Archive for the 'Hard Hacks' Category

Audio amplifier goodness

on 2007 July 22
in Hard Hacks and Teaching
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For the third and fourth activity in my TCOM 121.2 Telecommunications laboratory class, I asked the students to prepare a 200 gain (46 dB) audio amplifier using the LM386 with a bandwidth of 20-20kHz.

I required the students to perform simulations by creating a SPICE netlist. The learning curve required is very steep to meet a 1-2 week deadline for performing the activity. I pointed them to the sci.electronics.cad Usenet newsgroup to search from the SPICE .subckt model since the IC cannot be found by default in the library components of MultiSim or Electronics Workbench. There were sample demonstrations on how to generate the netlist and use the model file using LTSpice in the laboratory. My classes’ were very resourceful. To accomodate the steep learning curve, they were able to find an LTSpice symbol associated with the LM386 subckt model and was able to generate simulations using the conventional schematic capture method.

They implemented their audio amplifier circuits on a standard issued prototyping breadboard. Some were able to get gains of up to 190+ but others are still struggling to exceed a 3dB gain (hence the lab extension). After reaching the 43-46 dB gain milestone, they celebrated their accomplishment by playing with the circuit. Most of the students plugged the output of the amplifier to a speaker. Thus sounds were produced based on the frequency input in the function generator. One of my students, Dale Dy played a rendition of “Happy Birthday” using various frequencies from our signal generator and his groups’ LM386 Audio Amplifier:

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Changing Rubik’s Cube sticker labels

on 2007 March 15
in Hard Hacks
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It is an established fact the the sticker labels of rubik’s cubes deteriorate fast. For less than a year of using my newly ordered 3×3 cube from http://www.rubiks.com, 4 out of 6 faces were discolored. The “protective” plastic coating of the cube has a greater bonding strength with the colors than the sticker base. So as the stickers peel, so does the color. In the end, one will end up with a purely white cube.

I searched the Internet for methods on how to replace it. The most famous query from a Google search is to buy the official labels from rubiks.com. As a resident of the Philippines, this is the least feasible solution. I scoured various stationary, school and office supplies shops to look for the “official” (yellow, blue, green red, orange) but was not able to find all of the colors.

sticker_seal In order to have consistency among sticker labels, the best solution was to buy a clean sheet of sticker paper and print on it. These sticker labels were bought from National Bookstore along Katipunan Avenue. The yellow sheet is the clear acetate to protect the colors from fading in the future.

sticker_protection The next step is to print on the sticker labels. Using an HP Deskjet 3745 printer, a 600 DPI print of the labels were made. I also uploaded the sticker sheet so anyone can print the sticker labels. Measuring the dimensions from an official cube, each square label has a length of 0.625 inches. (Note: there are extra square labels in the sheet because I was also planning to recondition my Fused cube).
The next step before cutting up the labels is to insert the protective acetate cover. It must be laid out carefully. I think it is preferrable to use a roller-like device to lay down the sticker on the sheet to spread the acetate evenly. My attempt was a failure because I don’t have a roller-like thingie. What happend was very catastrophic. Bubbles formed on the sheet rendering my labels useless. Then off to the garbage bin the labels go.

Since the cube is useless without proper labels, I attempted a method using local materials available in a local supplies store here in the Philippines. I bought assorted art paper from National Bookstore. To efficiently (or hackishly) insert labels, double-sided tape was laid on the back of each color of an art paper sheet. Afterwards the art paper was cut-off according to the rectangular shape of the tape. Then I cut away square portions of the tape-art paper combination to be laid on the cube itself. Afterwards transparent adhesive (aka “Scotch”) tape was inserted on top of the art paper for protection. The result of the double sided tape - art paper - transparent adhesive tape combination can be seen below:

final_cube
Not bad eh? But after playing with my reconditioned cube for a while the labels started to deteriorate (again!). In my next reconditioning attempt, I will try to use clear nail polish for the protection layer and see the difference.

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