Learn simple AND and OR logic gate without IC

Can we use AND and OR logic gate with Diodes? Yes, we can. The past, we have used only a digital logic circuit by IC.

But, in truth. We do not need any ICs.

Use Switches or Diodes or transistors connected as a logic circuit.

See in the circuit below. We use switches and diodes connected as AND and OR gate. To make us understand the meaning of a logic circuit in one sense.

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How it works

AND and OR gates without IC

Let’s learn both simple logic gate.

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(A) AND gate by switch Connect switches in series. We will get a logic of the AND gate. When a closed switch is like a high input signal “1”. And, if the opened switch means “0” status.

Use switches as an AND gate

If we turn on all switches. They are a “1” status. So the voltage goes out of the output. It shows “1” states. We will see that the output is a high status because all inputs are high logic only.

(B) OR gate by the switch—Connect switches together in parallel. We will see that if either switch is closed. Or input is “1”. It will make output into “1” immediately.

Use switch as an OR gate

(C) AND gate use Diodes Both images above are basic gate using the switch. We may not use it in real uses. Also, we can use diodes and resistor into AND and OR gate on the sequence.

See in the image below. Now the input and output signal are voltage level same the digital ICs.

If we enter a high voltage (“1”) to the input terminal of both the diodes. It will cause non-current flow through the resistor. Then, the output will be high voltage.

But If the input is low voltage. There will be the current flow from power supply through the resistors and diode to that input. It makes output is also as low voltage.

Use Diodes as AND gate

(D) OR gate using Diodes Some I use this diodes circuit because it is easy and cheap. We use the diodes and resistors to connects as OR gate.

Use Diodes as OR gate

If either input is high voltage. It causes the current can flow through the diode to the resistors. So, the voltage is across them as of “1”.


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