1Hz Clock Generator Circuit Using COB

Let's familiarize with a COB - chip on board device by building a precision 1Hz clock generator. Circuits that usually generate 1Hz clock makes use of ICs with variable capacitors but they are not very precise. ( micro controller based one should be precise but it costs large ). better accuracy can be obtained by a COB found inside a digital clock, which is cheaply available in the market.

1Hz clock generator circuit diagram : Click on the image to enlarge

The COB is a small pcb consist of an IC chip capacitors and quartz crystal, etc. Here's the some important points to note before you assemble the clock generator.

• R1, C3, diodes D1 and D2 shown in the circuit convert 5V DC into 1.4V DC which is the supply voltage to the COB.
• A ½Hz clock is available at terminals A and B with a phase difference of 90o, these pins are coupled using  capacitors C1 and C2 to obtain a complete 1Hz clock.
• Op-amp IC CA3140 used to amplify the output of the COB to a considerable level.
• R4 and R3 is used to set the gain of the op-amp. 
• T1 and T2 transistors further amplifies the clock output to drive the digital clocks and timers.
• Preset VR1 is offset null control used to adjust proper 1Hz pulse at the  output terminal ‘E’.
• LED blinks every one second interval.

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