Thought process behind a project

[combustin007]

Hello Everyone,

I am new to the forum but have been fascinated with circuits for all my life. I have been a programmer for the past 10 plus years and and have always wondered how different is a thought process when it comes to circuits.

Lets say I came up with an idea for a very simple thermostat which only displays the outside temp. How does one decide what parts be needed it. I understand now with industry advancements, I can employ a micro-controller and program it, and it should be ready to performed the programmed task and follow the logic.

How does one know that with that micro-controlled, I will need a this many resistors, and then this many other parts.

Any wisdom will highly be appreciated.

Thank you.

 

[Noggin]

Well, the first thing to decide is it is going to be microcontroller based or based on a more simple IC? Assuming you decide that it is going to be microcontroller based, you have to determine how you are going to measure the temperature. There are many ways to do it. A simple way is to use a thermistor (basically a resistor that changes depending on temperature). So now you have an MCU and a thermistor. So now you need a constant current source to go through the thermistor so you can read the voltage across the thermistor in order to calculate its resistance. So now you have to build a constant current source such as one based on an LM317. In order to do that you need a couple more resistors. Now, you need a display, and you need power supplies, ESD protection, etc etc

Its basically an iterative process.
1. Identify a needed part
2. Look at datasheet to determine what it requires to operate
3. Determine from datasheet or experience what is necessary to tie it in to other compoents
4. Go to step 1

 

[combustin007]

Thank you Noggin for your wisdom. So lets say if I would like to build a simple circuit where should I start? I have very minimal knowledge of the electronics components, but it is a learning process and I know that it will take me time to get acclimated with the lingo as well.

I have read couple of books regarding basic electricity, and I would like to build prototype for learning purpose. Where should I begin? I have been checking online tutorials out but until I roll my sleeves up and dive in, the learning process will be very minimal.

I would like to learn how to design the circuits first. Can you suggest a good design package?

Appreciate your help.

Thanks

 

[crutschow]

Initially you need to go from the general to the specific and determine exactly what you want the circuit to do, realizing that the more you want, the more complicated the circuit will likely be. You many decide as you get into the design that you can really get by with fewer features to simplify the design.

These days µCs are so inexpensive that most designs use one for all the logic and display functions, and use ICs to perform the analog (and possibly some digital) interface to the µC's inputs and outputs. Of course there are dozens of different types of µCs with different bit capacities, functions, I/O lines, etc., so selecting the one that is appropriate for your task is a job in inself.

A good starting place to determime which analog components to use is by going to the various IC manufacturer's websites and search for ICs that may do what you want (such as temperature sensors in your example). (And of course a Google search will always turn up a bunch of info). There would be many different types so you would then need to decide which appears the best for your requirements, based upon part cost, package type, output format, accuracy, temperature range, etc. Along with data sheets, manufacturers often have application notes which are also very useful in helping you understand how to use a particular device.

It's an iterative process (which is often time consuming) as Noggin stated. And there's really no substitute for experience, so contacting forums such as this with your specific questions will usually elicit a helpful answer as you move along in the design process.

 

[crutschow]

I would like to learn how to design the circuits first. Can you suggest a good design package?

One good way to learn about analog circuit operation is to use a SPICE based circuit simulator program. A good free one to start with is LTSpice from Linear Technology. These programs allow you to see how a circuit operates (or doesn't) without having to build it. There are web forums on LTSpice and SPICE simulation that can help you get familiar with it.

Read some tutorials on op amp and transistor circuits. Start simulating some simple op amp or transistor circuits and go from there. That will give you insight that no amount of reading can.

I do circuit design and simulate all my circuits before building them. I find a lot of bugs that way which gives a high probability that the circuit will work properly after it's built.

 

[combustin007]

Hello Crutschow,

Thank you so much for your thoughts. I will get started.

 

[MrAl]

Hi there,

I have to second that nomination to use a circuit simulator, because you
can do many types of circuits with that and dont have to worry about
burning out parts or whatever.

Think back when you first learned programming. You probably didnt even
know what a 'goto' was right? Then you learned it, maybe used it, then
found out the pitfalls of using it, although you may still incorporate it
now and then. Well, this is like electronics too, you first learn this and
then that and then more about this and that and finally at some point
your accumulated knowledge allows you to do various tasks, and the
more you do this stuff the more you know and the more you know the
faster you learn and the more you learn the more you can figure out
how to design your own circuits.
Also, you might think about how many programs you have viewed (and
possibly debugged) over your life so far, and how viewing them helped
you learn more about programming. Think about how it would be if you
never saw a program before, and then think about how many programs
you viewed again and how many you have programmed yourself.
Well, electronic circuits is similar in this respect, because the more
circuits you look at (analyze) the more you learn and the more you
understand what is going on.

Also, math is a big player in really understanding circuits. Learning
how to analyze a circuit helps to understand, and this requires math.
Calculus is a must, but even algebra and trig can get you pretty far.

As far as components, you would start with resistors, move to caps,
then to inductors, then diodes, then transistors, etc., so a good
place to start is learning all about resistor circuits and Ohms Law.


Another analogy to programming might be this:
A large circuit is sometimes like a large program, where the sub circuits
are like static instances of a class object. Often a bunch of smaller circuits
make up a big circuit, where you already know what the smaller circuits
do so that makes it easier to understand the whole larger circuit.

 

[Diver300]

Get something like a PICKIT2 debug express Product Search - microchipDIRECT
That will let you light LEDs, read in from switches or analogue signals and gives you some room to wire up other stuff.

It's all powered from a USB port so it lets you get program running at little cost.