Reset Protection For Computers

Description: This protection circuit is placed between the reset switch and the motherboard. The earth connection of the computer must be linked to the terminal of the protection circuit. The protection circuit can draw its power from the computer supply. When the circuit is installed, activating the reset switch will not immediately restart the computer. Instead, a buzzer will sound to alert the user of the reset operation. The buzzer is activated for 4 seconds by monostable IC1A, which is triggered by the reset switch. During these 4 seconds, the output pin 5 of IC1A ensures that the reset function (pin 10) of IC1B is disabled. When the reset switch is pressed again, monostable IC1B will be triggered, initiating the reset procedure. Transistor T2 is then activated for 0.5 seconds, and the buzzer is deactivated via resistor R11 and diode D4. The circuit configuration around T1 and N4 ensures that IC1A can accept trigger pulses again 10 seconds after the monostable time of IC1B has elapsed. This design prevents unauthorized operation of the reset switch, such as by children.

This protection circuit serves as a safeguard for the motherboard’s reset functionality, effectively preventing accidental resets that could disrupt system operation. The circuit is powered by the computer's supply, ensuring it remains functional without requiring additional power sources.

The operation begins when the reset switch is pressed. IC1A, a monostable multivibrator, generates a pulse that triggers the buzzer for a duration of 4 seconds. During this time, output pin 5 of IC1A disables the reset function of IC1B, preventing an immediate restart of the computer. This delay is crucial as it not only alerts the user with an audible signal but also prevents unintended resets.

Upon a second press of the reset switch, IC1B is triggered, initiating the reset process. The activation of transistor T2 for 0.5 seconds allows the buzzer to turn off, indicating the end of the alert period. The use of resistor R11 and diode D4 in this stage ensures that the buzzer is efficiently deactivated without affecting the overall circuit functionality.

Furthermore, the design includes a delay mechanism that allows IC1A to accept new trigger pulses only after 10 seconds following the completion of IC1B's monostable time. This feature is particularly beneficial in environments where accidental resets by children or unauthorized personnel may occur, providing an additional layer of protection for the system.

In summary, this protection circuit enhances the reliability and usability of the reset function in a computer system, combining alert mechanisms with safeguards to prevent unintended operations. Its thoughtful design ensures that the user is adequately informed while maintaining control over the reset process. This protection circuit is inserted between the reset switch and the motherboard. The earth connection of th e computer must be linked to terminal of the protection circuit. The protection circuit can draw its power from the computer supply. When the circuit has been fitted, operation of the reset switch will not immediately restart the computer. Instead, a buzzer will sound to alert you to the reset operation. The buzzer is actuated for 4 s by monostable IC1A, which is triggered by the reset switch. During these 4 s, the output, pin 5, of IC1A ensures that the reset function, pin 10, of IC1B is disabled.

When the reset switch is operated again, monostable IC IB will be triggered and this starts the reset procedure. Transistor T2 is then switched on for 0.5 s and the buzzer is deactuated via Rll and D4. The circuit around T1 and N4 ensures that IC1A can accept trigger pulses again 10 s after the mono time of IC1B has lapsed.

This arrangement prevents, for example, children operating the reset switch.