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Shop/Components & Parts/IC’s/74 SERIES/74LS48 BCD to 7-segment Decoder Driver IC. The integrated TTL (74LS48) is a BCD decoder/driver to seven segments common cathode display. Lamp test (LT\) of these types may be performed at any time when the BI\/RBO\ node is at a high. QEA. ACTIVE. CDIP. J. 1. TBD. A N / A for Pkg Type. to QE. A. SNJAJ. QFA. ACTIVE. CFP. W. 74LS48, 74LS48 Datasheet, 74LS48 pdf, buy 74LS48, 74LS48 BCD to 7- Segment Decoder.

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What is the purpose of a seven-segment decoder circuit? A special decoder circuit is needed to translate 4-bit BCD codes into the particular combinations of segment activations that represent decimal digits.

Is there just one 4748, or are there different types of seven-segment displays? Be sure to ask your students to reveal the decoder datasheets they found. Once again, manufacturer datasheets contain a wealth of information, and your students will learn much by researching them.

Learning to analyze digital circuits requires datashete study and practice. Typically, students practice by working through lots of sample problems and checking their answers against those provided by the textbook or the instructor.

While this is good, there is a much better way. For successful circuit-building exercises, follow these steps:. Always be sure that the power supply voltage levels are within specification for the decodificzdor circuits you plan to use. If TTL, the power supply must be a 5-volt regulated supply, adjusted to a value as close to 5. One way you can save time and reduce the possibility of deocdificador is to begin with a datasheet simple circuit and incrementally add components to increase its complexity after each analysis, rather than building a whole new circuit for each practice problem.

Another time-saving technique is to re-use the same components in a variety of different circuit configurations. It has been my experience that students require much practice with circuit analysis to become proficient.

To this end, instructors usually provide their students with lots of practice problems to work through, and provide answers for students to check their work against. While this approach makes students proficient in circuit theory, it fails to fully educate them.

BCD to 7-Segment Decoder and Driver (For Common Cathode)

They also need real, hands-on practice building circuits and using test equipment. So, Decodficador suggest the following alternative approach: Another reason for following this method of practice is to teach students scientific method: Datashwet will also develop real troubleshooting skills as they occasionally make circuit construction errors.

Discuss these issues with your students in the same Socratic manner you would normally discuss the worksheet questions, rather than simply telling them what they should and should not do. I never cease to be amazed at how poorly students grasp eecodificador when presented in a typical lecture instructor monologue format! I highly recommend CMOS logic circuitry for at-home experiments, where students may not have access to a 5-volt regulated power supply.

If your students will be working with real circuits, then they should learn on real circuits whenever possible. If your datasjeet is to educate theoretical physicists, then stick with abstract analysis, by all means!

But most of us plan for our students to do something in the real world with the education we give them.

In most sciences, realistic experiments are much more difficult and expensive to set up than electrical circuits. Nuclear physics, biology, geology, and chemistry professors would just love to be able to have their students apply advanced mathematics to real experiments posing no safety hazard and costing less than a textbook.

Exploit the convenience inherent to your science, and get those students of yours practicing their math on lots of real circuits! A seven segment decoder is a digital circuit designed to drive a very common type of digital display device: The behavior of the display driver IC may be represented by a truth table with seven outputs: A real-life example such as this provides an excellent showcase for techniques such as Karnaugh mapping.


Note that six of the cells are blank because the truth table does not list all the possible input combinations with four variables A, B, C, and D.

Which of these two approaches do you suppose would yield the simplest gate circuitry overall? One of the points of this question is for students to realize that bigger groups are better, in that they yield simpler SOP terms. Truth be known, I chose a pretty bad example to try to make an SOP expression from, since there are only two non-zero output conditions out of ten! This shows a very practical example of SOP and POS Boolean forms, and why simplification is necessary to reduce the number of required gates to a practical minimum.

Be prepared to show your sources when answering this question in class. Liquid crystal display LCD elements require the application of AC voltage rather than DC voltage to prevent certain undesirable effects. Indeed, it just so happens that Exclusive-OR gates do the trick quite nicely:.

Determine what sort of voltage exists across the liquid crystal fluid with the switch in the open position as well as the closed position, and from this determine which switch position results in a darkened LCD versus a transparent LCD. Note that I did not specify anywhere in the question or in the answer whether the application of voltage across an LCD segment darkened or lightened that segment.

This is a detail I leave up to students to research! Describe what this feature is, and why it is used. The answer I give here is purposefully vague, as usual.

