 Professor, Electronics and Telecommunication Engineering, Walchand Institute of Technology, Solapur. Today, we will discuss frequency ratio measurement using IC-74C 926. In last video, we saw how to measure frequency of a given signal by using IC-74C 926. Using outcome, at the end of this session, students will be able to describe frequency ratio measurement scheme using IC-74C 926. Contents, frequency ratio measurement scheme will be described by using block diagram first and then the frequency ratio measurement scheme will be explained using timing diagram. So, let us see the block diagram of frequency ratio measurement scheme. As usual, we have this 7-4C 926 which is a 4 digit decayed counter with display driver circuitry. Since there are 4 digit decayed counters, there are 4 7-segment displays are required which are connected and these are driven in a multiplexer fashion so that these transistors are controlled by using these control signals A, B, C, D and this is mainly a counter which counts the clock pulses given to it and whenever counting is over, we can store these count value into an internal latch by activating this latch enable input named as Y and after latching the data, now the counter is ready for the next measurement cycle by making this reset input high called as Z input and the display select input of this IC-74C is permanently grounded such that so that we get latch data to be displayed on these 7-segment displays. So, whatever latch data after measurement is displayed here. Now, in frequency ratio measurement scheme, there are 2 frequencies one is high frequency and another is low frequency so we are finding the ratio of these 2 frequencies so to find out the ratio of 2 frequencies what is done is the high frequency signals are given through this input interface which is used as a signal conditioning circuit so that the output of this is compatible to this digital logic gate so whatever the frequency input signal frequency whether it is a sinusoidal or any type of other signal can be here converted into digital that is a square wave and then appropriately voltage levels are maintained by using this input interface circuit and then it is given to the AND gate of the input to the AND gate. And another input of the AND gate is coming from the flip-lof which divides the input frequency by 2 and the input frequency is another frequency which is called a low frequency signal which is again given through this input interface which is used for signal conditioning of the input signal so what we get here at the output of flip-lof is the time based signal used for frequency ratio measurement so this time based signal will be a time period of low frequency signal that means this signal or this input of the AND gate will be remain high will remain high for exactly one period of this low frequency signal. So what we are doing here is we are counting the high frequency pulses we are counting because this AND gate output is given as a clock input to the 74C926 so this clock pulses are counted for exactly one period of low frequency signal that means we get a frequency ratio between this high frequency and low frequency. So this way we can find out the ratio of these two unknown frequencies and this control signal block is used to generate the latch enable input at the end of the time period of low frequency signal that means whenever time period of this low frequency signal is over this latch enable input is activated and the data is latched into this counter and it will be displayed on this seven segment displays and to make this device ready for the next measurement we should again reset this counter to zero so that is done again by this control signal by generating this reset signal just after this latch enable input is activated. So first latch enable signal is generated then reset is generated. So this way we can measure a frequency ratio. Here since these are decayed counters or inside this seven four C926 there is a decayed counter we can display a maximum number on these four digits is 9999. So here we can measure a frequency ratio of two frequencies with a maximum limit of 9999. Let us understand the operation of frequency ratio measurement setup using this timing diagram. Here the first what we have drawn is a low frequency signal the low frequency signal one time period is shown here from this to this. So for first half cycle this is high and it is low then this is given to the flip-flop and flip-flop output gives us a high pulse of this much duration that means high pulse for time period of the low frequency signal is given and the counter counts this high frequency pulses for exactly this much period that means in one time period of a low frequency signal how many clock pulses are there of high frequency signal is found and that is what the frequency ratio. So at the end of the time period of low frequency signal that means at this point latch enable is activated. So at this point the data is latched into the internal counters and it will be displayed on the seven segment displays and after that the reset is also activated just after this latch enable because now the counter becomes ready for the next measurement cycle. So this way frequency ratio measurement setup is done. Let us have a question what is the maximum ratio of two frequencies that can be measured using IC747926. You pause the video and answer the question. As we have seen earlier the maximum that we can display here is 9999 so naturally the maximum frequency ratio that can be measured using this IC747926 will be 9999 only but since we are counting from 0 the maximum ratio that we can count is 10,000 0 to 9999. So the answer is maximum ratio that can be counted by using IC747926 is 10,000. These are my references. Electronic system designed by Vaibhav T. Tarate, Electrotech Publication Satara. Thank you very much.