Generally the standard line frequency in some country is 50HZ or in some countries 60HZ, which may vary time to time. Due to this varying nature of frequency, sensitive equipment may start malfunction, and the requirement result we may not get. New here is a simple mains line frequency mater designed and verified at BEP (Best engineering project) lab used to measure the frequency of AC mains.
Circuit description mains line frequency meter
The circuit of mains line frequency mater is build around timer IC2 (NE555), oscillator-cum-driver IC (IC3), decode counter, AND gate IC (IC6), seven segment display and 6 volt regulator IC. The AC mains input (230v) is stepped down using 9v-0-9v step down transformer. The output from secondary winding is rectified by rectifier diode D1 and D2 which further filtered by capacitor C1 and given to input of voltage regulator IC (IC1) to produced regulated 6v DC.
The stepped down 9v is connected to pin 2 and 6 of IC2 (timer IC) for converting the sine wave into square wave frequency.
This converting is done because square wave is more suitable for the circuit operation then sine wave.
The 10HZ clock pulse is generated by IC3 which is wired as oscillator-cum-divider. The outputs 10HZ clock pulse is given to the clock pin 14 of decode counter IC5 (4017).IC5 divides 10HZ clock by 10 to obtain 1 HZ clock pulse. The output of IC3 from pin 3 is again fed into its input pin through VR1 and R4. Capacitor C2 is used as charge/discharge capacitor and is connected between input of IC3 and ground. The value of output frequency from IC3 is depended upon VR1, R4 and capacitor c2, the value of this component is so selected that its output is accurate 10 HZ clock pulse.
LED1 is connected to output pin of IC4 gives one flash per second to indicated 1HZ clock pulse. The 1HZ clock pulse is connected to another decode counter clock pin 14 of IC5. The output from pin 3 is given to pin 2 through resistor R7 and square wave output from IC2 is given to pin 1 to IC6. Therefore, the unknown frequency of AC mains line, applied to pin 1 of AND gate (IC6) passes through it for only one second and connected by IC7 and IC8.
IC7 and IC8 are configures to drive 7-segment display DIS 1 and DIS2 respectively to display the frequency. DIS1 is used to display unit place of frequency and DIS2 is used for tens place.
This circuit is so designed that it is auto-reset circuit, but you can select the reset time of 1 second to 5 seconds using rotary switch SW2, which is connected to reset pin of IC2, IC7 and IC8. For long time display of the frequency, keep the knob of rotary switch SW2 towards fifth position. For instant see any variation in the supply frequency keep the knob of rotary SW2 towards fifth position. For instant see any variation in the supply frequency keep the knob of switch SW2 to position 1.
PARTS LIST OF MAINS LINE FREQUENCY METER
Resistor (all ¼-watt, ± 5% Carbon)
R1, R5, R6, R7 = 1 KΩ
R2, R3 = 1 MΩ
R4 = 10 KΩ
R8, R11 = 100 KΩ
R9, R10 = 470 Ω
VR1 = 47 KΩ
C1 = 1000 µF/25V
C2 = 47 µF/16V
C3 = 0.01 µF
IC1 = LM7806
IC2 = NE555
IC3 = CD4093
IC4, IC5 = CD4017
IC6 = 7408
IC7, IC8 = CD4033
D1, D2 = 1N4007
DIS1, DIS2 = LT543
SW1 = Rotary Switch
X1 = 230V AC primary to 9V-0-9V 250mA secondary transformer