DIGITAL LOGIC PROBE SUBJECT: DIGITAL LOGIC DESIGN

SUBMITTED BY:

HAIDER ABBAS ROLL# 2010-EE-293TAUQIR-UL-ISLAM ROLL#2010-EE-309

SUBMITTED TO:

SIR UMAR KHANSIR SYED UNIVERSITY OF ENGINEERING

& TECHNOLOGY KARACHIDEPARTMENT OF ELECTRONICS ENGINEENG

Writing our first project report in digital logic design, the report was spiritual experience Bringing closure to our five months of effort on the digital logic design. This report provided an outlook for our opinions about this project .This report is different .It presents a balanced, objective and comprehensive view of logic design .The success of this report is not due to any single person, but to the combined successes and failings of a group member .we respect for what that team accomplished grows with each passing day and each class of DLD.

The internet is a strange place to work. For this report we spent 5 hours working closely .we work hard for this project report. our main goal was include complete detail of logic probe design .To avoid presenting a single biased view about how to write a project report.

We are very thankful to Sir UMAR KHAN because due to his hard working we are able to design a project in DIGITAL LOGIC DESIGN .Thanks also go to sir Omar khan ,who looks out for our best. He diligently read and comments on every page of this report.

HAIDER ABBAS &

TAUQIR UL ISLAM

Digital logic is concerned with the interconnection among digital components and modules and is term used to denote the design and analysis of digital system .The best known example of a digital system is the general purpose digital computer. This report presents the basic concepts used in the design of logic probe .It provides various methods and techniques suitable for a variety of logic probe applications and construction. It covers all aspects of digital logic probe design from the electronic gate circuits to the complex structure.

The components used to construct digital logic probe are manufactured in integrated circuit form. Integrated circuits contain a large amount of interconnected digital circuits within a single small package. The report is suitable for a design of logic probe and description of every component used in this project and also detail of require elements circuit diagram.

We wish to express our thanks to Sir Omar Khan for pointing out corrections and help in project designing. My great thanks go to my senior friends for all the suggestions, their encouragements and their support during the preparation of this project report.

HAIDER ABBAS &

TAUQIR UL ISLAM

Serial NO. TOPICS PAGE NO.

1- PROJECT DESCRIPTION 1

2- LIST OF COMPONENTS4

3- WORKING PHENOMENA5

4- LOGIC DIAGRM6

5- COMPONENT BILLING7

6- PROJECT MEMBER ROLE8

7- REFERENCE9

LOGIC PROBE:

The purpose of a logic probe is to examine the logic states at a particular point in an electronic circuit. It is usually used in fault finding and testing but it can also be used t assist in electronic design. There are many circuits for logic probes. Some are very simple while others have added so many features the probe has become too big. At a minimum any logic probe should be usable with both CMOS and TTL logic families. In this design a pulse detection circuit has been added because the detection of electronic pulses

is so important today in many electronic circuits. The kit is constructed on a single-sided printed circuit board (PCB). Protel Autotrax and Schematic were used.

CIRCUIT DESCRIPTION:

There are two main logic families used in

electronics: CMOS and TTL. For CMOS the supply

voltage may be anywhere between 3V and 15V and the

logic levels used are taken as a proportion of the supply

voltage. Levels quoted by different manufacturers vary so

the the probe should be calibrated for the most extreme

cases.) For CMOS the extreme limits are:

HIGH greater than 73.3% of supply voltage

LOW less than 26.6% of supply voltage

For TTL the supply voltage should be 5 volts and the logic

Levels are:

HIGH greater than 2 volts

LOW less than 0.8 volts

COMPONENTS DESCRIPTION:

1-SEVEN- SEGMENT DISPLAY:

One common requirement for many different digital devices is a visual numeric display. Individual LEDs can of course display the binary states of a set of latches or flip-flops. However, we're far more used to thinking and dealing with decimal numbers. To this end, we want a display of some kind that can clearly represent decimal numbers without any requirement of translating binary to decimal or any other format.

This requires just seven LEDs (plus an eighth one for the decimal point, if that is needed). A common technique is to use a shaped piece of translucent plastic to operate as a specialized optical fiber, to distribute the light from the LED evenly over a fixed bar shape. The seven bars are laid out as a squared-off figure "8". The result is known as a seven-segment LED.

We've all seen seven-segment displays in a wide range of applications. Clocks, watches, digital instruments, and many household appliances already have such displays. In this experiment, we'll look at what they are and how they can display any of the ten decimal digits 0-9 on demand.

