Showing posts with label Ultiboard. Show all posts
Showing posts with label Ultiboard. Show all posts

Saturday, December 19, 2015

Multisim| Stopwatch Timer Cascading 7 Segments 74ls190 74ls47

Stopwatch Timer Cascading 7 Segment Displays

Written by Larsha Johnson

In this blog a stopwatch is simulated in Multisim and converted to a PCB layout via Ultiboard

Build of material:

  1. Two 7 segment displays
  2. Resistor packs (100 Ohms) *included in updated model
  3. Two 74ls190 (up/down counters)
  4. Two 74ls47 (BCD decoder)
  5. 555 Timer (1MHz digital clock in Multisim)
  6. One toggle switch (up/down)
  7. 1 Tact push button switch (reset)

You will need: 
Download File

Seven segments are everywhere, clocks, elevators, microwaves, cars, etc.

To connect the 7 segments, match A-G segments to the pins of the decoder according to the datasheet. RI, BI, LT should be connected to VCC.
The 74ls190 can be preset to a specific start time.

Seven segments and decoders are one of the most common types of parts I used to build circuits during my first years studying Computer Engineering Technology. Knowing the difference between anode and cathode use to be a task as well as knowing which type of decoder to use. Now that I have played around with them I am able to build more circuits using the two. 

As a beginner you may want to try this 7 Segment Counter project. In the video you will see how I designed an up/down automatic counter and the list of parts I used. 

Snippet for drag and drop coming soon.
*Visit our Git page for free files.

Thursday, August 20, 2015

Multisim and Ultiboard| 74ls240 wired 3D PCB

74ls240 Wired

Written by Larsha Johnson

Ever wonder what is a buffer and why is it useful? In this blog I will show you how to wire a 74ls240 TTL using NI Multisim and NI Ultiboard and some practical applications. First a few keywords:

  • Buffer = symbol is a triangle and its input is its output. Purpose is to slow current.
  • Octal = eight. The 74ls240 has eight inputs/outputs
  • Tri-state/3-state = allows an output port to assume a high impedance (Z) state in addition to low and high values.
  • Fan out= number of devices that an output is attached to.
A tri-state buffer or inverting buffer looks like a regular buffer or inverter, except there is an additional "enable" control signal entering the gate. When the enable is "1" the buffer is driving the output; when the enable is "0," the output is turned off ("tri-stated"). 

74ls04 vs 74ls240 Ok the 74ls04 takes its input and outputs the opposite i.e. high=low low=high.
The 74ls240 is a bit more complex...kinda. It can also take its input and output the opposite depending on the G pin. This is what makes the 74ls240 different. The output is determined by pins G (1G or 2G) and pin 1A(1-4)/2A(1-4).  
When the G input is high, the output is "Z" and no electrical current flows through no matter if pins 1A(1-4)/2A(1-4) is high/low.

The 74LS240 belongs to 74XXYY IC series. The 74LS240 is a series of octal buffers and line drivers designed specifically to improve both the performance and density of three-state memory address drivers, clock drivers, and bus-oriented receivers and transmitters. The IC has a wide range of working voltage, a wide range of working conditions, and directly interfaces with CMOS, NMOS, and TTL. The output of the IC always comes in TTL which makes it easy to work with other TTL devices and microcontrollers. The IC 74LS240 is smaller in size and it has a much faster speed which makes it reliable in every kind of device.

Wednesday, July 29, 2015

NI Multisim Ultiboard- VBB Diode-Resistor Logic Gates AND & OR

Use Diodes and Resistors to Perform Logic

Date: 7/29/2015

Using NI Multisim I created a simply design to show how to use basic components to create an AND & OR gate. 
Diode logic gates use diodes to perform OR and AND logic functions as shown in the circuit diagram. Connection of the LED at the output is optional which simply displays the logical state of the output, i.e. the logic state of output is 0 or 1, if LED is off or on, respectively. 

Diodes have the property of easily passing an electrical current in one direction, but not the other. Thus, diodes can act as a logical switch. Diode logic gates are very simple and inexpensive, and can be used effectively in limited space. 

However, they cannot be used extensively due to the obvious logic level shift when gates are connected
in series. In addition, they cannot perform a NOT function, so their usefulness is quite limited. This type of logic circuit is rarely found in integrated form. 

OR Gate (74ls32)

If one or both inputs are at logic “1” (5 volts), the current will flow through one or both diodes. This current passes through the resistor and causes the appearance of a voltage across its terminals, thereby obtaining logic “1” on the output. 

Here only a logic “0” (0 volts) on the output when both inputs are in logic “0”. In this case, the diodes do not conduct, there is no current through the resistor R and there is no voltage across its terminals. As a result the voltage at Vout is the same as ground (0 volts)

AND Gate (74ls08)

When both inputs are at logic “1″, the two diodes are reverse biased and there is no current flowing to ground. Therefore the output is logic “1” because there is no voltage drop across the resistor R.

If one of the inputs is logic “0”, the current will flow through the corresponding diode and through the resistor. Thus the diode anode (the output) will be logic “0”.

This method works fine when the circuits are simple, but there are problems when you have to make interconnections with such gates.

Reference material: 

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