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The essence of the circuit is for the input of tone and signal to provide an activation for the relay switch. Relay – an electrically operated switch where the current flowing through the coil of the relay is creating a magnetic field which attracts a lever and changes the switch contacts, thereby making its state open or close BC214 – a complementary silicon planar epitaxial transistor used in AF small signal drivers and am1 as well as for low noise preamplifier applications due to its feature of good linearity of DC current gain LM741 – a general purpose single operational amplifier with features such as offset null, compensated internal freq uency, voltage range with high input, good stability of temperature, and protected from short circuit The use of relay will allow the circuit to switch from one condition to another. It can also be referred to as a form of an electrical amplifier since it is able to control an output circuit of higher power than the input circuit. There are man...

This circuit is able to identify PAL and NTSC video signals. Its output is high for an NTSC signal and low if the signal is PAL. This output signal can be used, for example, to automatically switch in a colour subcarrier converter or some other device while an NTSC signal is being received. One application is for the reception from satellites of 'free-to-air' TV signals, which in Australia generally contain a mixture of 625-line PAL and 525-line NTSC programs. Operation of the circuit is as follows. IC1 is an LM1881 video sync separator which takes the video input signal and generates vertical synchronisation pulses. For an NTSC signal, these pulses are 16.66ms apart, corresponding to the 60Hz field rate, while for a PAL signal they are 20ms apart, corresponding to the 50Hz field rate. The vertical sync pulses are fed into IC2a, the first of two dual retriggerable monostable multivibrators in the 74HC123A. IC2a has a period of very close to 17.9ms, set by the 200kO resistor a...

Simple phase shift measurement can be done by squaring both the measured and the reference, then compute the difference of the two signals. The accuracy of the circuit shown in the schematic d iagram  below is 1% UP to 2000 cps. This circuit is used in computers and for high speed analog instrumentation. Negative value for zero phase shift is indicated by the zero center DC ammeter, zero for 90′ phase shift and some maximum value for 180′ phase shift.  Phase-Shift Meter for Audio Frequency Signal Circuit Diagram