EO&N Really Cheap Decade Resistor Substitution Box - build and testing
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- čas přidán 5. 09. 2024
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After I published my Capacitor Leakage Tester in the form factor that fits to the row of test equipment under the shelf on my bench, many viewers suggested I add a resistor substitution box. I have had one of these in mind for some time, and considered building one using the conventional rotary switches. However, good quality 10-position switches are very expensive, so I decided to try a DIP switch version to see how it would turn out.
As it happens, I am extremely happy with the result, and have therefore posted the project in the 'share' section of PCBWay, the sponsors of this video. The link is below:
www.pcbway.com...
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Manuel, Nice project, easy to build and a great addition to a test bench.
Plus the added benefit of keeping PCB Way happy.
Suggestion for PCB way project: An IR proximity detector and speech synthesizer. You could put it behind a mirror and when your cat approached the mirror and saw its own image it would meow at him.
That’s quite an idea 😊 but I’d rather program the word “handsome” in for when it detects me 😊
@@electronicsoldandnew
Better yet use facial recognition software when it recognizes the two women in your life have it pronounce them as the fairest of them all as in snow white. Oh yes and when it Recognize you ask if you've taken out the garbage.
Two problems with that. 1) there would be constant war between the two, and 2) there’s nothing in it for me 😊
Something I always wanted to build. Using dip switches is an idea that never occurred to me, nice thought. Internal contact resistance of those switches turned out surprisingly good, I wouldn't expect that since they are usually meant for digital use. Instead of getting expensive 0.1% resistors, one can get like a 100 (or more) packs of 1% ones and choose the best 10 out of them. Great project!
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Good video. Just a note, regardless of how many resistors you switch in, the power handling is 1 Watt as they are in series configuration. Parallel configuration will give increased power handling. example... If you needed a 10 ohm resistance with a 2 watt power capability (and you did not have a 10 Ohm 2 watt resistor, you could use 2 20 ohm 1 watt resistors in parallel and the total resistance would be 10 ohms and capable of 2 watts. It's a nifty tool which I use for determining required resistances in design work. 😀
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An idea to ease up the selection, is to use 1 rotary switch to choose which of the 7 "resistor banks" , and then on the resistor bank itself you choose the value with the DIP switches. That way, you don't always have to move 6 resistor banks to zero, and the lifetime of the DIP switches will also extend. Grtz
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@@electronicsoldandnew , as i think of it, with the idea that i mentioned, you can only set the value of 1 resistor at the time, and not combined 2 or more resistors in series. Grtz
😊
Never had a use for a resistance box in my 45 years in electronics. I think it is more for use in a classroom situation.
Thanks.
Will do the same.
Thanks for sharing pcbway project
Pleasure
Hi Manuel,
nice project.
I would proposed to use the "10" position (instead of "1") to bridge out the resistor bank. With this you have a direct indication of the resulting resistance multiplier by the numbers written on the DIP switch...
That’s a great idea 😊
...and a few holes on each corner will be very helpful as well even if you use the board naked with standoffs or assembled in a box.
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BTW I highly advise put small curves on the corners of your PCB edges, makes them nice to handle (unless there's other design considerations)
Looks like a well thought out construct, thanks for sharing it! One question though, did you order the parts from a supplier like Digikey or Mouser? If you did, I know that you can make the BOM / List public at Digikey, ( not sure about Mouser), to make it a bit easier for interested parties to source parts. It might not be too hard to size that up to a project box, set in it with some stand off mounts, and then make a PCB with cutouts for the switches, no copper, and stencil it for your switches and raise it up a bit with some stand offs as well.
I got the resistors from Mouser. The switches from a local supplier.
Suggestion: increase the board size by say 1.0 inch in width & length & add holes in the 4 corners for stand off mounting? Another idea: break it into 2 boards, dips on 1 board and resistors on the other for ease of soldering. Connect the 2 with wires to keep the cost down or design for a suitable ribbon cable, although at increases cost.
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I would suggest at 1% tolerance resistance splitting the box in two halves. 0 to 9k and 10k to 9M. The 1k range was already negating the changes of the 0 to 9ohm range. Changing the larger three ranges to expensive 0.1% resistors may help a little. Better to have two separate outputs for two ranges, with the option to link together if setting the box(es) up against an accurate measuring device before use.
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The weak spot is the switches, as these types are not normally designed to handle much current. As 1 ohm, 1W = 1A
True. Low power only.
@@electronicsoldandnew i've seen a few smoked decade resistance boxes in the past, its so easy to forget.
Makes the hobby more exciting 😊 💨
A cheaper alternative (that seems easier to source) is a 2×10 pinheader and a jumper for selecting each decade. You can even get the jumpers with a small plastic tab for easy grabbing.
I thought of that, but then decided to go for this option. It’s a little more self-contained.
All my old test equipment is getting far too old, so I'm studying your videos, to build your designs, if that's ok with you.
No problem. Enjoy
If you would use a 1 watt only for every first resistor, you could use less for the others and still have a minimum of 1 watt
True. I though of that but then found that my supplier sells batches of 10 resistors at a lower price than the separately rated ones. That’s why I simply used the same types.
What is the lifetime of those dip-switches?
Each supplier should state the number of repetitions in their data sheets, so they will vary depending on the brand.
Cheap? No, this gizmo is ridiculous. Who is going to flip all those tiny switches? There's a good reason that resistor substitution boxes use thumbwheel switches.
You still gotta appreciate the effort instead of being so overly criticisive. I'm actually thinking of building one´.
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@@19janiboy96,, The main reasons I use an oldfashioned resistor substitution box at work (audio repair shop) are 1) for discharging power supply capacitors, where this device would almost certainly get burned up, and 2) for selecting the voltage-dropping/current-limiting resistor value to use when changing dial illumination and function indicator bulbs in vintage stereo equipment over to LED's, for which this *might* work. Frankly, my advice is to find an old resistor substitution box or decade box and maybe upgrade a few of the resistors as needed, in case any have drifted off spec or the wattage is a little too low. I use an old EICO substitution box that contains 2 rotary switches and one slide switch to select the ranges; with heavier duty resistors subbed for the lowest-ohms resistors, it works great. I haven't managed to burn the thing up yet, which for me is a minor miracle.🙃
I agree that the old boxes are great. I just wanted a few of these as I often need them for low voltage / low power applications.