Yak Shaving: Resistors, 6500 of ’em, edition

Above: what 6500 1/4-Watt, 1%-tolerance metal film resistors (50 each of 150 different resistance values, ranging from 1 Ω to 10 MΩ) look like if you buy them from Taobao. That cling-film/plastic-wrap-wound bundle was roughly the size of an adult’s forearm, from elbow to wrist. Total cost: $USD 10.

For reference, Sparkfun’s Resistor Kit (COM-10969, current price of US $7.95) consists of 500 1/4-W 5%-tolerance carbon film resistors. Despite being smaller and offering a narrower selection for a higher price, it’s a great value in terms of the time you can save going with a prepackaged product versus slapping a resistor kit together yourself. I bought one a year back and would recommend it to anyone in the market for a 1/4-W resistor assortment.

Nevertheless, 6500 resistors! And double as many per resistance and at more than seven times as many resistance values as in (for example) the Sparkfun kit, for just a couple of bucks more? I was sold.

There was a catch. Remember what I just wrote about time savings making the Sparkfun kit a bargain? As shown above and in a very similar photo on the seller’s product page, the Taobao-bought lump-o-resistors would arrive “taped”, packaged in the long strips intended to be fed into machines that would pluck them, as needed, and do stuff with and to them. For example, in a video titled RT-86, Axial Lead Forming Machine lead former Prepares Taped Resistor, you can watch a machine take a length of taped resistors as input and kick out the resistors one by one with their leads bent ninety degrees and minus the tapes.

Unless I made something like the sort-of-accordion-fold cardstock packaging which Sparkfun employs for their resistor kits, trying to actually use my cheap-o resistors would be a pain. It was time to buy a couple of large sheets of beefy, 300gsm paper!

Using the Sparkfun resistor kit as a template, I designed its slightly larger cousin. Measuring, cutting, and folding like a demon, I cranked out six of these “books” altogether. As you can see above, each had six pages or panes onto which I could staple lengths of taped resistors. I’d already decided to cut each 50-resistor strip in half and, after printing out the list of resistances and marking off every second and third value, saw that I could get them all into three sets of two packets each if I attached (rather than the Sparkfun kit’s uniform five) seven, sometimes eight, and sometimes six 25-resistor lengths to each page:

The stapling step wasn’t as quick and easy as I’d hoped. Working vertically (staples running up-and-down rather than back-and-forth with respect to a page) yielded the best result but got trickier far from the short vertical edges (i.e. the first and last pages) of the book. Keeping the lengths of tape resistors in alignment so that one staple would pierce them all simultaneously turned out to be slightly problematic as well.

Was I done? No, I was not. Though all six packets looked identical from the outside, they actually came in three different flavors, seeing as how they contained three different assortments of resistors. I needed labels. At the same time, an awareness of the growing sunk time cost of this project had started to gnaw at my thoughts.

I worked up illustrations of the resistors’ color codes, grouped according to their position in the packets in which I’d stapled them, along with the corresponding numeric resistance values, so that I could know at a glance which resistance values were available in a given packet and on which page I’d find them without having to open that packet up.

At left-of-center above, you can see the cover of one packet. Columns of color-banded resistor illustrations represent the resistance values of the resistors stapled onto a single page (e.g. 1, 1.8, 2.4, 3.3, 4.3, 5.6, 7.5, and 10 Ω), with the top drawing corresponding to the topmost layer and the bottom to the lowermost layer, and column one being page one, column two being page two, etc.

Printed on ordinary paper, cut out by hand with scissors, and adhesive-taped onto the packet covers as haphazardly as possible, the labels were the final absolutely necessary step. Presto! I was finished.