counter Display Circuit
Mains failure alarm
circuit
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.
Cont. >> Mains failure alarm
circuit
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.
Photo Switch Circuit using 555 IC
Photo Switch Circuit using 555 IC
Description
 This 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.
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.
Cont. >> Photo Switch Circuit using 555 IC
Electronic toss circuit
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.
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.
Cont. >> Electronic toss circuit
Two transistor siren
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.
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.
cont. >>Two transistor siren
Touch Switch Circuit
using NE 555
Touch Switch Circuit using NE 555
Description
 This 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.
Cont. >> Touch Switch Circuit using NE 555
10 minute timer circuit
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.
Cont. >> 10 minute timer circuit
selective timer alarm
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.
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 
Cont.>> selective timer alarm
Thanks