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Thursday, 30 October 2014

Circuit to Control a Common Cathode Seven Segment Display using 7490 (Part 1 of 9)

by realfinetime  |  in Seven Segment Display at  10:08

<<<<  Previous : Seven Segment Display + 7490 + 4511 + Press Button Switch

          We had already seen the circuit to control a common cathode seven segment display using 7490 and 4511 through a press button switch in previous blog. Here, we will see the circuit to control a common cathode seven segment display using 4511 and 7490 through an arduino mega. Circuit is done as shown in the following diagram. It is better to read my previous blog which will give you an idea about the working of 7490 and 4511.



Pin out diagram of 7490

          7490 is clearly explained in it's datasheet. It is better to learn the datasheet before using 7490. It is a monolithic counter and contains four master-slave flip-flops and additional gating to provide a divide-by-two counter for which the count cycle length is divide-by-five. Pin out diagram of 7490 is given below.
          From the datasheet, it is clear that, counting will take place, if any of the following conditions is satisfied (Refer Reset / Count Function table in Page 3 of datasheet).

R0(2) and R9(2) are LOW.
R0(1) and R9(1) are LOW.
R0(1) and R9(2) are LOW.
R0(2) and R9(1) are LOW.

          In our circuit, we are grounding R0(2) (pin 3) and R9(1) (pin 6) of 7490 (condition 4). We can design two types of counters using 7490. They are BCD counter and Bi-quinary counter (Refer Function Tables of 7490 given in page 3 of datasheet). Here, we are designing the circuit for BCD counter. 7490 will work in BCD Count mode if, output Qa (Pin 12) of 7490 is connected to the input B (pin 1) of 7490. Clock input is given to the input A (pin 14) of 7490. In our circuit, clock input is given using a press button switch. If all these conditions are met, we will get a BCD counter at the output pins (Qa, Qb, Qc and Qd). Counter will count from 0-9 in each negative transition of clock input.

          7490 provides some options for resetting the IC (Refer Reset / Count Function table in Page 3 of datasheet). Two types of resetting are there. In the first type Qa, Qb, Qc and Qd becomes 0, 0, 0 and 0. In the second type, Qa, Qb, Qc and Qd becomes 1, 0, 0, and 1. Resetting can be done by three methods.

Method 1 : R0(1) - HIGH, R0(2) - HIGH, R9(1) - LOW.
Method 2 : R0(1) - HIGH, R0(2) - HIGH, R9(2) - LOW.
Method 3 : R9(1) - HIGH, R9(2) - HIGH.

Method 1 results in first type of resetting.
Method 2 results in first type of resetting.
Method 3 results in second type of resetting.

After resetting, counting will restart from 0.

Continued in Next Part (Part 2) >>>>

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All the circuits, published in this blog is only after testing and getting proper results in my private lab. When you try these circuits, you should check the supply voltage, polarity of components, presence of childrens nearby and shorts in the circuits. This website will not be responsible for any harm happened to you or your components caused by your carelessness.

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