This is the 1Hz clock generator circuit with Chip On Board (COB). Commonly, the circuits to produce 1Hz clock for digital clock and counter circuits applications implement ICs in conjunction with a crystal and trimmer capacitors, etc. Even so, equivalent or improved accuracy could be obtained working with a chip-on-board (COB) device found inside a digital clock, that is readily offered in the marketplace. This COB includes IC, capacitors and quartz crystal, etc that are installed on its surface. It operates on 1.4 volt DC supply. This COB could be utilized to get 1Hz clock.
Resistor R1, capacitor C3, diodes D1 and D2 shown in the circuit change 5V DC into 1.4V DC. A ?Hz clock is accessible at terminals A and B with a phase variation of 90o. The two outputs, are put together making use of capacitors C1 and C2 to acquire a complete 1Hz clock. This 1Hz clock pulse features a extremely low amplitude of the order of a few milli-volts which can’t be utilized to drive the digital circuits instantly. This low-level voltage is amplified several times by operational amplifier (op-amp) IC CA3140.
The op-amp CA3140 is connected in a non-inverting mode, and its gain is set by resistors R4 and R3. Capacitor C2 minimizes the AC gain and undesired stray pick-up and thus increases stability of the circuit.
The input impedance of IC CA3140 is extremely high and thus there is absolutely no drop at the input when 1Hz clock signal of low level is connected across its input terminals from the COB. Amplified 1Hz clock pulse is accessible at its output pin 6, that is further amplified by transistors T1 and T2 to drive the digital clocks and timers.
Preset VR1 is offset null control utilized to adjust accurate 1Hz pulse at the output terminal “E”. Connect one LED in series with 220-ohm resistor between the terminal “E” and ground and alter preset VR1 till the LED blinks once every second. When utilizing the COB, affix the same on a general-purpose PCB working with rubber based adhesive and solder the terminals neatly making use of thin single-strand wire.
Note: The COBs utilized in different watches may differ somewhat in their settings. But by trial-and error one can always find out the proper points corresponding to points A, B, C and D.
Download 1Hz clock generator with Chip On Board (COB) circuit in PDF document (include the configuration of COB):