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Arduino Programming and Electronics

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Project 1 & 2 Electronics explained

The measurements and symbols:

Resistance (R): is measured in ohms(Ω)
Current (I): is measured in Amps(A)
Electricity(V):  is measured in Volts (V)

The Math Equation:
Ohms Law:
Volts = Current x Resistance ( V=I*R)

This is a very handy equation.  You see  every piece of electronics has some sort of resistance and loss of energy.  This Means every part in your circuit uses electricity, gives off a little to a lot of heat and slows the flow of current/electricity.

When you decide to make your own circuits, you need to make sure you draw them out 1st so that you know how much electricity, power, current or resistance you need.  We don’t want anything blowing up in our face.

In project 2 you have 5 volts going into a resistor then an LED.  This means that the 5 volts should be used by all pieces somehow.  A regular LED uses up about 2 volts and uses about 20 milliamps or (20mA for short) in current (we usually get that info when you purchase them).  That means that the resistor should prevent/drop about 3 volts from going through. Otherwise the LED might go BOOM!  Knowing that the LED needs about 20mA we can assume the resistor needs to let through about 20mA as well.

Let’s do the math:

volts = current multiplied by resistance                (this is called Ohms Law)

3volts = 20mA * R        We know we want to turn on an LED.  We also know that the Arduino puts out 5 volts of electricity (5V). This means that out of the 5V the Arduino gives, 2 of it is used in the LED. So now we know the whole circuit has 3 volts left to play with. What we need to know is what size of resistor we need for the LED to work properly. If the resistor is too small, we could damage or blow up the LED.  Too big and the light may be dim or not light up at all.

so 3v = .02A * R

3v/.02A = R

150 = R so we need a 150 Ohm resistor


So what happened with a 300 ohm resistor, and what happens if we use a 900 ohm resistor?