DESIGN AND TESTING OF A SEVEN SEGMENT DECODER Randy Dimmett. Input to display the characters 1-9 and a-f on a seven-segment display. The design was done on Mentor’s design software and simulated to make sure the. In this experiment a seven-segment display was successfully designed. Nov 15, 2010  Introduction Seven segment LED displays are often found in clock radios, VCRs, microwave ovens, toys and many other household items. They are primarily used to display decimal numbers but they can also display a few alphabets and other characters. This experiment describes interfacing a seven segment LED display to a PIC16F688 microcontroller.

• Design Of Seven Segment Display Driver For Bcd Codes Experiment For Kids
• Design Of Seven Segment Display Driver For Bcd Codes Experiment 1
• Design Of Seven Segment Display Driver For Bcd Codes Experiment

7-Segment Decoder Driver and Display Lab: 9 7-Segment Decoder Driver and Display and the Basic Memory Unit Introduction In this experiment you will demonstrate the operation of a decoder-driver circuit that accepts a binary or BCD input code and generates the 7 segment display signals to produce the numbers 0 through 9 and other characters. Figure 1 shows a simplified block of the 74LS48 BCD to 7-Segment Decoder.

Design Of Seven Segment Display Driver For Bcd Codes Experiment For Kids

The 74LS48 contains three main block circuits, a 7-segment decoder, a driver and a system of basic memory units. The basic memory unit is often called a latch or a flip-flop. The decoder outputs drive an encoder circuit made up of OR gates that generate the 7-segment code necessary to display the digits 0 through 9 and the letters a through f.

The output devices are current driver transistors that supply the proper current to th e segments in the driver. Figure 1 Equipment needed Microprocessor power supply Logic Probe 74LS00 74LS02 74LS04 74LS48 (46) 7-Segment LED Figure 2 Part 1. Set-Reset flip-flop. Wire the latch circuit shown in fiqure 2. The Set (A) and Reset (B) are the inputs and C (L1) and C (L2) are the outputs.

Apply power to the circuit and create a truth table for S and R Inputs and C and C outputs. Wire the latch circuit shown in figure 3. Repeat steps 1. For circuit 3. These new outputs are labeled D and D.

Why do we call this circuit a basic memory unit? What happens to the outputs when S and R both 0? Refer to the textbook (Katz) for a discussion of flip-flops (chapter 6). (7-Segment Decoder-Driver and Display). Construct the circuit shown in figure 4.

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Use the TTL handbook to verify the correct conections. The pin connections for the 74LS48 and the 7-Segment Display are shown in fiqure 5. Calculate the value of the resistor between the 74LS48 and the 7-seg LED.

Apply power to the circuit. Create a truth table for figure 4. Do the LEDs L1-L4 which output the binary word agree with the output of the 7-Segment LED? What does the 7-Segment LED read in binary states 1010-1111? What do you think the LT, RBI and BI/ RBO pins do? Figure 3 Figure 4 Figure 5 Check the documentation.

However to display the characters and numbers (in order to produce the decimal readout), seven-segment displays are most commonly used. Mostly these displays are driven by the output stages of digital ICs (to which the visual indication of the output stages has to be performed) such as latches and decade counters, etc. But these outputs are in the form of 4-bit binary coded decimal (BCD), and not suitable for directly driving the A display decoder is used to convert a BCD or a binary code into a 7 segment code. It generally has 4 input lines and 7 output lines. Here we design a simple display decoder circuit using logic gates. Even though commercial BCD to 7 segment decoders are available, designing a display decoder using logic gates may prove to be beneficial from economical as well as knowledge point of view.

Principle of Display Decoder Circuit The basic idea involves driving a common cathode 7-segment LED display using combinational logic circuit. The logic circuit is designed with 4 inputs and 7 outputs, each representing an input to the display IC. Using Karnough’s map, logic circuitry for each input to the display is designed. Related Post: Theory Behind the Circuit: The first and foremost aspect of this circuit is decoder.

A decoder is a combinational circuit which is used to convert a binary or BCD (Binary Coded Decimal) number to the corresponding decimal number. It can be a simple binary to decimal decoder or a BCD to 7 segment decoder. Another relevant section is the combinational logic circuitry. A combinational logic circuit is a system of logic gates consisting of only outputs and inputs. The output of a combinational logic circuit depends only on the present state of the inputs and nothing else. Best examples of such circuits are Encoders and Decoders, Multiplexers and De-multiplexers, Adders, Subtractors etc.

