Circuit to Control 3 Seven Segment Displays using Arduino and 7490 (Part 1 of 9)
A lot of circuits are there to control seven segment displays. Main factor to be considered while designing those circuits is to use minimum number of control pins to control maximum number of seven segment displays. We had already seen a circuit for controlling two common cathode seven segment displays using arduino mega, 7490 and 4511 in previous blogs. A simple circuit for Controlling 3 common cathode seven segment displays, using 4 control pins from arduino mega, is shown below. Circuit has three common cathode seven segment displays, three 4511 ICs, a 7490 IC and an arduino mega as shown in the following diagram.
Complete the circuit. Ground terminal of external voltage source and ground pin of arduino should be interconnected.
Pin out diagram of 7490
Working of 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.
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.