Hit the simulate button and you should notice the reading of a tiny voltage, on the order of a few millivolts. The first circuit is the one we want to look at here. Each is the circuit for a different logic gate, and each multimeter measures the voltage across the output. You should see three breadboards with a multimeter each. Now take a look at the 123D circuit ( click here). Using transistors as switches, the circuit can be controlled completely electronically. In essence this is like wiring two switches up in series current does not flow to the output unless both switches are closed. Yes I realize my artistic skills never left the second grade. In the circuit diagram above you can see a simple AND gate built using two transistors. Most logic gates can be made quite easily with transistors. This particular truth table is for the AND operation notice that the output is 1 only when both inputs are 1, as you would expect. This kind of table lists all possible combinations of inputs, and shows you what their corresponding outputs would be. The table below the diagram is called a truth table. The AND operation is often called Boolean multiplication because the result is as if you 'multiplied' the two inputs, and is also written as F = AB, similar to multiplication.

The terminals marked A and B are the inputs, and the one marked F is the output.Īn AND gate determines its output by the following rule: if both inputs are 1, the output is 1 if either or both inputs are 0, the output is 0 (recall that 0 and 1 are 'low' and 'high' voltages, respectfully). The circuit symbol for a two-input AND gate is that funny bullet-shaped thing. The first type of gate we will look at is the AND gate. You will need to fork the circuit to be able to experiment with the circuitry like we will a little later, but if you can't be bothered its OK if you just hit the simulate button and get started. There is a 123Dcircuits circuit that goes with this Instructable here. Logic gates may be strung together and combined almost infinitely, and such combinations can be designed to make pretty complex decisions based on any number of variables.īy the end of this Instructable, we will have covered: The logic gate also has one output terminal, and the voltage at this terminal will be high or low depending on the type of gate and the inputs received. These inputs can come from anything, be it a battery, a sensor, some IC or even another logic gate. Typically a high voltage is read as a 1 and a low voltage as a 0.

So what are logic gates? Logic gates have one or more input terminals, and the voltage at these terminals are translated into Boolean inputs of 1 or 0. In this Instructable we will talk about a few of the simplest of these devices, and see some of the fun things you can do with them. Logic gates are some of the basic building blocks of digital logic circuitry.

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