# Electronics Workshop (Stage 1)

1. Understanding Power, Current, Voltage, Charge, Energy
1. Multiplication stories and two hidden division stories

2 x 3 = ?

? X 3 = 6

2 x ? = 6

Distance = speed x time [speed rate distance/time]

Activity a: Take a few examples and ensure that everyone is comfortable with multiplication and 2 division stories especially distance, speed and time.

Difficulty in learning electronics – terms used interchangeably and too many units. We will simplify (we will have some gaps that we will close when we find something we can’t explain) and use Volt (V), Amphere (A), hour(h) and later ohm (Ω).

• Charge

The fundamental quantity we use in electricity is charge and this charge does work for us. We can imagine it like water – when we say the cellphone battery is charging or is charged we are actually using correct terminology. We are referring to charge. The rate of charging or discharging or the speed of how much charge/time is called current. It is like speed that we talked about.

Charge = Current x time

A  x h        = Ah

This means how many A for how many hours. 5 Ah means 5 A for 1 hr, or 1 A for 5 hrs, etc.

Do you know how much charge your cellphone holds?

Charge of my cellphone = 4000 mAh = 4 Ah

Activity b: Hotspot, GPS, Flashlight – estimate how much current do my applications and devices take. Use the % of usage.

What kind of batteries do you know?

Activity c: Do you know the charge of different kinds of batteries? [ Picture or batteries] What determines the size of batteries?

For the same kind of battery these are generally related to charge stored in them. Most cellphone batteries are the same voltage of 3.7 V so what matters is charge as we talked about.

• What is voltage?

Voltage is the ability to do work.

You can think of voltage as height from which water can fall as an analogy think of a battery as a water tank at a height filled with water – the water is like charge. The higher the tank the higher the capacity to do work.

Different devices say an LED that do some work act as a water wheel that rotate when water falls on them. Resistors act as pipes that limit how much water can fall from the tank.

Activity d: If you do not have enough voltage then even if you have a large charge in the battery you will not be able to even power an LED. Look at a C, D, AA, AAA, battery and see if you can light up an LED with just one battery?

• Power

What do we look for when we buy a bulb – power – generally called W we will use simplified units of VA. This also tells us that Power is related to both the rate of taking charge (current) as well as how much of work that the charges can do (height). This is why we simplify the units.

Power = Voltage x Current

VA

• Energy

But, we don’t pay for power we pay for energy i.e. not the power we are using now, but all the power we have used over one or two months.

Energy = Power x time

VAh      =  VA  x h

Power is the speed of using energy.

Activity e: Energy of bulb = 10 VA x 8 h = 80 Vah Estimate our energy consumption for the workshop or for home or for what they find interesting. Use a table of common items. Make your own example.

What will be my:

Light 20 VA

Fan 40 VA

Laptop – 45 VA

LED TV/Monitors – 150 VA

Heater – 2000VA

1.5 Ton AC – 1500 VA

Induction stove – 1300 VA-2000 VA

Fridge – 300 VA

Mixie – 600 VA

Small water pump – 400 VA

CRT TV – 350 VA

How much time do we use each of these for?

This also tells us that

Energy = Voltage x Current x time = Voltage x Charge

Can we now compare the energy of the batteries

Activity 6: Compare two batteries C type with 9 V.

1.5 V x 2Ah = 3 VAh

9 V x 300mAh = 2.7 Vah

Voltage is also Energy/charge i.e. how much energy a unit charge has or how much work can be done by a single charge.

Activity f: What kind of battery would you need if you were to run your home on inverter for 3 hrs?

• Introduction to LED

Outcome:

• A 9 V battery will not shock you unless you taste it.
• Children should know about voltage
• Children know that LED has an anode and a cathode (positive and negative) and is unidirectionaly (only turns on in one direction). It’s not a bulb.
• Approximate voltage across and LED
• What a resistor does.
• The principle of Kirchofs voltage law.
• How to use a multimeter to measure resistance and continuity as well as test a LED.

