A couple of very simple frequency counter circuits are shown below and can be easily built by any electronic enthusiast for the intended purpose. The circuit diagram was provided by Mr.Kapital through an order in Fiverr.com, I was asked to explain the functioning by him.
1) Frequency Counter Using IC 74LS47
The first circuit can be understood with the following points:
1. The IC 555 is configured in an astable mutivibrator mode (AMV).
2. AMV is a configuration in which the IC555 generates alternate high and low pulses at its pin number 3.
3. These pulses are simply the generation of positive voltages in succession at a certain rate; say for example 20 positive and negative alternate voltage peaks in one minute. The capacitor and resistor values can be adjusted for adjusting the generated pulse rate.
4. In the circuit the 74LS90and 74LS47 are used for counting the above pulses from the IC555.
5. The IC74LS90 accepts the pulses from the IC555 at its input pin no.14.
6. Its internal circuit converts these pulses in the form of special codes (binary) and fed in a certain sequence to the decoder IC 74LS47 through its output pin no.12,9,8,11.
7. The above codes are accepted by the decoder IC 74LS47 at its input pin nos.7,1,2,6 in the same above sequence.
8. The IC74LS47 now decodes this binary information and illuminates the LED display bars in such a way that it starts displaying the numbers 1 to 9 in response to the pulses generated by the IC555, meaning, the first pulse from the IC555 displays a no.1 over the right hand side display, the next pulse makes it display the number 2, then 3 and so on until the display reaches the number 9.
9. During the above procedure the left hand side display continues to show the number zero.
10. However the moment the right hand side display reaches the number 9, the next pulse overflows from pin 11 of the right IC74LS90 and becomes available to pin 14 of the left IC 74LS90 which now repeats the above procedure.
11. So now the left hand side begins continuing the counting by displaying the numbers 1 to 9 and we witness the ongoing counting with the displays modules together showing the number 11 until the number 99.
12. That's the maximum number of digits the shown counter design can display at the maximum.
13. For making the counter a three digit counter or a four digit counter, simply the above stages may be added in the same pin out sequence as the two modules are connected in the given diagram.
14. The input at the pin 14 of the first module can be replaced with any type of pulse that needs to be monitored or which needs to be counted.
The pins of the ICs which are connected to the positive and the negative points of the power supply are the supply input pins of the respective ICs which require precisely 5 volts for operating.
The resistors R1 to R7 on each display are connected for limiting current to the display LEDs so that a constant illumination is maintained and also for safeguarding the display LEDs from getting damaged.
2) Frequency Counter Circuit Using a Single IC 4033
The next circuit shown below can be used for measuring or counting frequency or Hz. The IC is very simple to make and utilizes just a single IC 4033 and a common cathode display as the main ingredients.
If higher frequencies in the the order of two or three digits are required to be measured, then simple the number of modules can be connected in series as described.The simple frequency counter circuit shown below will effectively convert any pulse at its input into a display over the 7- segment cathode block.The IC has an internal BCd to 7 segment translator which directly converts the pulses at its input to readable numerical bars at the connected display block.
A single IC 4033 is able to handle only one common cathode display block and therefore the shown circuit is able to show numbers from 0 to 9 in response to the relevant clocks applied at its input.
The IC may be easily reset at any point. For example suppose 6 clocks were applied at the input and the the display now reads 6, it can be reverted to zero simply by pressing the shown push button, if needed.
Pin #1 is the input where the clock or the pulses are applied for counting.
In order to make the counter able to count to two digit or 3 digit or 4 digit etc. just include integrate the relevant number of modules as shown in the diagram and connect their outputs in the following manner:
Connect pin #5 of the first module to the clock input of the next module and connect pin #5 of the second module to clock input of the third module and so on.
Make the reset pins common, so that a single push button can be used for resetting all the modules at once.
Supply terminals will also need to be made into common rails.
A capacitor of 0.1uF should be connected close to the supply rail for decoupling purpose.