This is my present for my love for this Valentine day. I was always want to build a circuit on a paper craft, but I don’t like to mess with the wiring. Until I found a solution: the Circuit Scribe conductive pen, which allows you to make an electronic circuit on a paper ! But to build a practical circuit (not just to turn on a LED), this mighty guy will do the heavy work: the Silhouette Portrait. It’s basically a 2D plotter and cutter, just mount the pen in there, load the circuit traces and click the “Cut” button. The circuit is designed using Altium Designer, which all components are surface-mounted and the trace width is set as 0.6 mm.
The circuit schematic
Several MOSFETs are used to drive a large number of LED, as well as to sense a touch switch. Luckily all the pins are fitted in a 8-pin microcontroller. All the components are mounted on the paper using super-glue. The circuit is powered by a 3 mm-thick 240 mAh Lipo battery, with a tiny converter to boost the voltage from 4.2 V to 6 V. Why? Because the ink has resistance too ! The actual VCC voltage at the chip is only 5 V and is less at the further LEDs. This is the first time I have to deal with the trace’s length and width in a low speed circuit. As a result, some paths are thicker than the others for this reason.
Battery and boost converter
I found a perfect cover-up for the battery, the “hoy di nha” wolf! Funny huh? The last step is to write and load the code. It is done easily, just treat it as an typical Arduino board. One PWM channel is used to drive the red LEDs, three digital pins for other LEDs and one ADC channel for the touch switch. With everything ready the whole card is completed in 3 days (with fails, replacements, re-test, re-design, repair… and other frustrations), but finally it works!!!
Behind the scene
And that’s how the clip is made, with an Xperia Z2.
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