To understand the design and operation of these logic circuits, one needs to have a good knowledge about Boolean algebra and logic gates. For example few basic Boolean algebra rules to be followed are the complementary law, associative law, De-Morgan’s law etc. A 7 segment LED display consists of an arrangement of 8 LEDs such that either all the anodes are common or cathodes are common. A common cathode 7 segment display consists of 8 pins – 7 input pins labeled from ‘a’ to ‘g’ and 8 th pin as common ground pin. 7 Segment Display Decoder Circuit Design Step 1: The first step of the design involves analysis of the common cathode 7-segment display. A 7-segment display consists of an arrangement of LEDs in an ‘H’ form.

A truth table is constructed with the combination of inputs for each decimal number. For example, decimal number 1 would command a combination of b and c (refer the diagram given below). 7 Segment LED Image Resource Link: www.thelearningpit.com Step 2: The second step involves constructing the truth table listing the 7 display input signals, decimal number and corresponding 4 digit binary numbers.

The truth table for the decoder design depends on the type of 7-segment display. As we mentioned above that for a common cathode seven-segment display, the output of decoder or segment driver must be active high in order to glow the segment. The figure below shows the truth table of a BCD to seven-segment decoder with common cathode display. In the truth table, there are 7 different output columns corresponding to each of the 7 segments. Suppose the column for segment a shows the different combinations for which it is to be illuminated.

Design Of Seven Segment Display Driver For Bcd Codes Experiment 1

So ‘a’ is active for the digits 0, 2, 3, 5, 6, 7, 8 and 9. From the above truth table, the Boolean expressions of each output functions can be written as a = F1 (A, B, C, D) = ∑m (0, 2, 3, 5, 7, 8, 9) b = F2 (A, B, C, D) = ∑m (0, 1, 2, 3, 4, 7, 8, 9) c = F3 (A, B, C, D) = ∑m (0, 1, 3, 4, 5, 6, 7, 8, 9) d = F4 (A, B, C, D) = ∑m (0, 2, 3, 5, 6, 8) e = F5 (A, B, C, D) = ∑m (0, 2, 6, 8) f = F6 (A, B, C, D) = ∑m (0, 4, 5, 6, 8, 9) g = F7 (A, B, C, D) = ∑m (2, 3, 4, 5, 6, 8, 9) Step 3: The third step involves constructing the Karnough’s map for each output term and then simplifying them to obtain a logic combination of inputs for each output. K-Map Simplification The below figures shows the k-map simplification for the common cathode seven-segment decoder in order to design the combinational circuit.

From the above simplification, we get the output values as Step 4: The final step involves drawing a combinational logic circuit for each output signal. Once the task was accomplished, a combinational logic circuit can be drawn using 4 inputs (A,B,C,D)and a 7- segment display (a,b,c,d,e,f,g) as output. Display Decoder Circuit Operation The circuit operation can be understood through the truth table itself. When all the inputs are connected to low logic, the output of the combinational logic circuit would be so as to drive all the output LEDs except ‘g’ to conduction. Thus the number 0 will be displayed. Similar operation would take place for all other combinations of the input switches.

Note: Also read the interesting post – Practically BCD to 7 segment decoders are available in form of integrated circuits such as 74LS47. Apart from regular 4 input pins and 7 output pins, it consists of a lamping test pin used for segment testing, ripple blanking input pin used to blank off zeros in multiple display systems, ripple blanking output pin used for cascading purposes and a blanking input pin. Applications of Display Decoder Circuit. This circuit can be modified using timers and counters to display the number of clock pulses.

This circuit can be modified to develop an alphabet display system instead of a decimal number display system. It can be used as a timer circuit. Also Read:  Limitations of Display Decoder Circuit.

Design Of Seven Segment Display Driver For Bcd Codes Experiment

This circuit involves lot of logic gates and is quite complex. Timing delay by each logic gate is a matter of concern and this circuit might not produce accurate results when used to display count of pulses.

This is a theoretical circuit and may require few modifications.