Apple Watch: Moore's Law need not apply

▼ Jean-Louis Gassée over at Monday Note has an interesting article talking about how cameras used to last for decades back in the analog days, while they're obsolete within a year or two now that they're digital. And how the same thing is about to happen to the watch: an old mechanical watch will keep doing its thing for decades (I'm assuming some upkeep here), but not so much for an Apple Watch:

There’s no carrier subsidy for the AppleWatch. That could be a problem when Moore’s Law makes the $5K high-end model obsolete.

I'm not so sure Moore's Law is going to make the Apple Watch obsolete within just a few years. Moore's Law states that the number of transistors in an integrated circuit (a computer chip) doubles every two years, and perhaps doubles in performance every 18 months. However, a smartwatch isn't limited by the number of transistors or the speed of those transistors, but rather, the battery powering those transistors. And despite the transistors in mobile CPUs getting smaller, they don't seem to be getting that much more power efficient at undemanding tasks.

This is a list of battery capacities for most iPhones, along with the number of hours they'll play audio and the amount of power playing audio thus takes:

• iPhone: 5180 mWh, 24, 216 mW
• iPhone 3G: 4255 mWh, 24, 177 mW
• iPhone 3GS: 4514 mWh, 30, 150 mW
• iPhone 4: 5254 mWh, 40, 131 mW
• iPhone 4S: 5291 mWh, 40, 132 mW
• iPhone 5: 5472 mWh, 40, 137 mW
• iPhone 5S 5966 mWh, 40, 149 mW
• iPhone 6: 6914 mWh, 50, 138 mW

(Source: Wikipedia List of iOS devices.)

Since the iPhone 3GS the power an iPhone uses to play audio has been between 130 and 150 milliwatts. So for an undemanding task like playing audio there has been no improvement to the iPhone in five years. (Caveats apply; I'm looking at the big picture here.)

As such, I'd be very surprised to see new watches released every year that significantly improve on the previous model's technical specifications. I think the Apple Watch is going to be like the Apple TV or Airport Wi-Fi base stations in this regard: significant updates happen rarely, but modest under-the-hood hardware improvements are rolled out once every year or two without fanfare and with little impact to the user experience.

I am going to be very upset when the 2016 model adds GPS, though. If anything, the watch v1.0's Achilles heel is going to be lack of GPS.

Permalink - posted 2014-12-08

Power use of bluetooth vs Wi-Fi vs wired audio on the iPhone 5

▼ With all this bluetooth audio going on, I wondered: how much power does playing back audio over bluetooth use? So I tested this. The tests then snowballed as I got curious about audio over Wi-Fi, or having bluetooth and/or Wi-Fi on when the phone is idle. All the tests were done on an iPhone 5 with a freshly replaced battery under iOS 7. The results:

• Playing audio through the headphone jack, airplane mode, background app refresh off. In 7:59 the battery went from 50% to 34%, 2% per hour.
• Playing audio through the headphone jack, Wi-Fi off, bluetooth off, background app refresh on. In 8:04 the battery went from 50% to 31%: 2.4% per hour.

So in airplane mode, you should be able to play audio for 50 hours and with 3G enabled but not Wi-Fi or bluetooth and no background app refresh to trigger CPU and network use, it's a bit over 40 hours. I guess this also means that just running the 3G radio uses 0.4% of the battery per hour, so the standby time of an untouched iPhone 5 would be 250 hours. (A week and a half!)

Now let's add some bluetooth and Wi-Fi:

• Playing audio through the headphone jack, Wi-Fi on, bluetooth on, background app refresh off. In 8 the battery went from 44% to 23%: 2.6% per hour.

With these settings, you'd be able to play audio for over 38 hours, three hours less than with Wi-Fi and bluetooth off. But what if we start actually playing audio over buetooth?

• Playing audio over bluetooth, Wi-Fi off, bluetooth on, background app refresh on. In 8 hours the battery went from 72% to 45%: 3.4% per hour.

Now we're down to 29 hours of audio playing. So if you really only use your iPhone to play audio and you need it to last as many hours as possible between charges, using the headphone jack certainly makes a big difference. But you'd have to charge your bluetooth headphones two or three times before the iPhone runs out of juice! In normal use, this is more than good enough to use bluetooth for audio when that's convenient and not worry about the iPhone's battery.

However, there's another way to stream audio from an iPhone: over Wi-Fi.

• Wi-Fi streaming, bluetooth on, background app refresh off. In 9:55 the battery went from 89% to 65%: 2.4% per hour.

So streaming audio over Wi-Fi uses the same amount of power as playing through the headphones. Who knew?

Last but not least, what's the impact of having Wi-Fi on on the standby time when the iPhone is idle?

• Standby, bluetooth on, wifi off, background app refress off. In 8:49 the battery went from 23% to 18%: 0.6% per hour.
• Standby, bluetooth on, wifi on, background app refress off. In 9:44 the battery went from 18% to 11%: 0.7% per hour.

So with just 3G and bluetooth on the standby time would be a week and with 3G, bluetooth and Wi-Fi on six days. In other words: having bluetooth on uses an extra 5% of your battery each day, and bluetooth + Wi-Fi 7% per day.

Please note that I did every test only once and the accuracy and precision of the battery charge indicator are limited, so this is just a rough estimate, don't be fooled by the fact that there are numbers behind a decimal point. But I think the overall conclusion that you can simply leave Wi-Fi and bluetooth on is a pretty safe one.

Permalink - posted 2014-10-21