Pulse Generator
COMPONENTS REQUIRED:
COMPONENT QUANTITY
i. Transformer 220/9V 1
ii. Diode PN 4
iii. Capacitor 1000µf/15V 1
iv. Regulator LM 7805 1
v. Capacitor 100 µf 2
vi. Capacitor 0.01 2
vi. Variable Resistance (0-1M?? 2
vii IC 555 2
viii LED 2
ix. IC Base 2
x. Resistance 330
xi. Connecting
Wires 3 m
xii. Multipurpose PCB 2
xiii. Accessories (Cabinet, cord, switches)
xiv. Relay 6v 1
Circuit is made up of two section.
1. Power supply :
Above is the circuit of power supply. The AC mains is stepped down by transformer to deliver a secondary output of 9V. The transformer output is rectified by a full wave bridge rectifier, filtered by capacitor and regulated by the 7805 regulator. Unregulated supply can be used for operating the relay.
2. Main circuit :
Construction: In order to achieve independent on and off time for the produced pulse. Two 555 timer IC is taken, one will take care of the on time of the pulse and other will control the off period of the pulse. Both 555 IC is made to work in monostable mode. That is it has only one stable state and required trigger for achieving timing pulse. The reset pin of both the IC is connected to VCC, in order to avoid any false triggering. The output of one is connected to the trigger pin of the other. A variable resistances of 1M??is used between pin 7 and 8, in order to vary the time period of pulse. Led’s are connected in order to indicate the outputs from two IC.
Operation:
When circuit is initiated by triggering the first IC the output of it goes high. This will also indicated by the glow LED. After remaining high for certain time period output goes low which in turn trigger the other IC whose output goes high for certain time period
depending on the resistance set between pin 7 and 8. When it’s output goes low it will trigger the first. This cycle continues. The pulse from these IC’s can be used with relay.
Timing diagram:
It has been illustrated above that both the IC’s are working alternately. Therefore the timing pulses from two IC’s for some ON and OFF period can be drawn below:
Setting time period:
The time period of pulse depend on the value of resistance connected between 7 and 8 pin, and value of capacitance connected to 6 pin. Here we have keep the value of capacitance constant and use variable resistance. The variable resistance on IC 1 is used to set ON time and that is on IC 2 is used to set OFF time of resultant output pulse from the circuit.
The time period is govern by the following formula:
T= 1.1*R*C
Where T=time period of output pulse of respective IC
R=variable resistance connected between pin 7 and 8
C=fixed capacitance connected to the pin 6.
The maximum ON or OFF time which can be achieved by the above circuit can be calculated as follow:
T=1.1*10*10^6*100*10^-6
= 110 sec
Since the maximum value of resistance between pin 7 and 8 is ????and that of the capacitance is
100 µf.
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