panasonic toughbook

2 Articles

An Open Source Electromagnetic Resonance Tablet

January 14, 2026 by 18 Comments

Drawing tablets have been a favorite computer peripheral of artists since its inception in the 1980s. If you have ever used a drawing tablet of this nature, you may have wondered, how it works, and if you can make one. Well, wonder no longer as [Yukidama] has demonstrated an open source electromagnetic resonance (EMR) drawing tablet build!

The principle of simple EMR tablets is quite straight forward. A coil in the tablet oscillates from around 400 kHz to 600 kHz. This induces a current inside a coil within the pen at its resonant frequency. This in turn, results in a voltage spike within the tablet around the pen’s resonant frequency. For pressure sensing, a simple circuit within the pen can shift its resonant frequency, which likewise is picked up within the tablet. The tablet’s input buttons work in similar ways!

But this is merely one dimensional. To sample two dimensions, two arrays of coils are needed. One to sample the horizontal axis, and one the vertical. The driver circuit simply sweeps over the array and samples every coil at any arbitrary speed the driver can achieve.

Finally, [Yukidama] made a last demo by refining the driver board, designed to drive a flexible circuit containing the coils. This then sits behind the screen of a Panasonic RZ series laptop, turning the device into a rather effective drawing tablet!

If tablets aren’t your style, check out this drawing pen. 

Continue reading “An Open Source Electromagnetic Resonance Tablet” →

Reviving A Stubborn Laptop Battery

January 19, 2014 by 42 Comments

We’ve all gotten bored of certain toys and left them on the shelf for months on end. But what do you do when this prolonged period kills the batteries? Well if you’re [Andrew] you take apart the battery pack and bring it back to life!

[Andrew] picked up one of those Panasonic Toughbooks awhile back and although it’s hardly a top of the line laptop specs-wise, it does have some pretty cool features: it’s shock-proof, splash-proof, and extreme-temperature-proof. It even had a touch screen before touchscreens were cool. Despite its durability, however, the laptop was left to sit for a bit too long, and the battery pack no longer accepted a charge.

[Andrew] quickly disassembled the battery pack and began measuring the cells with his trusty multimeter, assuming just one cell had gone bad. Curiously though, no cells reported 0V. What he did find was that each cell and sub-pack reported 2.95V, which is 0.05V below the “safe operating limits” of typical lithium ion cells. Continue reading “Reviving A Stubborn Laptop Battery” →