Seven-Segment Display Layout

The illustration to the right shows the basic layout of the segments in a seven-segment display. The segments themselves are identified with lower-case letters "a" through "g," with segment "a" at the top and then counting clockwise. Segment "g" is the center bar.As shown in the two schematic diagrams above, the LEDs in a seven-segment display are not isolated from each other. Rather, either all of the cathodes, or all of the anodes, are connected together into a common lead, while the other end of

2-DIODE:

Diode is a unidirectional component, it allows passing a Signal in one direction and blocks it in another direction. when it is forward biased it allows the signal to pass through it and it blocks that signal if it is reversed biased. it is used as a switch. Different diodes are used for different purposes. However, the basic working of a diode still remains the same allows current to flow only in one direction. Here, in this article, I will try to explain you how does a diode work?

. It is a p-n junction semiconductor

Applications of DiodesAs already mentioned, all diodes are not used for the same purpose, though the basic function of a diode is the same. It allows the flow of current in only one direction. Varactor diode is used in places where they need to solve the purpose of a variable capacitor. Tunnel diode is used in applications where we need the current to increase and decrease alternately. The application of LED lights is known to all. LEDs compulsorily need to operate in the forward biased mode. Zener diode, on the other hand is operated in the reverse biased mode and is

3-BC548 TRANSISTOR:

The BC548 is a general purpose silicon NPN BJT transistor found commonly in European electronic equipment; the part number is assigned by Pro Electron, which allows many manufacturers to offer

electrically and physically interchangeable parts under one identification. The BC548 is commonly available in European Union and Commonwealth Countries and is often the first type of bipolar transistor young hobbyists encounter. The BC548 is often featured in circuit diagrams and designs published in Electronics Magazines such as "Silicon Chip" and "Elektor".

As a representative of the large family of bipolar transistors the BC548 provides a "stepping off point" to the use of more esoteric, higher voltage, current or frequency devices for beginners.

IC7400 : The output is high when either of inputs A or B is high, or if neither is high. In other words, it is normally high, going low only if both 7400 series

The 7400 chip, containing four NANDs. The second line of smaller numbers (7645) is a date code; this chip was manufactured in the 45th week of 1976. The N suffix on the part number is a vendor-specific code indicating PDIP packaging.

The 7400 series of transistor-transistor logic (TTL) integrated circuits are historically important as the

first widespread family of TTL integrated circuit logic.[1][2] It was used to build the mini and mainframe

computers of the 1960s and 1970s. Several generations of pin-compatible descendants of the original

family have since been de-facto standard components.

S.NO NAME OF COMPONENTS

1- 7400 IC

2- BC548 TRANSISTOR

3- Five 370Ω,1 KΩ & 10 KΩ RESISTORS

4- FOUR DIODES

5- SEVEN-SEGMENT DISPLY

6 PCB BOARD

7- JUMPER WIRES

A logic probe is a hand-held pen-like test probe used for analyzing and troubleshooting the logical states (Boolean 0 or 1) of a digital circuit. While most are powered by the circuit under test, some devices use batteries. They can be used on either TTL (transistor-transistor logic) or CMOS (complementary metallic oxide semiconductor) integrated circuit devices.

There are usually three differently-colored LEDs on the probe's body:

Red and green LEDs indicate high and low states respectively

An amber LED indicates a pulse

The pulse-detecting electronics usually has a pulse-stretcher circuit so that even very short pulses become

visible on the amber LED. A control on the logic probe allows either the capture and storage of a single

event or continuous running.

When the logic probe is either connected to an invalid logic level (a fault condition or a tri-statedoutput)

or not connected at all, none of the LEDs lights up.

Another control on the logic probe allow selection of either TTL or CMOS family logic. This is required

as these families have different thresholds for VIH and VIL.

Some logic probes have a separate audible tone for each of the logical states. An oscillating signal causes

the probe to alternate between high-state and low-state tones.

A logic probe is a cheap, versatile and convenient digital test instrument, but can test only a single signal

at a time. When many logic levels need to be observed or recorded simultaneously, a logic analyzer is

used.

