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Build Precise Time Delays with a 12-Stage Binary Counter
Description
Extended delays of several hours can be achieved through the utilization of a low-frequency oscillator and a binary counter, as illustrated below. A single Schmitt Trigger inverter stage (1/6 of 74HC14) functions as a squarewave oscillator, generating a low frequency of approximately 0.5 Hertz. The 10K resistor connected in series with the input (pin 1) minimizes the capacitor discharge current through the inverter's internal protection diodes should the circuit be abruptly disconnected from the power source. This resistor is recommended for implementation.
The counter's frequency is divided by two at each subsequent stage of the 12-stage binary counter (CD4040), resulting in approximately 1 hour of time before the final stage (Q12) transitions to a high state. Alterations to this duration can be realized by modifying the oscillator's frequency or employing different RC values. Each successive stage changes its state when the preceding stage moves to a low state (0 volts), consequently, the frequency at each stage is one-half the frequency of the stage preceding it. Waveform graphics are provided for the final three stages. To initiate the delay cycle, the counter can be reset to zero by momentarily connecting the reset line (pin 11) to the positive supply.
Schmitt Trigger Inverter (74HC14)
The 74HC14 is a versatile digital Schmitt Trigger IC. It's a monolithic integrated circuit designed for switching and oscillation applications. This particular stage, utilizing one-sixth of the 74HC14, acts as a square wave oscillator. The Schmitt Trigger input provides hysteresis, ensuring that the output switches reliably even with slight variations in the input signal. This feature is beneficial for generating stable and predictable square waves, essential for accurate timing circuits. It is available in the DIP-14 package and is a common component for various electronic projects, particularly those requiring reliable waveform generation and switching. It's rated for operation from -4.5V to +16V DC.
Circuit diagram
