# Basic electronics explained

Well, recently we launched an online course on robotics as a part of CFI online course series.
I felt motivated to share my knowledge even here. So, all the course modules which I create myself, I will add them as blog posts too! Hope, they will be interesting for everyone.

-> The Apollo computers had less processing power than a cellphone!!
-> “Moore’s law” is the observation that, over the history of computing hardware, the number of transistors in a dense integrated circuit doubles approximately every two years.

Now the serious part
The world of DC electronics is usually divided into 2 parts:

• Digital circuits- In this domain, we consider 2 voltage levels as 0 and 1. Generally, we consider 1 as 5V and 0 as 0V.

Q: Well what is 3.5 V then???? 😛
A: It is considered 1(actually anything greater than 2.5V will be considered 1)

• Analog circuits- We have signals which are varying in magnitude between the extreme values.
This diagram explains it:

### Some electronics components

Breadboard is a platform for quick prototyping of electrical circuits without using the soldering iron.

The horizontal holes on each side of the breadboard are connected together. Anything plugged into these holes will be connected together. The horizontal holes on one side are not connected to those on the other.
The first five and the last five vertical strips are electrically connected. The outer strip is usually used as 5V and the inner ones as GND. Usually the first five and the last five strips are joined by wire.

Some conventions that we usually follow.

• Single strand wires are used for connections.
• Connections must be tight.
• No wire without insulation must be seen on the bread board.
• 5V connections are in Red.
• GND connections are in Black.
• Other connections are in any other colour.

7805 IC
7805 IC is used for stepping down voltages. The 05 indicates that it steps it down to 5V.
See the image for the pin-out diagram given in the datasheet for the 7805T IC.
When one looks at it with bulge on it towards them, the left pin is the input of the input voltage, the centre ground and the right pin output of 5V.

Logic gates
These are very helpful in circuits. As the name suggests, they help to bring logic to circuits.
In the truth table, 1 means 5V and 0 means 0V.

Q: Now, why would I need them??
A: Imagine 2 smoke sensors connected to A and B. A fire alarm is connected to F and should go on(HIGH) when either of the 2 sensors are High. So what do you use here? An OR gate.
Imagine a situation where your sensors are highly unreliable ie they out of a sudden give HIGH output. What to do then? Use AND gate to make the alarm go on(HIGH) only when both are high.

They are available as ICs in the 74xx series.
Eg 6 NOT gates in this IC

Crystal Oscillator
Crystals are used to repeatedly generate signals with a constant frequency. The signals are nothing but alternate Lows and Highs. We need them to get a sense of time in circuits.
For instance a microcontroller needs to know for how much time to execute something. There, we need Crystals.

Capacitors– They store charge in a circuit. Well, that sounds useless? Since they are storing charge, they can be used to manage voltage fluctuations, since a capacitor tries to use up its charge and give out current.
Two types:
1) Electrolytic

2) Ceramic

These 2 types are different in the way they are manufactured and used. Electrolytic capacitors have an orientation ie +ve and -ve terminals while ceramic ones don’t.
And ceramic capacitors are usually available for low capacitances.

Potentiometers- Variable resistors
They are used to get voltages ‘divided’ using the principle of resistance being proportional to the wire length. For instance, you have a 5V line and you want 2.5V, set the potentiometer’s knob to 50%, and there you get it.

Diodes
These usually placed to stop reverse currents. Technically, there is a small reverse current, but practically, we just use them as reverse circuit protection agents.

There is a small voltage drop across diodes. We can usually model them as above.

LED
See the pin configuration for an LED. LEDs need 3V for powering up, and may get damaged at 5V. So always use a resistor in series(1kohm will be a good value to start with, change it if you want to modify the brightness)

Seven segment display
You have seen this in digital signboards, watches etc.
It’s really simple to use!! Every display line has a unique pin which can be powered to make it turn on and off.

MOSFETs and Transistors
MOSFETs and transistors are the heart of electronics around us.
Practically, they are employed in one fundamental application, as a switch, an electronically controlled one. Here, I mean that a signal controls the action instead of a mechanical switch action.

MOSFETs and transistors are different-
MOSFETs are used for heavy load applications.
They are current controlled ie the current given at the gate decides whether the switch conducts or no

Transistors on the other hand are current controlled. The current entering the base decides whether it conducts or no.

Timer IC
Timer IC is an IC using which we can generate ‘ticks’ of various frequencies, by just modifying the circuit.

For example, you can check out how to generate 1 sec ticks using it here- http://electrotech4u.blogspot.in/2012/01/one-1-second-time-delay-for-digital.html

There is a lot you can do with this IC, since you get a time element into your circuits using this IC. You can build clocks, timers, stopwatches.
The difference between this IC and an oscillator is that you can get any frequency with this, but with an oscillator, you can get only specific frequencies.

Opto-Coupler
This is an interesting circuit element, using this we can ‘isolate’ circuits ie separate High load and Low load circuits. It is another switch, similar to how Transistors and MOSFETs work, but the advantage that we get here is that the 2 circuits have no way to interact directly, since it works when light generated by plugging into one circuit drives the other circuit. This is called Opto-isolation.

Some tools that you will need:

• Wire stripper

• Digital Multimeter
Here is a list of basic functions that you can do with a multimeter- http://www.thomasnet.com/articles/engineering-consulting/digital-multimeters

What to do next?
The simplest way to start into electronics is to go in and do something, ‘get your hands dirty’.
So get started, build your first circuit.