I recently picked up a Withings scale because I am tracking as much data as I possibly can while using the Perpetual Progress protocol. It is neat and everything, but it has one massive design flaw. It is a Wifi scale that uses AAA batteries. Suffice to say it chewed through a set of batteries in 1 week. There is no option to use a power adapter at all. Horrible, horrible design decision. Fortunately, it was pretty trivial to hack.
UPDATE: A few hours after posting this I got an email from the CTO of Withings. He checked out the debug logs, and determined that the batteries that shipped with the scale were defective (voltage logs at the bottom). According to Withings, the batteries should last 6 months on a good set of alkaline batteries.
The prompt and thorough follow-up by the CTO just shows how well they’ve thought out this product. I don’t want this to be a full review, just a quick hack post, but I have to say the product is exceptional. All the setup and out-of-box stuff was fantastic. The Withings scale is a great product.
Nonetheless, I am sticking with AC power.
First thing you need is a power adapter or wall wart. You’ll need something that outputs roughly 6 volts, and I’m just guessing on current requirements but 500mA should be more than enough. I happened to have a Nokia phone charger laying around that was rated at 5.7V and 800mA. Perfect. If you don’t have things like that laying around, make a trip to Radio Shack and buy a 6V wall wart.
Next step was to determine the polarity and which of the battery contacts mattered. The way these things work is that the metal tabs are just connect different ends of the batteries to each other in series. So only 2 matter, the negative and the positive connected to the device. They’re marked on this image:
Next up you’re going to strip the wires and determine the polarity of the wall wart. I can’t think of any way to explain how to do this without using a voltmeter or at worst an LED. Then again, if you don’t have a voltmeter around the house you probably aren’t trying to hack your Wifi scale to add a power adapter.
I could have made this next part a lot more complicated, but I am a fan of getting things done, not coming up with impressive complex solutions. All I did was strip the wires, insert them behind the batter tabs, and pop the batteries in. This pushed the wires against the case so hard, that there is no way they are going anywhere.
Since the batteries are there for no purpose but to hold the wires, and you’re leaving the middle 2 batteries out, they aren’t even part of the circuit. I added a couple pieces of tape to keep everything in place, but they are very very snug anyway.
I would really hope that the rev 2 of this scale would have a jack for a power adapter. Using batteries for something like this is inexcusable.
[DBLIB] DBLIB_IE_PWR_DEBUG : “6.49V (6.15V, 2.77Ohm) 97%”
4 days after you packed out the scale
[DBLIB] DBLIB_IE_PWR_DEBUG : “6.23V (5.78V, 3.89Ohm) 77%”
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