Logic gates are the building blocks of computers, and transistors have made logic gates cheap, light weight, and reliable.The transistors' three metal legs -- the collector, base, and emitter -- control the flow of electrons and determine whether the charge is high or low, and these zeros and ones make our digital words, pictures  and sounds.

I'll show you the first logic gate I built. I made it at TechShop.

Microprocessors have millions of gates, but some spare change yields a handful of electronics parts, enough to make a logic gate and to see the beauty of computing one bit at a time.

With two transistors you can create your first logic gate, an AND gate. An AND gate responds when both inputs are high or true. If you’re looking for your black cat, Damian, the thing you want must be both a) black and b) a cat.

Is it black?       Is it a cat?      Could it be Damian?
No                     No                    No
No                     Yes                   No
Yes                    No                    No
Yes                    Yes                   Yes

Now let’s go electric!

Step 1: Parts

Two NPN 2222 transistors

Two push button switches (I got mine from a spare parts box at Tech Shop).

Three resistors (two 1 kilo ohm and one 100 ohm)

A battery and connector

4 bits of wire
<p>I am not very good at electronics. Could you please tell me the use of the resistors in this AND gate? Any response will be greatly appreciated.</p>
It's been a while. The 330 resistor is to reduce the current for a regular LED. Otherwise it would pop. I'm guessing I used the other resistors to protect the transistors.
<p>Thank you!</p>
Now I remember. If only one of the gates is closed, the resistance is sufficient to dim the light nearly entirely. Thanks for checking.
Very great and neat project, will any NPN transistor work ?
<p>A 2n3094 should work too.</p>

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