Electrical Circuits Prof. Jennifer M. Blain Christen BioElectric Systems and Technology

Leadership in Engineering James West George Carruthers Patricia Bath

Units and Scaling

Units and Scaling Pico Nano Micro Milli Centi (none)10 0 kilo-10 3 Mega10 6 Giga10 9 Tera10 12

Units and Scaling What units do we use these words with? Meterslength Litersvolume Gramsmass Secondstime Voltsvoltage Ampscurrent Wattspower Ohmsresistance

Resistance Opposition to the flow of charge. When we measure resistance, we measure how much an object “resists” the electrons moving through it. We measure resistance in Ohms. We abbreviate this with an Omega, written like this .

Resistance Conductors have low resistance. Insulators have high resistance. Some things are in the middle, like silicon. Silicon is a semiconductor. We draw symbols for resistors that look like…

Resistance We can find out the resistance of an object with this formula: R =  x L WxH

How can we measure resistance? m V 9V Ohms Range

Sometimes, you try to measure something too big for me. I don’t know what to do, so I show you this. Try changing the range. If you are up to 2000k, and still get this…sorry!

Let’s try it out! You have 4 resistors. Write down the value of each one. Keep them separated, you need to know which one you are using!

Battery This is a 9 volt battery. Let’s check to see if it’s really 9 volts. We draw symbols for batteries that look like…or

How can we measure voltage? m V 9V Volts Range

Let’s make a circuit This is a breadboard. We use it to easily make electrical connections.

Hidden inside are electrical connections. The connections are made between each group of 5 holes. Like this…

Let’s check and make sure I’m not full of it. Turn the dial here, see what it says.

We are going to use wires. Remember, wires are conductors inside of insulators. We can use them to connect two things together. conductor insulator

Now let’s try to connect the battery and a resistor. Turn the dial here, see what it says. Battery

Turn the dial here; see what it says. Battery Let’s see how much current is flowing through the system. We need to make the current flow through the multimeter.

You might need to change the range. Battery Do this for each of your resistors. Let’s make a graph of the results.

Here is the symbolic way to draw this circuit. A

Series Circuits We can thing in “Series” if they are in a row.

What do you think happens if we put two resistors in series? Does this formula help? Let’s measure. Does the order matter? R =  x L WxH

You might need to change the range. Battery Let’s measure the current when we have two resistors in series

You might need to change the range. Battery

Parallel Circuits We can thing in “parallel” if they connect between the same two nodes in a circuit.

What do you think happens if we put two resistors in parallel? Does this formula help? Let’s measure. Does the order matter? R =  x L WxH

Let’s turn on a light Pick one of your LEDs (light emitting diodes). Place it in series with the smallest resistor. What do you see?

Put some lights in series. What do you see? Put some lights in parallel. What do you see?

Practical Question If you have lots of lights in series and one breaks, what happens? If you have lots of lights in parallel and one breaks, what happens?

What is a sensor? Thermometers Pressure sensors Acceleration sensors Light sensors Your multimeter You!

We have some sensors… let’s see what they can do

Photoresistor Put your photoresistor in series with your smallest resistor. What happens? Add your LED in series. What happens? Have you seen something like this in your home?

Let’s measure the current in this circuit.

Photocell Let’s try to measure this one. It’s pretty delicate, so be careful. Let’s move around and see what we get.

Tilt Sensor Let’s try add this into your circuit.

It all gets pretty complicated quickly. Now imagine there are about 2 billion devices on a computer chip. 2,000,000,000

What happens if we want to communicate over a long distance? Let’s try that! What happens to the signal?

Analog or Digital Analog signals are like the signals that humans perceive. They can have any value. Digital signals are like the signals that computers use. (Remember Boolean logic?) They can only have discrete values.

Analog or Digital Analog signals are elegant, but susceptible to noise. Digital signals are simple, and not very susceptible to noise. Which one would be better for long distance communication?

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