Practical Electronics & Circuits 101 – Switches & Relays

The 11th video in the series Practical Electronics & Circuits 101, where I explain the basics of the theory behind circuits with a focus on using this knowledge for actual projects. This episode focuses on switches and relays.
Subscribe and stay tuned for more lessons and projects.

Relay module boards on Amazon:

These are affiliate links where I earn a small commission for purchases at no extra cost to you.
This is the easiest way to help the channel, thank you!

Donations

Chapters:
00:00 Intro
01:05 Simple SPST & SPDT switches
04:24 DPDT switches and adding more poles
06:26 Switch power ratings
07:16 Overview of relays
08:58 Relays vs transistors when used as a switch
12:51 Coil voltage & how to use a relay
16:47 Simple example controlling a relay with a Raspberry Pi
24:07 Outro

[PhazerTech]

A few corrections. The 2N7000 worked for this application but it's not a great choice because 150mA is pushing it. After looking at the datasheet again I'd use a different transistor for peace of mind in long term use. For example the 2N2222 is a BJT that is suitable here. The IRF3205 MOSFET I showed in the previous video is another good choice but it's large and overkill for this. It seems the most appropriate MOSFETs for this are mostly surface mount, not breadboard/stripboard compatible. But if you go with the relay module boards that I linked in the video description then you won't need to worry about this.

Also like I mentioned, MOSFETs don't require a resistor in between the gate and the RPi output pin, but in some cases you might want to include one to protect the Pi in case there's a short across the transistor. This resistor should be relatively small, only about 100 to a few hundred ohms. If you go too high then the transistor might not be able to fully turn on.

And finally, I forgot to mention the jumper on the relay board allows you to reverse the input signal, in other words the relay will turn on when it receives a low signal from the Pi, not a high signal. But in most cases you can ignore the jumper.