Everything is a voltage

OK, well not everything, obviously.  However, our lives are permeated by electronics: not just cell phones and laptops, but garage door openers, coffee pots, earbuds, traffic lights, thermostats.  Understanding how voltages control just about everything we use was quite the “light bulb” moment for me.  

First off, what exactly is a voltage?  It’s easiest to think about voltage as a hill – sort of like the hill we were biking down in the last post.  Electricity is carried by electrons.  An electron can be thought of as a ball (a very tiny one, of course), which wants to roll downhill.  The bigger the voltage, the bigger the hill that the electrons will roll down.  In fact, you may have heard the term “ground” used in reference to electrical circuits.  Just as an actual ball falls to the ground when dropped, an electron will “fall” towards the voltage ground.  A battery does the work of carrying that electron to the top of the hill and pushing it down.  So an electron pushed “downhill” by a 9-volt battery will carry more energy than an electron pushed by a AA (1.5-volt) battery.  

Electrons travel around a circuit towards the voltage ground, just as a ball rolls down a hill.

Using electrons for electricity requires pushing lots of them downhill.  Or, more accurately, through an electrical circuit.  When pushed through a circuit that contains a light bulb for example, the energy that the electrons carry can be used to produce light.  When a signal of one type is converted to a signal of another type, we physicists like to say that it has been “transduced.”  In the case of the light bulb, we transduce electrical energy to light energy. 

Transduction can happen in both directions.  Instead of converting electrical energy to light energy, as in a light bulb, there are sensors that go the other way, converting light energy to a voltage.  A lot of new-ish cars now have such sensors in order to detect light and determine if it’s dark enough outside to require headlights.  The sensor then sends a voltage to operate a switch that controls your headlights.  And you can convert more than just light energy to or from a voltage.  A microphone transduces sound energy into a voltage.  This voltage is sent through cables, possibly amplified, and transduced back to sound energy at the speaker.  Sound energy to voltage, and back to sound energy.  

All this talk about converting light and sound energy reminds me: biology makes use of voltage signals too.  In fact, you can think of your eyes, ears, fingers, tongue, and nose as transducers.  Your eyes take light in, and transduce it to a voltage.  This voltage signal is sent via your optic nerve (think electrical wires) to your brain, where the voltage signal is interpreted as an image.  Your ears are just like the microphone – they take pressure waves in the air and transduce it to a voltage which your brain interprets as sound.  This insight changed the way I experience live music.  The energy in the singer’s voice is converted many many times – sound to voltage at the mic, back to sound at the speakers, to ear drum vibrations, to neuron signals – all before you experience it as music.

All of your senses are mediated by voltages.  Everything gets converted first to a voltage in order for your brain to process it.  It works the other way too.  Let’s say you wanted to run, bike, or swim.  Your brain sends voltage signals to your limbs, causing your muscles to contract and your limbs to move.  A triathlon wouldn’t be possible without voltages.  

Another useful concept in electrical circuits is the switch.  We are all very familiar with the light switch.  But switches are so much more ubiquitous in everyday life than just the light switch.  Anything with an ON/OFF button has a switch, sure.  But the left and right mouse click: those are switches too.  So is every button on the TV remote and every key on your laptop keyboard.  Switches allow us to control the flow of electricity.  A voltage will push electrons around a circuit only when the circuit is a complete loop, as in the light bulb cartoon below.  

 

A switch is used to control whether a voltage pushes electrons around a circuit.

Using a switch, you can also use voltages to push electrons over long distances in order to send messages.  This is the premise of a telegraph.  At one end of a telegraph line is the sender.  He or she presses a switch in a sequence of long and short pulses to encode the message.  That switch closes a circuit, allowing electrons to flow all the way to the receiver.  At the receiving end, those electrons are used to turn on a light bulb in the same sequence of short and long pauses.  While watching the light bulb flicker, the receiver decodes the message.  (Instead of turning on and off a light bulb at the receiving end, a speaker or buzzer was often used – accounting for the familiar beeping noise we associate with telegraphs). 

Telegraphs are ancient history though.  Who cares?  Well, the principle of sending messages hasn’t really changed a lot since then.  The message you send in an email is transduced first by your keyboard to a series of voltage pulses.  These pulses are sent to the computer, were they are again transduced – they can be converted for saving on your hard disk, to pixels on your monitor, or sent along again as voltage pulses across the internet through the cables provided by, well, your cable company.  At the other end, those voltage pulses are interpreted by the receiving computer and again transduced to pixels on a screen to display the letters of the message.  

Between switches and transducers, you can interact with and control just about anything.  That’s why I was so excited about this week’s project at www.donorschoose.org\sciathlon – “Electrical Inventioneering.”  I’ve chosen to highlight this classroom in Illinois because it will get high school students using their own hands to learn how signals can be converted to and from voltages.  They will be building electronic circuits using a really cool circuit board called Arduino.  The Arduino is all about transduction: “Arduino senses the environment by receiving inputs from many sensors, and affects its surroundings by controlling lights, motors, and other actuators.”  I believe the chance to build such circuits will change the way these students view the gadgets they use every day and may even spark ideas for how we can use technology to improve lives.  I hope you can help me make this happen!  As always, thanks for your support.