[itcrowd]

I can give you some starting points, but it depends on where you are now and where you want to go. Could you answer the following so I can narrow my recommendations down?

1) What is your background? Education, experience, hobby/work.. ? Specifically, level of mathematics and physics background.

2) What do you want to do? Electrical engineering is much more than PCB design or circuit theory.

3) How much time do you want to dedicate to this learning (per week)? When do you want to "get results"? I.e. do you want to start designing PCBs next week and have them shipped to you in two weeks, or do you want the equivalent of a Bachelor's degree in EE? Or somewhere in between..?

[meridion]

1) I'm a software engineer, have a good foundation in mathematics and physics. I could use a refresher on the electrical engineering area of physics though.

2) What I want to do - for starters, small hobbyist projects like playing with sensors, displays, etc. My end goal is to be able to design cool IoT projects, such as smart security cameras, and sell them.

3) I can dedicate 1-2 hours per day. I don't expect to have the equivalent of a Bachelor's degree any time soon, but am happy with any kind of pace.

[itcrowd]

Sorry it got a bit long but here's something. Let me know if you need more or different suggestions.

I would say you need at least three things: (1) a physics textbook with some EE emphasis to get the fundamental physics (again?), (2) a circuit theory book to transform the physical knowledge to reading circuits and (3) some resource to transform the circuit theory to working PCB designs.

(1) and (2) are easy to come by (digital or in book form) and any moderately recent textbook you can pick up at a second hand store should suffice. I like physical books but YMMV. I learned using [1] and [2]. More recently, there are high-quality videos but I think it is better to get a book and then search for additional help on the topics you don't understand from the textbook explanation.

(3) is more difficult. This kind of experience can be obtained from lab exercises in a university or work experience. Unfortunately, it is very difficult to point to a single book or video resource because there are so many directions. Here are some things that may help, I tried to organize them from easy to difficult. You may need to spend a little money (<$100) in hardware in total.

Then, there is the programming side. This is most often in some C-flavor for microcontrollers so dust off your knowledge on that (or follow one of a million blogposts on Google if you're stuck).

- Get a Raspberry Pi and attach some sensors to it. There are many manufacturers of Pi-compatible stuff. Try to use the low-level functionality of RPi because it will be useful for future microcontroller projects.

- Use your Raspberry Pi with some generic sensor PCB that is not specifically RPi compatible.

- Related to above: learn about datasheets of microcontrollers. Learn that a microcontroller needs quite some external components to function (try to understand why). Learn how to program the microcontroller (extra hardware may be necessary)

- Try to mimic one of the sensor boards you got with your own PCB+microcontroller design. Maybe you can extend its functionality if you design it? Design your own PCB: integrate microcontroller, sensor, crystal, power supply+regulator, etc.

- If you want to get more fancy, you will need to spend more money, unfortunately, but in general the components are very cheap. Maybe try to get a Bluetooth chip and two Raspberry Pi's or two custom microcontroller boards to communicate? Or get a WiFi chip to communicate with your computer? Bluetooth light switch (careful with mains power!)?

- Someone else mentioned the EEV YouTube channel. Great content in general (although I can't vouch for all videos). It's nice to watch some and try to Google more information based on what interests you.

[1] "Physics for Scientists and Engineers" (now that I searched the title, I realize there are many books with the same title, from my short glances they all seem pretty equal, but I am sorry I can't remember the authors of my book)

[2] "Basic Engineering Circuit Analysis", Irwin & Nelms, see https://www.wileyplus.com/engineering-and-materials-science/... (I have a much older version)