 In today's session, we are going to see a stable multi-operator using IC-555 timer. At the end of today's session, students will be able to explain IC-555 timer as a stable multi-operator with the help of circuit diagram and output signal waveform. These are the contents of today's presentation. An stable multi-operator also known as free-running multi-operator generates a rectangular wave signal of required frequency. This multi-operator does not require any external trigger signal to change the state of output signal. Hence, it is known as free-running multi-operator. As no any state of output signal is stable, that is why this multi-operator is known as a stable multi-operator. This circuit is designed by connecting two external registers and a single capacitor to basic IC-555 timer IC as shown in Figure 1. Now, this figure shows the circuit diagram for a stable multi-operator using IC-555 timer, the two registers RA and RB and a single capacitor connected between pin number 6, 2 and ground. And additional capacitor C1 is connected between pin number 5 and ground. And output is taken from pin number 3. With reference to Figure 1, pin number 1 is connected to ground, pin number 4 and pin number 8 are shorted together and then connected to plus Vcc, DC power supply voltage. The output is taken from pin number 3. Pin number 6 and pin number 2, those are three-should input for upper comparator and trigger input for lower comparator are shorted together and then connected to ground through external capacitor C. Pin number 7 is connected to plus Vcc through external register RE. Register RB is connected between pin number 6 and pin number 7. At pin number 5, additional bypass capacitor of 0.01 microfarad is connected with respect to ground to avoid any noise problem. Now this is another circuit diagram. Figure number 2 can be used to discuss the working of a stable multi-operator using IC-555. This figure includes internal functional block diagram of IC-555 with external components register RA, RB and C. As shown in Figure 2, when Q output of internal flip-flop is at low or that is the timer output is at high voltage level, the external, the internal register transistor is off and external capacitor C starts charging towards plus Vcc through register RA and RB. The charging time constant of capacitor is RA plus RB into C. As C charges, the voltage across capacitor goes on increasing that is applied to non-invoting input of upper comparator that is three-should voltage increases as shown in Figure 3. After some time, a three-should voltage across a capacitor just exceeds a two-thread Vcc. The output of upper comparator that is comparator 1 becomes high so this sets internal flip-flop so that its Q output becomes high and Q bar output becomes low. So Q bar output of internal flip-flop so that is nothing but the final output of IC-555 timer so timer output becomes low. Students should pause video here and think or how does timer output becomes high again with Q output of internal flip-flop is at high voltage level the internal transistor that is discharge transistor is turned on and P number 7 is grounded through discharge transistor. So external capacitor C charges through register RB, discharges through register RB with discharging time constant RB into C with C discharging the trigger voltage at P number 2 that is voltage across capacitor goes on decreasing as capacitor discharges. So that is applied to inverting input of a lower comparator 2. So the trigger voltage at inverting input of comparator 2 decreases when it becomes just less than one-third Vcc so output of comparator 2 becomes high. So this resets internal flip-flop its Q output becomes low and its Q bar output becomes high so Q bar output of internal flip-flop that is a timer output available at P number 3. So output signal of IC-555 will be at high voltage level thus the timer output state automatically changes from low voltage level to high voltage level. Again from high voltage level to low voltage level as shown in figure 3 and this is repeated continuously and we are getting continuous rectangular signal at the timer output. This figure 3 shows the output waveform for a stable multivibrator using IC-555 the upper waveform is for output signal of IC-555 so output voltage signal changes between 2 voltage levels high voltage levels that is approximately equal to plus Vcc and a low voltage level that is nearly 0 voltage level and the second waveform lower waveform is for the voltage appearing across external capacitor. The external capacitor charges from one-third Vcc to two-third Vcc so voltage across capacitor goes on increasing from one-third Vcc to two-third Vcc during which the timer output remains at high voltage level when the capacitor voltage just exceeds two-third Vcc again the internal transistor becomes on and so capacitor discharges. So capacitor discharges from two-third Vcc up to one-third Vcc when voltage across capacitor just falls below one-third Vcc again the internal comparator 2 switches internal flip-flop so that it is cuber output becomes high cuber output becomes high and the final timer output becomes high so as the voltage across capacitor just falls one-third Vcc again the timer output becomes high. So, Tc is the time duration for which C charges from one-third Vcc to two-third Vcc and Td is the time duration for which the C discharges from two-third Vcc to one-third Vcc the frequency of output signal depends on the values of external components like resistor RA, RB and capacitor C the time duration in which C charges from one-third Vcc to two-third Vcc is equal to the time for which the output is high it is given by Tc Tc stands for charging time that is Tc is equal to 0.693 into RA plus RB into C the time duration in which C discharges from two-third Vcc to one-third Vcc is equal to the time for which the output is low so the discharging time is given by Td is equal to 0.693 into RB into C the time period of output signal is given by the total time duration for charging of capacitor and discharging of capacitor charging time interval plus discharging time interval T is equal to Tc plus Td so total time period is equal to T equal to 0.693 into RA plus 2 RB into C seconds the frequency of output signal that is continuous oscillations is given by the frequency is reciprocal of a time period so f equal to 1 upon T is equal to 1 upon 0.693 into RA plus 2 RB into C so that is equal to 1.44 upon RA plus 2 RB into C the time period T of output signal of Ic triple fire timer is independent of plus Vcc DC power supply voltage we can express a duty cycle of Ic triple fire timer signal the duty cycle of output signal is the ratio of time Tc during which the output is at a high voltage level to the total time period of output signal it is given by a percentage D is equal to Tc upon T multiplied by 100 the Tc stands for charging time and T stands for total time period of output signal so percentage D D stands for duty cycle is equal to RA plus RB divided by RA plus 2 RB multiplied by 100 this is a reference thank you.