DH: On the drive into work I was stuck in traffic behind a slow-moving Toyota Matrix. As my blood pressure began to rise, my mind started wandering into the movie, “ The Matrix” and the benefits that a virtual existence would offer to my current situation.  That cascade of thoughts led to a follow-on to your question from the last blog:  “How much energy is actually produced by the human body and how much real work could be done with that energy if it were harnessed?”  Could I, for example, produce enough energy to lift a Toyota Matrix and place it neatly on the roof of a nearby apartment building?

CC: You apparently spend too much time stuck in traffic, thankfully nowhere near me.  Although it is an interesting question.  In “The Matrix”, all humans were enslaved in a virtual world and their bodies were used, effectively, as batteries to support a machine world, right?

DH: Yep, so the question is whether the human body would be an effective source of power.  So, let’s take a look at this in “Mythbuster” fashion.

CC: Okay,  but just remember:  If the answer is yes, whatever you do, don’t tell the government!  There’s certainly plenty of energy contained within the human body – just the excess body fat on an average individual is worth about 4kW hours per pound! 

DH: Wow, I guess that makes you a really powerful guy!

CC:  I prefer to think of myself as “above average”.  And at an average of 17 pounds overweight per American, multiplied by 300 million of us, a nationwide exercise program could yield 20 billion kW hours, or the total amount of energy used by 200,000 of us in a year!  

DH: Ugg – are you suggesting a  national network of interconnected treadmills tied to the electrical grid?

CC: Why not – we could even call it the TreadNet!

DH: I think DreadNet would be more appropriate.  This sounds like work!    What could we do to harness the energy of the average American couch potato?

CC: Ah, brilliant.  Capturing the energy naturally expended in *your* day to day activities, eh? I doubt that would be able to power an LED for more than a few seconds…

DH: I heard that the military and NASA are investigating methods to capture electrical energy that the body produces naturally through heat, motion, flexing and stretching, compression, urine and body heat.

CC:  OK OK – let’s look at this more seriously. What you’re describing is an extension of the concept used by my “perpetual” (self-winding) watch. But let’s keep the urine out of this flow for now .

DH: Yeah, that makes sense – it’s tough enough to make a watch water-proof.  

CC: Let’s see, an average 2400 calorie daily food intake provides a person about 2.8 kWh of energy, minus the human basal metabolic energy required to “power” your body (heart, lungs, cells, etc.) of about 2.4 kWh, which leaves about 400 Wh for additional activity every day.

DH: Right, so theoretically, if that energy could be used with 100% efficiency I would have enough power available to be able to light 40 compact fluorescent bulbs for about an hour.

CC: Yes – you’d be the modern equivalent of Uncle Fester.

DH: Or, putting it more into perspective, I could drive your laptop for about 20-30 hours.

CC: Interesting…a perpetually-couch-potato-powered laptop!  But, unfortunately, you’d have no energy left to type!

DH: Sounds like a normal day to me! That energy would be provided by additional snacks!  Where’s that jelly donut?? 

CC: Until next time…

Cary Chin (CC): Welcome everyone to the inaugural edition of our low-energy blog, Absolute Power!  I’m Cary Chin, a Synopsys low power engineer and long-time computer nerd (Apple II through MacBook Pro, and a few PCs along the way) along with fellow Synopsoid engineer, Darin Hauer, a techno-geek in good standing (Apple IIc owner now sporting a home-built multimedia PC ), and we’re here to take an interesting and entertaining look at Low Power design, tools, methodology, and requirements.

Darin Hauer (DH): Hmmm.  That’s entertaining?  Wouldn’t getting a root canal be more entertaining than babbling on about low power?

CC: But power has become such a big issue in electronics design in recent years that the discussion itself is interesting.  And most people, even many engineers, don’t have a good basic understanding of power.

DH: you mean, you want to talk about how power is measured in units of watts, and how one watt is by definition one Newton meter per second (or one Joule per second), which makes power a measure of energy per unit time.  Electrically, power is the product of voltage (volts) and current (amperes).

CC: Exactly right.

DH: So I guess the next logical question to ask is: How many volts, applied across my temples, would produce enough amperes to have the same impact as reading your next line?

CC: OK, OK. Let’s look at this from a more “entertaining” perspective.  I’ve got an AM radio that can run for days or even weeks on a single AA battery. Why can’t I power my iPhone off of the same AA battery? 

DH: Well, a typical alkaline AA battery stores approximately 3 watt hours of energy, so ignoring losses in conversion, and assuming an average power consumption of 1 watt for an iPhone 3G in relatively high power operation (watching YouTube videos or surfing the web), that’s around 3 hours.  Of course, your mileage will vary greatly depending on your application..

CC:  Now that’s downright interesting!  And how about jogging? If I converted the energy I use to jog for 30 minutes on a treadmill – how much talk time would I get?
DH: That depends on how much you weigh…but on average a jogger expends a little over 100 calories (technically kilocalories – used from now on as simply “calories”) per mile.  So jogging at a pretty reasonable 6 mph for 30 minutes would burn about 300 calories of energy.  For me, since I am not a reasonable jogger let’s say 5 mph for 30 minutes which amounts to 250 calories of energy.  One calorie (really kcal) is about the same as 1.16 watt hours in energy terms (the conversion exercise is left to the reader), so that 30 minutes of jogging for most joggers could theoretically power your iPhone for almost 350 hours!!  For me, on the other hand you can reduce that to around 290 hours.

CC: Wow.  That’s either a testament to the inefficiency of mechanical work, or the incredible amount of work done by today’s electronic devices with very little energy!  No wonder the U.S. Postal Service is having problems.

DH: Now here’s what really sucks.  That same 300 calories that you just spent ½ an hour to work off on your treadmill can easily be undone by eating just one average-sized jelly donut!!  Don’t ya’ hate that!

CC: Yikes!  Keep that jelly donut away from me!  On second thought, if I could hook it up to my iPhone…

DH: Actually what you want to hook to the iPhone is a twinkie – it holds a charge for at least 1000 years!

DH & CC: Well folks, more educational and fun power-related tidbits coming in our next posting.  Until then, “Corrupt absolutely, read Absolute Power!”

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