Accurate 1Hz Generator

Accurate 1Hz squarewave pulses are required in stopwatches and other digital circuits. Here is a low-cost, general-purpose 1Hz signal generator without using a crystal oscillator.

Step 1: Components Required

Diode

• 1N4007--------2

Resistor

• 10KΩ
• 470Ω

Capacitor

• 1000μF, 35V

IC

• CD4017------2

LED

• RED

TRANSFORMER

• 9V-0-9V, 500mA

PCB

• General Purpose PCB

Connectors

• 2 pin screw terminal -------- 3

Step 2: Schematic Diagram

Explanation of Circuit

Diode

The two diodes D1 and D2 are used to form full wave rectifier.The output of full wave rectifier is pulsating dc.

Capacitor

The capacitor C1 reject the ac signal and allows only DC signal, because the capacitor C1 is connected in parallel.

Capacitor allows AC signal if it is connected in series and blocks DC.Capacitor allows DC and blocks AC if it is connected in parallel.We have connected the capacitor in parallel because the circuit needs to be powered with DC Voltage.

IC CD4017

IC1 which is wired as a divide-by-5 counter via resistor R1. IC1 now produces 10Hz output at its pin 12, which is further given to the clock pin of another IC CD4017 (IC2), wired as a divide-by-10 decade counter. The output of IC2 can be seen as a 1Hz clock pulse on the screen of the oscilloscope and also as one flash per second on LED1 connected in series with the output load (resistor R2).

LED

It is used to indicate the 1Hz Signal by flashing of LED.

Step 3: Assembling the Schematic

I had assembled the circuit in a general purpose PCB according to the schematic diagram.

Step 4: Application

• It is used to create blinking effect of LED.
• It is used in many digital circuits like counter,timer,stopwatch,etc.

Step 5: Video

Comments

[rafununu]

This won't work in US where mains frequency is 60Hz. Take care cos all 4017 don't react the same, some of them need a noticable transistion on the clock input (TI I think), I've got this issue to solve in 1983 !

[tytower]

You should explain that the incoming a/c is at 50 hz divided by 5 gives
10hz divided by 10 gives 1 cycle per second. the pulse is taken from
one side only! Thats assuming the powerco keeps it at exactly 50 hz which it rarely does.