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Thursday, 30 October 2014

Working of the Circuit to Control a Seven Segment Display, 7490 + 4511 (Part 2 of 9)

by realfinetime  |  in Seven Segment Display at  10:19

<<<<  Read Previous Part (Part 1)

Pin out diagram of 4511

          Datasheet of 4511 is given hereDatasheet must be read before using 4511. 4511 is a BCD to 7-segment latch / decoder / driver with four address inputs (D0-D3), an active low blanking input (BL), a lamp test (LT) and a latch enable (LE).

          From the function table of 4511 given in page 2 of datasheet, it is clear that, when a BCD input is given to 4511 through D0, D1, D2 and D3, we will get a corresponding number displayed in seven segment display. BCD input for 4511 is given from the output pins of 7490 (Qa, Qb, Qc and Qd). LT and BL pins of 4511 should be at HIGH voltage. Similarly LE pin should be at LOW voltage.

Pin out diagram of Common Cathode Seven Segment Display

          Pin out diagram of common cathode seven segment display is given below. There will be only one cathode pin for all the eight anode pins. Segments of the seven segment display is connected to the output pins (Qa - Qg) of 4511. A resistor of 1 K should be connected to the anode pins to protect the segments from high currents.
          Vcc is given from a regulated 5V source. Vcc is given to 7490 as well as 4511. Gnd pin of 7490, 4511 and Common cathode seven segment display is connected to the Gnd pin of voltage source.

Connections of 4511 and 7490 to arduino mega can be summarized as:

* Connect INPUT A (leg 14) of 7490 to 13th digital output of arduino mega.
* Connect R0(1) (leg 2) and R0(2) (leg 3) of 7490 to 12th digital output of arduino mega.
* Connect LE (leg 5) of 4511 to 10th digital output of arduino mega.

* Gnd of arduino mega should be connected to the gnd terminal of voltage source.

Working of Circuit

          We had already seen the circuit for controlling a common cathode seven segment display using 4511 driver in previous blogs. In this circuit, when 10th digital output of arduino is HIGH, LE of 4511 becomes HIGH. This will keep the output (Qa - Qg) of 4511 in previous state, even if the input (D0 - D3) changes. When 10th digital output of arduino is LOW, LE of 4511 becomes LOW. Now, the output (Qa - Qg) of 4511 will change when input (D0 - D3) changes.

         When 12th digital output of arduino is HIGH, R0(1) and R0(2) of 7490 becomes HIGH. This will reset 7490. When 12th digital output of arduino is LOW, R0(1) and R0(2) of 7490 becomes LOW. Now, 7490 will count in all negative transitions of clock_input (INPUT A of 7490).

          When 10th and 12th digital outputs of arduino are LOW, during the negative transitions (HIGH to LOW transition) of  clock input (INPUT A of 7490 IC), 7490 counts. Count will be converted to BCD and is given as input to 4511. 4511 will convert BCD for seven segment display and corresponding number will be displayed in the seven segment display.

Continued in Next Part (Part 3) >>>>

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IMPORTANT NOTICE

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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