What I want students to do is research datasheets on their own and be able to show where they got their information. It is usually necessary to have more than one display digit for a digital system. The most obvious and direct way of driving multiple 7-segment display units is to use an equal number of BCD-tosegment decoders like this:.

Digital Display Circuits

In this particular case, with three 7-segment displays, we would need to use twelve output pins on the microcontroller for the three BCD numbers:. But if each digit requires four output lines for the BCD number, how can we possibly use less than twelve output lines on the processor? One clever way to do just this exploits persistence of human visionby driving only one digit at datasneet time.

Clever techniques such as this are often necessary to make the most of limited hardware. See if any of your students are able to catch this omission!

Digital computers communicate with external devices through ports: These terminals may be set to high or low logic states by writing a program for the computer that sends a numerical value to the port. For example, here is an illustration of a microcontroller being instructed to send the hexadecimal number 2B to port A and A9 to port B:.

Suppose we wished to use the first seven bits of each port pins 0 through datashwet to drive two 7-segment, common-cathode displays, rather than use BCD-tosegment decoder ICs:. The root of this question is little more than binary-to-hexadecimal conversion, but it also introduces students to the concept of controlling bit states in microcomputer ports by writing hex values. As such, this question is very decodificafor There are many applications other than this where you need to get the microcontroller to output a certain combination of high and low states, and the fastest way to program this is to output hex values to the ports.

In case students ask, let them know that a dollar sign prefix is sometimes used to denote a hexadecimal number.

Other times, the prefix 0x is used e. The MM high-voltage display driver IC from National Semiconductor serves as an interface between either a microprocessor or microcontroller and a high-voltage vacuum fluorescent VF display panel. When combined with a similar driver driving the anodes of the same VF display, individual pixels or combinations of pixels may be controlled lit.


An interesting feature of this IC is that it receives the 20 bits of data serially one at a timethrough a single input pin:. Read the datasheet for this device, then comment on why you think a serial rather than parallel data input format was chosen. Also describe the sequence of operation for loading data into this IC and outputting that data to the 20 output lines. If it were not for the serial input, this IC would have quite a few more pins! The timing diagram and description in the datasheet should provide plenty of information for determining how to send data to the display using this IC.

While this question introduces the concept of a vacuum-fluorescent VF display, it also serves as a review of shift register and latch technology. The block diagram should be informative enough for most students to be able to figure out at least an approximate procedure for loading and outputting data. It is interesting to note and discuss with your students that this IC does not decode characters. It merely conditions and outputs bits of information to the grids of a VF display.

One new technology entering the market is organic light-emitting diodesor OLEDs. Describe what these are, and why they hold so much promise for electronic display device elements. But for now Maythey are worthy of their own question in the Socratic Electronics project!

Both students connect their ICs to common-cathode 7-segment displays as such:.

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The student using the notices decodificqdor LED segments glowing faintly, but the patterns are not correct for the digits that are supposed to be displayed. The student using the has an even worse problem: Both have checked and re-checked their wiring, to no avail. It seems as though all the connections are in the right place.

Neither the nor the are designed to source current to the LED segments, only sink current. This question provides an excellent opportunity to discuss the difference between sourcing and sinking current, as well as the importance of knowing what the output stage of an IC looks like internally. An obsolete display technology that still finds enthusiastic followers decldificador the hobbyist world, called Nixie tubesrelies on a BCD-to decoder to drive one of ten different metal decodificavor inside a neon-filled glass bulb.

The tube receives power through a common anode usually over volts DC. A friend of yours is trying to build his own Nixie tube display circuit, but is experiencing problems.

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He wants to use a BCD-to decoder to drive ten discrete transistors, each one handling the current for a digit datashset the datsheet. Being cautious, your friend decides to connect just one of the Nixie tube digits to a transistor, and then to theto see if the idea works before connecting all ten.

Unfortunately, that one digit begins to glow the moment the high-voltage DC supply is turned on, even before the chip receives power! And after that, the gets warm to the touch, which is not good. Thinking he has damaged the IC, your friend turns to you for advice. Did he do anything wrong here? Explain what advice you would give datssheet him. The transistor is not correct. Your friend will have to have a different transistor output stage for his display circuit!

Was this a good idea? Why or why not? Did doing this save the from further damage? I have left the answer purposefully vague so that students will have to figure out how to properly use BJTs to drive the Nixie tube cathodes.