Count Down Timer with PIC16F84A

Posted on Jan 10, 2013

The choice of material to read or drive is the definition of three digits (Bit), RA0, 1,2 PORTA of the PIC at the entrance of 74HC138A. To select a material for reading or driving an output of 78HC138 is '0 '(Low), forcing the transistor (2SA1015) to conduct and thus is the material with the feet of PORTB. This function ensures that there will never be found simultaneously connected to PORTB two materials, since the remaining transistors are off. Switches BCD (inputs), the start button (input) and LED Display (outputs) are controlled solely by the pins RB0 - RB7 of PORTB. Depending on what material is selected and modified the state of PORTB (If it is input or output).

Click here to download the full size of the above Circuit.

Prevention of short circuit through the breakers PORTB BCD Because through the contacts of BCD switches may be shorted pins of PORTB when it acts as output (driving), have been placed in preventive circuit pathways to prevent flow of current. Pull up Operation Since the BCD switches on this circuit give reasonable '0 'in closed contacts, to identify the microprocessor has the entrance to each leg to be used consistently logical '1'. Internal Pull-up operation is applied only when the situation in the PORTB pins made from output, input, and if you specify zero '0 'in place of the registrar RPBI OPTION. If the PORTB output serves as the pull-up function does not. At the stop button of the timer is connected to PORTA added external resistor Pull-up, because this function is only supported on the feet of PORTB. Relay Output At the foot of RA3 PORTA is connected to a relay coil, a switched contact, where you can drive any secondary low power device. Each leg of the PIC can provide power in the range of 25-mA. If the relay used in the circuit for the power consumed by the coil is 23-mA, which is very close to the limit. Therefore to avoid possible destruction of the PIC to drive the relay is not directly but through a transistor can provide current in the range of 150-mA. Timing Circuit For the timing of the processor used a ceramic filter (Resonator) or 10MHz crystal and two 22pF...

Visit page

Leave Comment

characters left:

New Circuits

Zero consumption Anti-theft High power Code Switch for E-Bike Batteries

This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
Ultrasonic distance finder circuit

The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Simple Metal detector circuit with CD4030

Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Fully automatic watering circuit for flower pots

Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
Simple deep searching metal detector circuit

The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
Sub-Harmonic Bass Converter for Electric Guitars

The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
Echo Depth Sounding Sonar for Boats

In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
100W HiFi Audio Amplifier Circuit

This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
Plant-Pot Water Level Indicator Circuit

A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....

Create NOW your QR MENU for your Restaurant / Hotel / Bar / Caffe,

Comprehensive ordering/paying features. fully personalized to suit your Business.

Update Anytime! Easy and Simple!

Popular Circuits

Coil-less FM Transmitter

The RF oscillator using the inverter N2 and 10.7Mhz ceramic filter is driving the parallel...

Energy Consumption Monitor Circuit

The ECM circuit consists of four sections, as shown in the block diagram. A power converter...

musical continuity

A continuity tester is handy for checking that there is an electrical conducting path between two...

1w btl audio amplifier

The TDA8581(T) from Philips Semiconductors is a 1-watt Bridge Tied Load (BTL) audio power...

Dual level liquid sensor circuit design using CA3410 op amp

This level liquid sensor electronic circuit diagram is based on a common Ca3410 operational...