 assistant professor, electronics and telecommunication engineering, Walchand Institute of Technology in Sallapur. Today, we will discuss frequency measurement using IC-74C 926. In the last video, we saw IC-74C 926 details. Learning outcome, at the end of this session, students will be able to describe frequency measurement using IC-74C 926. Contents, we will see first the block diagram of frequency measurement, then we will see the timing diagram of frequency measurement scheme and finally we will see time base and control signal generation which is required for the IC-74C 926. Let us see the block diagram of frequency measurement. Here, this is what IC-74C 926 and its associated displays, there are four seven segment displays which are driven by these four transistors and controlled by these lines A, B, C, D. Since this is a multiplexer display system, here we are giving latch enable input to the counter, reset input to the counter, also clock input to the counter is given and here we have tied display select to the ground. When display select is connected to ground, the latch data in the counters will be displayed here. So, let us see how to measure the unknown frequency. Unknown frequency is applied here, which is given to the block called as a input interface, wherein the input frequency signal, unknown frequency signal is converted into the appropriate signal levels by using this input interface and then it is given to one of the input of AND gate and the other input of AND gate is coming from this time base output we can say 1 megahertz is divided by a count value. So, such that we get 1 hertz here, output of this 1 hertz is given to the flip-flop and this when it is given to the flip-flop, it comes out to be 0.5 hertz. That means, the on period will be 1 second, off period will be 1 second, whereas in 1 hertz signal on period will be 0.5 second and off period will be 0.5 second. This is input frequency is given to the clock input of the 7 4 C 9 to 6 for exactly 1 second. That means, we get the input frequency in hertz. So, here this AND gate is used for getting this unknown frequency input signal and this unknown frequency input signal is passed exactly for 1 second and whatever count we get at the output of this display will be the frequency in hertz because we know the frequency means cycles per seconds. So, since these cycles or unknown frequency signal is fed to the clock input of 7 4 C 9 to 6 exactly for 1 second directly whatever we get here is a frequency in hertz. So, this way in the frequency measurement what is important here is this obtaining 1 second on period. This 1 second on period is obtained by using this 1 megahertz crystal oscillator, then it is divided by a frequency divider network such that we will get 1 hertz here. This 1 hertz is passed through a flip-off and we get 0.5 hertz. So, 0.5 hertz means can on period, 1 second off period. This is what the counting of pulses unknown pulses. Here another very important is time base and counter control signal generation is needed. From this 1 hertz signal we generate the latch enable input exactly after 1 second. So, that whatever the count value available here will be latched after 1 second and after that the counter is reset for next operation. So, this way we can count a frequency of unknown signal. It is better understood by the timing diagram of frequency measurement. Here we see this is a TBO means time base output signal which is 1 hertz actually, but on period is 0.5 second, off period is 0.5 second, total period is 1 second. So, this is 1 cycle, this is 1 cycle and in 1 cycle on is 0.5 second, off is 0.5 second, but we require on to be 1 second for frequency measurement. That is why flip-off is connected at the output of TBO and this flip-off output will be now exactly 1 second delay. That means the signal will be high exactly for 1 second. So, one of the input of AND gate will be high for 1 second and unknown frequency is given to another input of AND gate which is passed to this. So, what this counter will count is number of these unknown frequency pulses for 1 second. So, what we get is frequency in hertz at the end of 1 second. That is why this latch enable signal is activated at the end of 1 second. After latching the data, the counter is prepared for the next measurement cycle by resetting the counter after the data is latched. So, after latch enable is made active, after that immediately reset is also activated which is necessary for next measurement cycle. So, here we have a question, what value flip-off divides the frequency? You pause the video and answer the question. The question was by what value the flip-off divides the input frequency? Naturally, the flip-off is a toggle flip-off is used and whenever there is a transition either positive transition or negative transition at this if the flip-off is negative h triggered at every negative h transition there will be a change in the output. So, the output frequency will be half of the input frequency if it is passed through the flip-off. Now, let us see the time base and counter control signal generation. Here for this we are using JK flip-off here. This is a JK flip-off IC7476. Then another 274C221 these are the monostable multivibrators. Two monostable multivibrators we need one for the latch enable output and another for the reset output. So, here from TBO we get a clock that is applied here. So, at the output what we get is a 0.5 hertz signal that signal is given to the as usual to the one of the input of AND gate and another input of AND gate is connected to unknown frequency after input interface. Then it is given to the X input. X input means the clock input of the 74C926. Now, here it is very important that how we generate the counter control signals one second pulse is over for negative h transition this come high and it will remain high for some time which is based on registers and capacitors used for designing this monostable multivibrator. So, at the Y output we get a latch enable control signal and after this time period is over. So, as soon as this becomes low to high this monostable multivibrator starts is counting and we get here Z output for some predetermined time high depends upon the registers and capacitors used in this network. References here electronic system designed by Vivo T. Tarate Electrotech Publication Satara this is the book used for reference and another website is used for preparing this is this one. Thank you very much.