Learn Digital Logic Gates Operation

The Gate is a digital component that is used to compute an output for certain inputs, the inputs and outputs have two states high-1 and low- 0. Let us assume high is 5V and low is 0V (like in CMOS). On a high level the LED will light up and on a low level the LED is off. Now let us see what Logic means.

Learn Digital Logic Gates Operation

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Digital Logic Gates

Gates are what make many of ICs, the two popular families are the 40xx CMOS and the 74xx TTL . Now 40xx come in 74HCT40xx flavors which approach the quality of an ideal gate. Entire circuits with Gates can also be also be burnt into PLDs, FPGAs and CPLDs just like you burn your CDROM. Gates can also be implemented in assembly language which a microcontroller like 8051 will understand and execute.

Hardware gate circuit will operate in real time, nano seconds delay will be there due to propagation delay, gate capacitance and FET switching times etc. Software or microcontroller gates code working will depend on both propagation delay and the CPU clock speed.

Gates can be combined to make combinational or sequential logic circuits. combinational circuits are a complex network of gates interconnected to evaluate a pattern of output for patterns of input. Sequential circuits use memory elements hence output patterns depend both on input patterns and the memory of history of events. An example of combinational logic circuit is a seven segment display decoder CD4511 and and example for a sequential logic circuit is CD4029 up-down counter.

The CD40xx CMOS family can work at even 3V-9V-12V DC and consume low power. The speed is not as fast as 74xx TTL family. It is good for simple portable battery powered circuits. The 74HCTxx series is good for low power and high speed but will work at 5V. When you have problems interfacing CMOS and TTL use 74HCTxx family.

LED Running lights CD4017

This is a Gadget Tutorial for this Article LED Running lights CD4017 – Live Gadget Page.

Red Button Powers LED Running Lights, 555 Clock is counted by CD4017. Adjust R2, See ToolTips. This Demo shows LM555 running a CD4017 Counter to drive Ten Leds sequentially.

Press the Red button below to turn on the circuit press it again to turn off, i have put a new battery and did the wiring for you. The Red LED will flash according to the state of the 555 output at pin 3. The decade counter-divider CD4017 has 10 outputs, for every low to high transition, rising edge, the counter advances one LED. After going one full circle the the first LED lights again and it goes on…..

LED Running lights CD4017

The 10 outputs have 10 green LEDs. The current thru the LED is limited by R1, the current can be calculated like this (9V – 1.6V) / 1K = 7.4mA this is within 20mA which is the danger limit of the CMOS output. You want it to be bright use transistors for every output.


Basic Analog for Digital Designers

“There is a long gap between engineering college and mid career in a non-engineering position, but technology marches on so a simple method of keeping abreast with the latest developments is required. This application note starts with an overview of the basic laws of physics, progresses through circuits 1 and 2, and explains op amp operation through the use of feedback principles.”

Basic Analog for Digital Designers – Application Note

Basic Analog for Digital Designers

AN9510.2 October 19, 2004 – This is an Analog Reference for the Embedded Engineer. An Application Note from Intersil Tech Reference.

  1. Basic Physics Laws, Circuit Theorems and Analysis
  2. Ohm’s and Kirchoff’s Laws
  3. Voltage and Current Dividers
  4. Thevenin’s and Norton’s Theorems
  5. Networks in the Feedback Path
  6. Types of Opamp Configurations
  7. Video Amplifiers


Some algebra, the basic laws of physics, and the basic circuit laws are adequate to gain an understanding of op amp circuits. By applying these tools to various circuit configurations it is possible to predict performance. Further in-depth knowledge is required to do op amp design, and there are many sources where this knowledge can be obtained. Don’t hesitate to try some of these tricks on your local circuit design engineer, but be aware that it may result in a long lecture about circuit design.

Electronic Product Production

a. PCB Assembly.

First Inspect PCB for hairline shorts and cuts and also traces of unwanted copper in the edges and repair them. Also Check if all Drill holes & Slots are proper size and PCB is Fitting in its Place properly, This is because Drilling and Filing should not be done after assembly as it causes serious reliability problems.

Second populate all the resistors, Jumpers, Diodes and Ceramic Capacitors these are tough components. Then Insert all Transistors, LEDs, Displays, Electrolytic Capacitors and IC s (Bases), Here care should be taken not to overheat any component as it may damage them. Lastly Solder Connectors, Relays, Coils and Transformers which may require a high wattage Iron, and Mechanical Reinforcements.

Electronic Product Production

b. Precautions during Production.

  • Observe Polarity for Diodes, El-caps, Connectors, etc.
  • Make sure of Pin 1 for IC s, Regulators, Transistors and Mosfets before insertion.
  • Avoid bases for ICs in production as these fail on use.
  • Make use of Electrostatic protection for CMOS devices.
  • When Cutting Leads use protective Goggles and do it in a separate place as the cut leads fly all over the place.
  • Use Iso Propyl Alcohol (IPA) as de-greasing agent on PCB.
  • Water & Detergent wash is very good but only if coils, Transformers, Relays are hermetically sealed- Impregnated.

Use a Lacquer-Varnish or RTV rubber coat on both sides of PCB including on the components to prevent corrosion and also it helps maintain accuracy-precision.

Lead is a kind of poison, use gloves or wash hands with soap after work is over. Flux, IPA, Thinner Fumes can cause respiratory health problems. Work in a ventilated area use Exhaust Fans and Open Windows. Dispose of Metal, Plastic and Chemical waste separately and well packed as these can contaminate the environment and also cause Injury.

Published online around – Nov 1999