Optical mouse, the old way

Today’s topic is somewhat unique- a vintage optical mouse, made in the days when it was not very trivial. It’s not like you can just slap a camera in and have it take pictures to figure out where things move. In the old days you had to actually design it, maybe even using some 2N3906 and 555 timers as we’ll find out. Let’s start with unboxing (pardon the masking tape holding things together)

Vintage find

Vintage find

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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).

OLYMPUS DIGITAL CAMERA

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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

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.  

Datasheet: