Digital Security System

Essay by PaperNerd ContributorHigh School, 12th grade April 2001

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Introduction This year's electronics systems project was a computer security system. It was a complicated project, because we first had to research the different ways for the project to be done. Internet was the main way of research for this, and for the most part it didn't turn up anything as far as what we could use. So, in turn we sat down and started to think, what would happen if we used a digital security code. So that's what we did, we put together a complicated system incorporating a dual quad-input NAND gate, a quad dual-input OR gate, and an inverter. When the correct combination is entered it triggers a SCR that in turn triggers a relay, making the power turn on in the computer. If the wrong combination is entered it triggers another SCR that triggers a relay controlled alarm circuit giving power to a piezo buzzer emitting an alarm sound.

Technical The circuit supplies it's own power so it doesn't interfere with the power supply's wattage ratings. The power is a power supply circuit that incorporates the 7805 regulator chip. In the circuit all of the chips must have a constant 5 volt supply. All of the switches on the circuit are DPST, with one of the throws on the negative 5 volts, another throw having a positive 5 volts, and the pole having to be selected to either +5 or "“5 volts. When the pole is selected to the "“5 volts it sends a signal of 0, but if you select +5 volts it sends a signal of 1. When all of the inputs to the NAND gate are 1's it will emit a signal of 0 when that signal hits the inverter it turns it to a signal of one. When this signal is...