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.

Three Point Preset Counter

This is a prototype of a Preset Counter. It is built with ICM7217. The cabinet is ABS Plastic DIN 96-96. The Panel is Engraved on Acrylic.

I don’t remember for which application it was used. It has three thumbwheel settings, when the proximity switch counts upto the set-value, the corresponding relay turns ON, with a State Indicating LED on front panel.

Three Point Preset Counter

These can be configured sequentially or to work synchronously, this depends on what customer wants. Both modes may give the same result. In sequential operation, Some of these counters-timers may need to wait for an external trigger or feedback from a limit switch or another process like pressure alarm. Then more Input options may have to be provided.

Basic Electronic Digital Circuits

Counters, timers, analog-process and its interconnectivity makes up the various process loops or chain-reactions in Machine control. The various types of sensors for measurement and feedback of analog and event parameters, monitor the mechanical system and communicate the data to the process instruments.

The below circuit is a reference, i used the old intersil hot ideas book. There was no internet then. Databooks were valuable reference material. In the below timer circuit replace the clock with a schmitt trigger signal conditioning, it becomes a event counter or preset counter with thumbwheel input. See photograph above.

ICM7217 Timer and Counter

The Actuators like Drives, Solenoids, Pumps, Valves and Heaters act in accordance to the commands of the control system. This regulates and manages the process or machine to deliver consistent and repeatable yield of the end product.

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.

 

CD4093 Quad NAND Schmitt Trigger

The CD4093B consists of four Schmitt-trigger circuits. Each circuit functions as a 2-input NAND gate with Schmitt-trigger action on both inputs. The gate switches at different points for positive and negative-going signals.

CD4093 – Quad 2-Input NAND Schmitt Trigger

The difference be-tween the positive (VTa) and the negative voltage (VTb)isdefined as hysteresis voltage (VH). All outputs have equal source and sink currents and con-form to standard B-series output drive.

CD4093 Quad NAND Schmitt Trigger

CD4093 is a very useful chip, as it has a Schmitt-trigger and it is a nand, cmos, low power.  It can be even made to function like an amp in some configurations. It was used in debouncing circuits, oscillator circuits and input signal conditioning of digital circuits.

DMM range and AC-DC mode Logic

If you had a train of square pulses from a magnetic sensor or proximity sensor. You could use this as a monostable or singleshot to reject noise and get a clean square wave from a messy input.