New to electronics... Where to start? Trying to learn on my own.

Hi everybody!

This is my first post on this forum. I'm completely new to the subject of electronics and I'm interested to gain enough understanding on the subject to be able to design circuits on my own. I mean I don't want to copy simple circuits and then be happy that my LED is flashing while I have no idea how it is flashing and why it is flashing at such a rate, etc.

I use to learn staff on my own, and I think I'm good at it. But I've touched electronics several times before and each time I got confused and felt everything was vague. It seems there is some necessary information which isn't explained on online tutorials.

Well, so far I understand the ohm law and I am able to make a circuit which has some LEDs (parallel or series) and choose the right resistors to get the current I need for each LED.

For the next step, I decided to learn how to make it flash at some rate... Surprisingly after a lot of searching and reading and watching video tutorials, I still have no idea how to "calculate" and choose the right resistors, capacitors, and transistors to do it. Even more surprising, when I copy a circuit which is supposed to work in my software (Crocodile Technology 609), it doesn't flash at all. I guess the transistors in the software are different from the one used in the circuit.

I generally need good links (or even books) which step by step teach me how to "design" and NOT copy circuits.

My specific question is, how can I design a flashing LED circuit? Is there some special formula for transistors which I'm unaware of? Where can I find a good tutorial which teaches me how to do such calculations?

Is it a very complicated and difficult task? Maybe I haven't chosen a good thing for the next step.

Thanks in advance
--Koohyar

Koohyar said:

Even more surprising, when I copy a circuit which is supposed to work in my software (Crocodile Technology 609), it doesn't flash at all. I guess the transistors in the software are different from the one used in the circuit.

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No, it's not that. I've never heard of "Crocodile Technology 609", but I presume it's some kind of circuit simulator. There is a general problem with any oscillator circuit in any simulator - they normally don't automatically start oscillating, as you've noticed.

You need to cause some kind of disturbance in the circuit to get it to start, typically by injecting a short voltage pulse into it somewhere, or setting an initial condition (if your simulator allows that).

In a real circuit there's always some noise present, which is enough to start the oscillation.

Koohyar said:

I generally need good links (or even books) which step by step teach me how to "design" and NOT copy circuits.

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"The art of electronics" by Horowitz and Hill is a good book, as is "A practical introduction to electronic circuits" by Martin Hartley Jones. Those are the two on my shelf. Mine are both about 30 years old, but I expect newer editions would be at least as good.

Hello Koohyar, I really like your attitude (that you want to know how things work).

I think you need to start with basic DC network theory at such a level that you can calculate current and voltages in simple circuits with current/voltage sources and resistors, knowing the equivalent resistance of parallel and series circuits, understanding power, etc.

For your application you need to understand the time domain behavior of capacitors so that you can understand the behavior of RC and CR networks with their RC time constant. If you want to work with amplifiers also, you should know the AC behavior of capacitors also as capacitors are frequently used in filters (for example to block a DC voltage, but to pass an audio signal).

Your next step can be the behavior of the diode/rectifier, followed by the bipolar junction transistor. For your type of circuits saturation is important as that happens in many types of switching oscillators based on RC timing circuits.

Many oscillators that generate a "digital" output rely on the so-called Schmitt trigger circuit, so you should know that "circuit element" also (it is based on so-called positive DC feedback). Most electronic simulators have the Schmitt trigger as a function block (so that you don't have to built one with transistors and resistors).

Once you know the basics, behavior of RC networks, transistors and the the Schmitt Trigger, you have a basis to experiment in real world or with a simulator (provided you know how to use your simulator).

If you experiment in real world, you may need to know something about electrical safety, as you don't want to burn-down your house.

Everything you need is on the Internet, but the problem is where to find good information at your level. The books mentioned by Godfreyl are good. If your mathematics is somewhat rusty, you may try to find course lectures for radio amateurs (Full license, not Novice) and skip all RF/radio related issues. As with any general electronics book, there will be much more info then you need. If you find any problems, just use the forum.

Thanks for your kind replies. I'm glad to be a member of such a forum. Hopefully with the help of people like you I'll get to the point I want soon.

I've been reading and searching last night and noticed that the so-called "next step" I've chosen is a bit too advance for my current level. As you said I need to know some more basic staff first... and I guess I should learn to use a good simulator as well to be able to test my thoughts about the circuits and do experiments with them.

I took a look at the book you mentioned and it is very well written. I guess it has almost everything you need about transistors.

Thanks again
Let's begin the study...

Koohyar,
Yes, Your thought is right because i am also a new user such a forum. I think anyone can start replies and posting thread with your topic. But i could not understood that how to start.

Regarding the simulator, you can go for full featured free versions (such as LTspice), or go for an infinite time limited/evaluation version of an expensive package.

For your applications you can use every general purpose transistor (2N2222, 2N2907, BC547/847, BC556/856, etc) and these are present in the libraries of evaluation versions. Before starting with evaluation versions, make sure that you can save (and open again) circuits, and check the number of resistors, transistors, cources, etc you can have in a circuit. For your type of switching circuits you need the "transient simulation" option when using a simulator that is based on spice.

I hope you have the oportunity to acually build some circuits and test them in real world as in my opinion that gives even more pleasure.

Koohyar said:

good simulator

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I use the free version of SIMetrix SIMPLIS. I found it easier to learn and use than LTSpice, but maybe that's just me. They're both good.

@godfreyl: The longer learning curve for LTSpice was my motivation to mention free/limited version of other (expensive) packages also. I am using the full version of Beige Bag spice A/D V4 pro. They also have a lite (free) version. Somebody I know uses Simetrix also (with pleasure).

Thanks a lot for the great information.

Considering your advices, I think a good strategy is to start with an easy to use simulator. Because the circuits I'm going to test are simple, such a simulator meets my needs. Meanwhile, I also begin learning a full featured simulator, so when my circuits get more complicated, I will have already learned the suitable simulator as well.

Thanks again

Why not learning one simulator at the time? Many electronics simulators are spice based and the large difference is in the user interface. It would be nice if you can use a simulator that somebody around you already knows. It will save you time (so that you can use your time to study electronics instead of struggling with the simulator).

It would be nice if you can use a simulator that somebody around you already knows.

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Good idea.

I think I need to refresh my math/physics knowledge as well...
The whole process indeed isn't a short, easy task to do. But this time I'm not going to give up!!!

You will definitely arrive in situations where you don't know how to continue, some hurdles will be high. With the help of others (including this forum) and the will to learn, you will make it. Make sure that you get several books and/or study material. Sometimes reading (some parts of) another book helps to take a hurdle.

In my opinion it is good to have both theoretical and practical oriented books.

The warm welcome I have received here indeed gives me extra energy and encouragement to continue. When you know there is always a place to ask your questions, you don't fear the probable hurdles which may appear in the way. Hopefully when I gain enough knowledge I'll be able to help other members of the forum too.