Building Electronic Circuits using Breadboard
For those who are starting with the experiments in Electronic world, this is an easy activity to understand how to build real circuits (connections) from the circuit diagram. But before we go for complicated circuits, let’s start with a simple “Lighting up a LED” lesson for learning how to make connections on a breadboard.
What is a BREADBOARD?
A breadboard is used to make temporary circuit for testing or trying an idea. You don’t need to solder the components so they become re-usable afterwards.
How to make connections on a breadboard?
The breadboard has many strips of copper beneath the board that connects the holes as shown (i.e. short circuited or on a same potential). The upper blue lines are not connected to the lower ones.
A node is a point in a circuit where two components are connected. On a breadboard a node is the row & columns of holes that are connected by the strip of metal underneath (as shown above, the blue lines are only depicted on a part of breadboard but the pattern runs across the whole breadboard). These strips connect the holes on the top of the board that makes it is easier to connect the components. Connections between different components on a breadboard are formed by putting their legs in a common node.
The long top and bottom row of holes are usually used for power supply connections.
Now we begin with lessons:
LESSON1: Lighting up a LED
Circuit elements required: Two LEDs, resistance, power supply (DC) between 6 to 24V
If you light a LED without a resistance, a large amount of current will flow through it and damage it within a very short time period.
Now, add a resistance of 390Ω. Now it’s safe to switch on LED and here it glows…
Maximum current that can flow through a LED is 20mA, if there is 9V across the terminals. A voltage drop of 2.5V (approximately) across the LED (yes, LEDs too have this much voltage drop).
R= 7/(20 *10-3) = 350Ω, (so we can choose a 390 Ω resistance that is standard easily available in market)
If we choose a resistance of higher value, the LED will be dimmer.
In practice we can use a resistance of 1kΩ in series with an LED for 12 V (or less) without much thinking tough you may sometime find it very dim.
- If you are connecting LEDs in series then calculate the voltage drop across the resistance after considering the forward voltage drop of all LEDs & choose a suitable resistor.
- You should never attach LEDS IN PARALLEL. If you wish to do so, attach resistance in series with every LED.
REMEMBER never connect LEDs directly and always add resistances as explained.
Lighting up LED using a 5V filtered power source from 9V supply that is generally needed for microcontrollers & some other ICs for their working.
This is achieved by using an IC for converting a high DC voltage source (generally 12V – 9V) to 5V DC source.
Q: If we need a 5V supply for microcontrollers why don’t we use a direct 5V power supply?
- Those power sources that claim 5V supply, if you check the voltage across there terminals, you will hardly find it to be near 5V, it will vary around 6-8 V. If we use such a power source it may damage your microcontroller, but it can be used with resistances in series to get optimal 5V.
- If we are making an autonomous bOt with two dc motors that operate on 12V, then we generally use a single power source. We can use a DC-DC converter IC for converting the input power to 5V output for the microcontroller Vcc and other ICs like H-Bridge etc.
The IC used for this is of series 78xx. All the ICs nearly perform same function but with little variations like maximum input voltage, temperature (it can withstand), current rating, etc.
Some other ICs of this family are: LM7806, LM7808, LM7824, LM7809A, LM7812A, LM7815A, LM7818A, etc.
Here we are using a L7805CV dc-dc converter (the common name of such ICs that are used just as transformer to generate a higher or lower voltage from an input).
Always remember that ground should be common for a given circuit and all GND ends should be joined together (as shown below). This should always be kept in mind, otherwise unexpected things may happen.
Now, after we have a 5V power supply. If we check the voltage with a multimeter we will find something between 4.8- 5.2V but it is actually the average value. If you try to observe the voltage with an Oscilloscope you will see a lot of noise on the 5V rail.
What is ripple?
The noise is called the ripple. This is very bad for an electronic circuit & you will not get desired result if there is a lot of noise in the Vcc and it is therefore advisable to use a filtering cap for a (ripple free) good output. With no filtering caps, we will find a noise of 200mV. The filtering caps are used to remove this noise from the output.
What’s a filtering cap?
The filtering caps are polarized capacitors used for removing noise from the output. Polarized capacitors are the one which have polarity & should be fixed into circuit (check Basic Eelectronic Components to know more).
Capacitors cannot deliver their stored energy instantaneously. Large caps (10uF & 100uF) store more energy, but they react more slowly. The smaller the capacitor, faster it can deliver its stored energy. If there is a large power output power dips for 10-100ms, a big cap (100& 1000uF) will help to ‘hold up’ the falling voltage. A smaller cap (0.1uF) will help suppress higher frequency noise & shorter power dips (noise in the 1us to 100us range). Therefore, 0.1uF caps are located near the microcontroller to help with short bursts, where 100uF and 10uF caps are used on the power rails.
We are using a 100uF (one-hundred micro farad) on the input side and 10uF on the output side (as shown in the figure above).
NOTE: These two capacitors filters are commonly used in the power distribution system.
These filtering caps used in this case are (100uF/25V and 10uF/10V). The value of the voltage that is recommended to be used should be slightly greater than the voltage needed.
If we accidently supply power with wrong polarity sense (i.e. you give 5V to GND & 5V to Vcc), then unexpected things may happen and the microcontroller may get damaged.
Therefore to protect the circuit from such accidents we can add a diode as shown in the figure above. A diode lets the current flow only in one direction (in the direction of arrow) & the current that can flow in reverse direction is negligible. The diode will block the current in the reverse direction and protect your circuit.
For reverse protection we generally use a 1A 1N4001 diode that is really inexpensive. A diode has a maximum rated voltage, keep this in mind for choosing a diode, (for e.g. if I choose a 0.1 A diode but it 1A current from the circuit, it will get damaged).
Though it may not seem necessary to use a diode but it is a good practice. You will always find one in a development board.
We can also add a LED, to avoid using a multimeter again for checking the power input/output of the circuit. It will help saving a lot of time in debugging. If the LED doesn’t light up then unplug the power supply immediately and check the circuit.
You can also add a switch as shown in the figure below to control the power supply.
Hope we are ready to play with electronic circuits and understand those big circuit diagrams better.
If you are not familiar with the electronic components and their symbols read the following tutorial Basic Electronic Components.