Activity

1. A 9 V battery will not shock you. Touch with your hands nothing happens. The current is too small to have any impact on us.
1. What is body resistance?
1. Measure with multimeter without conducting gel.
1. Apply conducting gel to measure resistance of body.
1. How does a Makey-Makey work. What kind of resistance does it measure.
1. Use a makey makey (can we operate it off a battery?) to go around and see what kind of objects conduct even a small amount of electricity or have resistance < 20 MOhm.
1. Can we light up an LED with a battery and our body? How about LED with a battery and some water?
1. Who wants to taste current? Only if you put 9V battery with wires on your tongue you can have some conduction. With a multimeter measure the tongue resistance. Is it the same as water resistance?
• Put the multimer in buzzer mode ensure the buzzer mode is working by touching the two leads of multimeter,take the meter and put on the materials you think that conducts and list the materials.
• If a connect a LED directly across a 9V battery it will give too much energy and the LED with blow. (Demo only! Not test it themselves.)
• I can use resistors to limit the current (how much electrons flow) through the LED.  Use a 1k resistor does the LED glow?
• Draw the circuit – learn the symbol of a LED, resistor and battery.
• Does the LED glow no matter how you connect it forward and backwards? No? LED only works in one direction. How do you know which way to connect the LED by looking at the LED. Is there any other test [Multimeter, Battery+resistor]. Looks which wire is longer is positive. If you look inside then you can see that the positive is smaller than the negative. [Give a point for children to be able to identify different ways to find out which terminal is positive.]
• Repeat water analogy for voltage – height, current like water flowing. More the voltage more the height and more the possible energy. We can limit the current with the width of the pipe and this is what resistors do. The take up some of the water pressure.
1. However, Current only flows if the path is complete. If there is a break anywhere it will not flow. In that sense it is not like water which will leak out if there is a cut in the pipe. No current can flow in air. The resistance of air even if we measure is infinite.
1. What is the current in the circuit with 1 LED and 1k resistor? The current of the LED and a series resistor is the same. There is no other path and the current flows through both of them as in case of a pipe and a tap (use water analogy).
1. Precautions while using the multimeter. Which mode for what. If we change the mode i.e. measure voltage, current, resistance. The voltage is the safest setting. The current and resistance is tricky. In voltage measurement mode the instrument is a high resistance so that it does not effect anything much. The current mode makes the multimeter a short and this could be dangerous.
1. Design or change the resistance till you get 10 mA through the LED. How will you know that 10 mA is flowing through the LED?
1. Ohms law (measuring the voltage across a resistor and dividing by resistance tells you the current). Use calculator if required. Measure a the resistance outside the circuit. Put it in series with the LED and the battery. Measure the voltage across the resistance. Divide voltage with resistance and get current.
1. Can we assume that most of 9V falls across the resistance and get 9V/10 mA=900 ohms? What is the actual voltage measured across the 900 ohm resistor.
1. How can you get 10 mA. You can assume that the LED is almost constant voltage when on and divide the restof the voltage by 10 mA to get the resistor you need.
• Breadboard and 7 segment displays

As circuits get more complicated you cannot just use your fingers and twist wires e.g. a component like a 7 segment display. We need to use a bread board for temporary connections and solder if we want something permanent on the PCB.

7 Segment display: To show how 7 segment display works

1. Breadboards and how they are connected. Small bread boards – 15 boards.
1. Use LED, battery and resistor to find connectivity and see how the board is connected.
1. Use some boards to show how the wiring is connected to there is no confusion.
1. With 7 segment displays CC (middle pin is grounded) – map the elements of a 7 segment display with the 8 input pins (one is a decimal point)
1. How to make it display number from 0 to 9. On paper. Make number 7 on the bread board.
• LDR (Light Detection Resistor) Just as light is produced when we pass electricity through a LED, light also has energy and can change the resistance of a photo sensitive device. This can be used for light detection using LDR.

Activity: Measure the resistor with a multimeter and see the value change as you shine more light on it. Use cellphone light, ambient light, cover it, etc.

• Transistor (as switch/amplifier)
• Understand the connections of a transistor. Measure it using multimeter. High hf rating indicates the correct direction to use the transistor. How to see how a transistor is connected. Have a page from its datasheet printed and laminated.
• We were able to light a LED with our body before. Can we use the transistor to light it brighter amplifying the current that was coming through our body?

Activity: From 9 V battery LED in series with a resistor (say 1k) at the collector of the transistor. I touch base and 9 V battery, does it light up. Can I tell it is brighter?

• Capacitor (storage and taking time to charge)
• Capacitor as a bucket if a battery is like a reservoir of charge. Charge and discharge a capacitor with a battery onto an LED. This is how LEDs are tested with limited power so they do not burn out.
• Capacitors charge and discharge based on the resistor connected to them. Possible to make a LED last longer if we connected a series resistor?
• Understand the symbol of all these circuits.
• Symbol of a battery
• LED
• Resistor
• Transistor
• Capacitor
• Challenges:

Challenge 1:  Light intensity is measured in lumens. Using the 9V battery and a limit of 10 mA. What is the brightest light you can make? You need to choose your LEDs (any number up to you in series or in parallel till there is one resistance connected to the battery). Measure your brightness with a lumen meter (and funnel to avoid ambient light).

Challenge 2: Make an instrument to measure the light intensity with an LDR.Cut off ambient light using a black tube (drip irrigation pipe). [Glue gun needed.] Measure the light that you made. Measure with one more group and see if it tallies with which one is brighter with the lumen meter.

Challenge 3: Make the first letter of three of your names. Once you complete ask for an oscillator to make the 7 segment display blink.

Challenge 4 a.: Design a project that can use a makey-makey to make a real-ife application.

Challenge 4 b.: Ask for a circuit that will make one LED light up with a switch and a transistor that will do the opposite.

Challenge 5: Synthesize your learning on a chart paper.