Resistors - A simple circuit

The first analysis we will do is as promised, simple. But we can demonstrate and reinforce a few extremely important fundamental principals here. Remember, the idea behind this website is for students to learn the practical aspects of electronic theory. We all remember from school the rules related to series and parallel resistors. Using ohms law we can calculate the following:

The current flow through R3 never changes and will always be 10ma. This is simply I=E/R or I = 10/1000 or .01 which equals 10ma.
The voltage drop across R3 = 10V always, regardless of the positions of SW1 and SW2.

SW1 Open and SW2 Open:
Total current flow = 10ma
Voltage Drop across R1 = 0V
Voltage Drop across R2 = 0V
Voltage measured from Ground to the point where R1 and SW1 are connected together = 10V Voltage measured from Ground to the point where R2 and SW2 are connected together = 0V Current Flow through R1,R2 and R4 = 0ma


SW1 Closed and SW2 Open
Total current flow = 15ma
Voltage Drop across R1 = 5V
Voltage Drop across R2 = 0V
Voltage Drop across R4 = 5V
Voltage measured from Ground to the point where R1 and SW1 are connected together =5V
Voltage measured from Ground to the point where R2 and SW2 are connected together = 5V Current Flow through R1 and R4 = 5ma
Current Flow through R2 = 0ma

SW1 Open and SW2 Closed
Total current flow = 15ma
Voltage Drop across R1 = 0V
Voltage Drop across R2 = 5V
Voltage Drop across R4 = 5V
Voltage measured from Ground to the point where R1 and SW1 are connected together =10V
Voltage measured from Ground to the point where R2 and SW2 are connected together = 10V
Current Flow through R1 = 0ma
Current Flow through R2 and R4 = 5 ma

SW1 Closed and SW2 Closed
Total current flow = 16.77ma
Voltage Drop across R1 = 3.3V
Voltage Drop across R2 = 3.3V
Voltage Drop across R4 = 6.7V
Voltage measured from Ground to the point where R1 and SW1 are connected together =6.7V
Voltage measured from Ground to the point where R2 and SW2 are connected together = 6.7V
Current Flow through R1,R2 and R4 = 16.7 ma

The principals shown here are very basic. I have found many times though in working with technicians, a tendency to over complicate circuits like this. For example, you may want to factor some change in current through R3 when you throw the switches when in fact nothing changes. The reason is that R3, is connected to VCC and Ground, a power supply that in all properly designed electronic circuits have more than enough capacity to supply power to all circuits.

In summary, I hope I have not made any errors in this submission. Secondly, I hope that if anyone reading this finds any error or has a question, they will submit for discussion.

Mission Statement

The purpose of this Blog, is to increase the understanding of basic electronic theory for the benefit of others and myself.
I will post circuit board schematics either in total or partialy. I will then focus on each aspect of the functional block diagram and attempt to analyze each section. I will seek the input and comments of others as we walk our way through the circuit. The rule of thumb here will be the KISS (Keep It Simple Stupid) principal. If we want to understand electronic fundamentals, we do not need to start by trying to understand how a super computer works. As we work through these circuits, in following my KISS principal, I will try stick as much as possible to the basics (which might be the limit of my own understanding), but will invite our community of engineers and subject matter experts to delve into a more thorough explanation for those that may want to further explore a subject.
My name is John Somerville, and I am the president of a telecommunications circuit board repair depot. I have been involved in various aspects of electronic circuit repair and design for more than 25 years and am not a degreed electronic engineer.
Over the years I have worked with literally hundreds of technicians and engineers with a wide range of experience levels and educational backgrounds. It has been my experience as it relates to fundamental electronics that these people can be broken down into two groups, those that get it and those that don't. It seems to me that there is almost no limit to the complexity of the circuits that can eventually be understood by people that understand the fundamentals. The goal of this Blog, is to move people into the group that "gets it".