Gas station without pumps

2015 November 27

Resistor assortment box

Filed under: Circuits course — gasstationwithoutpumps @ 11:36
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A few years ago, I bought myself a selection of 1% resistors, like the ones I have my students get in the applied electronics course (from DIYGSM through Amazon, though I have tried other suppliers since then, since UCSC purchasing doesn’t permit ordering through Amazon, even when their prices are the best).  The resistors come in sets of 10 on paper tape (cut from the long rolls used for pick-and-place machines), rubber-banded into bundles of about 50 different sizes.  After a while the rubber-banded bundles started to disintegrate, and I’d gotten quite a collection of loose resistors that were no longer on the tapes, so finding the resistor size I wanted was often a bit of a hassle.

For a while I stored the loose resistors by poking them into a block of foam, roughly sorted by value,  but that was no longer working well—it took too long to find out whether I had a resistor of the size I needed stuck into the foam.  So a couple of weeks ago, I bought a large number of 3″×5″ plastic zippered bags and a 4″×6″ index card box, and sorted the resistors by size into individual bags:

Box with about 120 different sizes of resistors, from 0.5Ω to 5.6MΩ.

Box with about 120 different sizes of resistors, from 0.5Ω to 5.6MΩ.

I was originally planning to use white address labels to put the size values on the bags, but the address labels did not stick to the plastic.  A different sort of label (like the ones sold for marking stuff on freezer bags) might work, but I just used a permanent felt tip mark to write directly on the bags).

I still have about 100 loose resistors to file away, which I’ll probably finish doing today. It takes a while, as I try to confirm each resistance value before filing it: both reading the color code and measuring the resistance with an ohmmeter. My Fluke multimeter is broken, so I’ve been using the DT-9205A multimeter that I reviewed earlier. I found out one reason that multimeter was cheap—one of the probes fell apart within a few weeks of light usage.  I bought myself some more cheap voltmeter probes on AliExpress, which work ok (though who knows how long they will last).  The new probes have very sharp tips, which is handy for probing surface-mount boards, but a bit risky for clumsy people like me—I’ve stuck myself with them a few times by accident.

The DT-9205A meter is rather awkward for reading resistance—it often takes several seconds to settle for a larger resistor, and there is no zero-function to compensate for the resistance of the probes when measuring small resistances.   The ohmmeter is only accurate to about 2% also (a 1kΩ±1% resistor measures at 984Ω on the 2kΩ scale), which is nowhere near as good as the Fluke meter I’m used to, nor the expensive meters at work.

The box and bags is much bulkier than the original rubber-banded bundle (maybe 4 times the volume), so I’m not going to recommend this approach to my students, but I think that it will save me some trouble in future (as well as letting me know when I need to re-order a particular size resistor).

 

2 Comments »

  1. If you search on Amazon for “Joe Knows” you’ll see his resistor and capacitor kits where the components are neatly organized. I bought both kits, and put my own loose resistors into his labeled bags.

    Comment by V John — 2015 November 27 @ 14:59 | Reply

    • I looked at assortments like those when I was first looking for parts for the class, but they all had relatively few resistor values and rather high prices. The assortments I have the students get have about twice as many values for about half the cost—but do get inconvenient to use after a while. So, for the students who will be using the resistors for only one or two quarters, it is better to go with the cheaper, more complete set, even if it is a little less convenient.

      I found it worthwhile to bag the resistors myself, since I already had the resistors.

      Comment by gasstationwithoutpumps — 2015 November 27 @ 15:09 | Reply


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