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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1mm pitch flex cable passthrough

By popular demand, the breakout/passthrough combination boards family now includes a 1mm pitch variant:

This version handles up to 30 signals which seems to be a practical limit of most 1mm FPC connectors. Each signal is numbered and brought to a 0.1 in spacing header for easy connection to your favorite logger/analyzer/scope. Continue reading