Nexus 5 power switch replacement

Another older repair I am getting around to post. This time it’s a Nexus 5 phone that acquired an interesting habit of getting stuck in a random reboot loop. One moment it’s working fine, next it’s stuck in a boot screen with Google logo, then buzzes and reboots to the same thing. After a bit of Googling around, I realized that the likely culprit is a power button getting stuck. To confirm, I’d smack it a bit and watch the phone exit reboot loop and work for a while. That smacking was satisfying but not sustainable if I wanted the thing to survive. So back to ebay we go. I suppose Mouser/Digikey were also an option if I felt like desoldering the original, measuring it and then combing through all similar parts to find the fit. Instead I let other people do that.  Most sellers had an exact replacement switch, but one claimed a new and improved one. It also looked a bit better so for $2 shipped I grabbed one. The typical title for these is “4mm Power On /Off Volume Switch Button For LG Nexus 5 D820 D821 Optimus L4 E440”.

Tiny thing

Tiny thing

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FrankenPad part deux

Hot on the heels of a touchpad swap in my “new” Thinkpad T440P, come the next two upgrades: backlit keyboard and an IPS display. I shall call this machine Frankenpad as it’s rapidly deviating from the original configuration (20AWS series).


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A tale of buttons

It all started innocently enough.

I finally decided to replace my 6 years old Thinkpad X200 with a bit more modern used T440P. More power, better battery life and all the other modern goodies were all things I was looking forward to. Unfortunately I also knew that for the 44x series Lenovo changed the design of the trackpad to a single piece clickable square. No more beloved buttons, so easy to use with the trackpoint. Not a big deal- plenty of people reported using the newer design of the trackpad off a T45x series to get those buttons back, so I figured i’ll just swap it in. The laptop came in, and I tried really hard to like the trackpad as is. No go: total lack of feel, constantly pressing RMB instead of LMB and a very annoying clicking sound  heard in the whole house. It had to go!

Look ma, no buttons!

Don’t mess with success, Lenovo!

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Part of the week: TI TPL5111

Stumbled on this interesting part from TI recently


TPL5111 solves a typical problem in low power wireless systems- things need to be off most of the time, and wake up periodically to transmit. The usual solution is to pick a microcontroller that can stay asleep in low power mode at a few uA, then wake up on RTC timer. That works most of the time, but sometimes even that is too much standby power. Imagine a system for example that has to work from a small coin cell for 5-10 years. Each uA of sleep current is an 8mAh a year. So in 10 years, 80mAh is wasted. (A typical CR2032 battery for example starts with only 220mAh)

TI’s solution is a timer that can stay on while drawing 35nA. Once set with a single resistor for a particular time interval, between 100ms  and 2 hours, it turns power on to the system, waits to hear back from the micro via “done” pin and then turns things back off. TI even provides a handy table of resistor values vs timer settings. Not bad for $0.45@1k, plus there are many other scenarios such an almost zero power scheduler may be handy.  



Watchdog Water Alarm teardown

Today we have a somewhat vintage teardown. Even though you can still buy this Watchdog BWD-HWA Water Alarm in home stores and online, the design itself probably goes quite a few decades back as we’ll see below. We’ll also learn a few things about low power design. Rumor has it these last forever on a nine volt battery!

Front view

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