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.
1Hz signal generator circuit
230V, 50Hz, single phase AC mains is stepped down by centre tapped transformer X1 to deliver a secondary output of 9V-0-9V at 100 mA. The transformer output is rectified by a full-wave rectifier comprising diodes D1 and D2 and filtered by capacitor C1. This provides required DC voltages for operation of the electronic circuit.
![1Hz Signal Generator Circuit](http://electronicsforu.com/wp-contents/uploads/2016/04/6BB_1.jpg)
The 50Hz input signal is also taken from the secondary winding of transformer X1 and fed to clock pin 14 of decade counter 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).
Construction & testing
After construction and testing, enclose the circuit in a suitable cabinet. This circuit can be easily assembled on a veroboard.
The article was first published in April 2007 and has recently been updated.