Pulse Detector. This circuit consists of 4 CMOS inverters (in the 4049/14049) andsome passive components. Start at pin 7. Usually R15 holds pin 5 low which makes pin 4 high, which in turn

makes pin 7 high via diode D4 leakage. If pin 7 is pulled down by a negative pulse from C2 or C3 the pulse travels through the first inverter (and becomes high), then to C4 and the second inverter to arrive at pin 4 as a low. The low holds pin 7 low via diode D4. Pin 6 is now high. Pin 5 is therefore held high until C4 discharges through R15. When pin 5 falls to the CMOS low level pin 4 goes high again and the latch is released. The pulse indication time is set by the time constant C4.R15. When a pulse is detected

it is stretched to about a second during which time the

change into a sharp pulse and put out signals at rail voltage. Any change of level (low to high or high to low) at the probe will cause one inverter to go high and the other to go low. By adding the diodes D2 and D3, when a level change occurs the output going from low to high is blocked temporarily until its leakage current charges the 100pF series capacitor. However, the output going from high to low is not blocked because its diode is then forward biased and a negative going pulse arrives at pin 7. As describes in the previous paragraph a negative pulse at pin 7 causes a pulse detection signal. If the input to the logic probe is not in a defined state (that is, if it is in the range 26.6% to 73.3% of the supply voltage for a cmos

circuit, or 16% to 40% of the supply voltage for a TTL circuit) then it is in the floating level. However, the cmos gate connected to the probe will still recognise the input as high or low. Normally it will switch at 50% so normally we could call 26.6% to 50% of the supply voltage

floating low, and 50% to 73.3% floating high. The implications of this are: that pulses to and from the floating range will only be that TTL pulses to marginal positive levels may not be detected by the pulse detector (but will still show up on the level detectors if they are not too fast) that the pulse detectors will show what users usually want to know, namely whether any transients are going to cause switching in cmos devices If the probe is floating (that is have an undetermined input) then it will be floating either high or low. If it is floating high then it will not detect a positive going pulse because it is not a true pulse as far as the probe is concerned. Similarly, if it floating low then it will not detect a negative pulse. All these conditions are illustrated in the table and diagrams.

.WHAT TO DO IF IT DOES NOT WORK?Poor soldering is the most likely reason that the circuit does not work. Check all solder joints carefully under a good light. Next check that all components are in their correct position on the PCB. Check the IC's, the PUT, diode and LED orientations. The piezo leads and all capacitors may be connected either way to their pads.

TESTING CIRCUITS WITH THE LOGIC PROBEThe Logic Probe can also be used to test all types of circuits, providing the waveform has an amplitude of at least 5v. In general, if the signal in a circuit will trigger a microcontroller, it will also be large enough to be detected by this Logic Probe. Before using the Logic Probe for the first time, you must be sure it is operating correctly. The 5x7 Display Project provides an ideal project to test the operation of the "Probe."Some of the lines of the micro in the 5x7 are turning on and off at a fairly fast rate. Pins 6 to 12 drive the anodes of the LED display and these are active when the display is illuminating. Probing these lines will activate both the HIGH and LOW LEDs on the "Probe." The clock line to the "shift-chip - a 4017" (pin 17) is activated for a very short period of time and is low for a very long period of time (in computer terms) and the HIGH LED on the "Probe" will glow fairly dull while the green LED will be very bright. A faint beep will be heard from the piezo along with the high tone. A very brief pulse can be detected on the reset line to the 4017 (pin 18) and this will prove the Logic Probe is capable of detecting a glitch or pulse. When the Logic Probe has been tested for performance, it is ready for testing "unknown" circuits.

S.NO NAME OF COMPONENT PRICE

1-BC548 TRANSISTOR

10 .OO

2-7400 IC

10.00

3-SEVEN –SEGMENT DISPLAY

12.00

47 RESISTOR

12.00

5-4 DIODES

8.00

6-JUMPER WIRES

10.00

7-CIRCUIT BOARD

20.00

The success of this project is not due to any single person, but to the combined successes and failings of a group member’s .we respect for what that team accomplished grows with each passing day and each class of DLD.

The internet is a strange place to work. For this project we spent 5 hours working closely .we work hard for this project. Our main goal was include complete detail of logic probe design .To avoid presenting a single biased view about how to write a project report.

Making our first project in digital logic design, the project was spiritual experience Bringing closure to our five months of effort on the digital logic design. This report provided an outlook for our opinions about this project .This report is different .It presents a balanced, objective and comprehensive view of logic design.

This project has been making by the combined efforts and skills of project members. We think that we have accomplished what we set out to , and what was to further improve this project and make it even more

8- BREAD BOARD120.00

useful for work. We contributed a great amount of time ,talent, and effort to useful this project .

1- http://kitsrus.comKIT 24. LOGIC PROBE

2-Email at peter@kitsrus.com if we have any problem

3-WWW.wikipedia .com

4-www.mycircuit.com

5-www.circuitstoday.com

6-www.electroniclab.com