Step 9: Transistors

A transistor takes in a small electrical current at its base pin and amplifies it such that a much larger current can pass between its collector and emitter pins. The amount of current that passes between these two pins is proportional to the voltage being applied at the base pin.

There are two basic types of transistors, which are NPN and PNP. These transistors have opposite polarity between collector and emitter. For a very comprehensive intro to transistors check out this page.

NPN transistors allow electricity to pass from the collector pin to the emitter pin. They are represented in a schematic with a line for a base, a diagonal line connecting to the base, and a diagonal arrow pointing away from the base.

PNP transistors allow electricity to pass from the emitter pin to the collector pin. They are represented in a schematic with a line for a base, a diagonal line connecting to the base, and a diagonal arrow pointing towards the base.

Transistors have their part number printed on them and you can look up their datasheets online to learn about their pin layouts and their specific properties. Be sure to take note of the transistor's voltage and current rating as well.


<p>This was really helpful! I think I need to dive into a project to really grasp it though...</p><p><a href="http://amzn.to/2eefKw6" rel="nofollow">Would this be a good kit to help learn basic electronics?</a></p>
<p>so far helpful but a little cunfusing, i think ill get it</p>
<p>Is there a place where you would recommend getting a job lot of equpiment on the reasonably cheap?</p>
<p>What sort?</p>
<p>When you say ike, make this ciruit, but i dont have that many components to do any of it with. Where do you rekon that i can get a job lot from.(Young student so dont have much funds)</p>
<p>What <strong>types</strong> of components?</p>
<p>Thank you :)</p>
<p>For any soon-to-be electronic enthusiasts, &quot;Arduino&quot; is something for you to look into.</p>
<p>Nice kit, but I would recommend the new <a href="http://www.amazon.com/dp/B01EKO6FZU" rel="nofollow">Make: Electronics Component Kit 2nd Edition</a> for a beginner in the field as it will teach them all of the circuits and electronic theories they need to know before getting into Arduinos. This kit has all the components for the beginning of the new Make: Electronics 2nd ed book which is the best book for newcomers looking to learn electronics and build circuits.</p>
<p>Thank you so much! I will buy that one first. If something is explained from scratch, I can grasp it, but with missing steps I get confused and discouraged. That's why I am liking this website too. If I had gotten arduinos first, I would have probably gotten confused. I am planning to get arduinos, but after I get the kit you recommended. </p>
<p>No problem at all! I am happy to be helpful where I can, and that book and component kit make learning electronics easy and fun! Enjoy.</p>
<p><strong>Why to reduce flow of current in circuit??</strong></p>
<p>When current flows through the circuit it carries some amount of heat that depends on its strength (i.e. amps.) Large current carries large amount of heat. Every component in the circuit carries designated limit of current that it can pass through, so that it should not burn due to excess heat causes due to current. Therefore, it is important to limit the current flowing in the circuit.</p>
<p><strong>The rate of reversal is measured in Hertz, which is the number of reversals per second. So, when they say that the US power supply is 60 Hz, what they mean is that it is reversing 120 times per second</strong></p><p><strong>How can calculate the number of reversing per second based on frequency, could you please explain it?? </strong></p>
I made the circuit but it's not giving me a high and low sound just a straight toned ring. What am I doing wrong?
<p>Nothing. You have done it right. It is the relationships between high 5V and low 0V that creates the ringing tone. The high and low voltages are not related to sound, but the shape of the electrical wave being created (on, off, on, off, etc ---__---__---__--- )<br><br> A tone is then created at the frequency of the square wave (the speed at which the signal is being turned on and off). You can increase and decrease the frequency of the tone, but you will still only have a single tone because you have only created one uniform square wave. </p>
<p>what do you mean by 'Ground'?</p>
<p>Ground is another name for the - (the opposite side of the +)</p>
I'm starting out in electronics and on a schematic when a wire seems to split off two ways on a right angle that just means it is connected to both of those components correct?
<p>Hi !</p><p>I am vinay and I want to enlighten a 12 LED by the battery of my bajaj caliber 115 motorcycle, I want to know how can I use CD 7812 voltage regulator to get a constant 12 V DC while the bike is running ( when it will produce around 14.5 V).</p>
when you say ground do you mean negative<br>
Expertman, In early Electronics, ask about anything that you feel uncertain about. Its a &quot;grey&quot; area, an important question. In response, &quot;Ground&quot; and &quot;Negative&quot; are used with the same intent.They refer to the &quot;polarity&quot; of the power supply(Battery in this case) and where the 'pin' of a component's intended destination is(These components are usually labeled with this, if necessary) if unsure, find it online-(Not in a 'Blog', use 'DIGIKEY') Great prices, too!<br>. Good luck, hope this helped!
<p>i guess in both images,, wires are connected in parallel...</p>
i've been looking for this all over the endless fields of the internet. so, just tanks a lot
<p>apt site for beginners</p>
<p>This was very educational and informative for me thanks</p>
<p><strong>nice site for beginners as well as professionals</strong>.</p>
<p>Michael U.</p><p>Thanks alot for this tutorial, it is so rich</p>
<p>Hi,<br><br>Thank you so much for this tutorial.<br><br>FYI , on step12 (ie LED) you mentioned that the flat notch indicator is on anode end , but its on cathode end of the LED. Please check it.<br><br>Thanks.</p>

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Bio: My name is Randy and I founded the Instructables Design Studio. I'm also the author of the books 'Simple Bots,' and '62 Projects to ... More »
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