New Resistance Substitution box


I recently bought a new Resistance Substitution box off Amazon. It is clearly a hobbyist grade piece of equipment, but it only cost 35 dollars. I used two meters and a power supply to get a accurate measurements of the resistors in the unit.

The substitution box was more accurate then I expected it to be, however it was not in the range specified by the manufacture.




set resistance voltage (v) current (mA) resistance percent accurate
set resistancevoltage (v)current (mA)resistancepercent accurate
1 0.2923 251.1 1.16E+000 16.41%
2 0.546 251.1 2.17E+000 8.72%
3 0.8018 252.3 3.18E+000 5.93%
4 1.0515 252.1 4.17E+000 4.27%
10 2.539 251.9 1.01E+001 0.79%
20 4.9877 251.9 1.98E+001 -1.00%
30 7.386 252.1 2.93E+001 -2.34%
40 9.665 251.9 3.84E+001 -4.08%
100 23.12 251 9.21E+001 -7.89%
200 18.27 93.6 1.95E+002 -2.40%
300 18.332 62.5 2.93E+002 -2.23%
400 18.361 46.7 3.93E+002 -1.71%
1000 28.50 28.94 9.85E+002 -1.52%
2000 28.53 14.36 1.99E+003 -0.66%
3000 28.54 9.54 2.99E+003 -0.28%
4000 28.55 7.19 3.97E+003 -0.73%
10000 28.56 2.86 9.99E+003 -0.14%
20000 28.56 1.43 2.00E+004 -0.14%
30000 28.56 0.952 3.00E+004 0.00%
40000 28.49 0.716 3.98E+004 -0.52%
100000 28.53 0.2861 9.97E+004 -0.28%
200000 28.53 0.1444 1.98E+005 -1.21%
300000 28.56 0.0974 2.93E+005 -2.26%
400000 28.56 0.0735 3.89E+005 -2.86%
1000000 28.56 0.0307 9.30E+005 -6.97%
2000000 28.56 0.0166 1.72E+006 -13.98%
3000000 28.56 0.0118 2.42E+006 -19.32%
4000000 28.56 0.0096 2.98E+006 -25.63%


I opened it up to see what it looked like on the inside.  I thought the build quality was good for such an inexpensive device. Fasteners go though the front plate, to a PCB, and then into a threaded cylinder. Screws also enter the threaded cylinders from the other side, though the case.IMG_0807


The PCB is straight forward. There is simply an array of switches and there the corresponding resistors are right beside the switches.


I burned the 100 ohm resistor on this board, when I was not paying attention. (pure negligence)


The high value resistors are a bit different. It appears two resistors are placed in parallel. This looks goofy to say the least.



The other side of the board has a nice green color to it. It is clear that this is a single sided board, which I don’t see to often anymore. Large though-hole components make single sided board possible.


I can’t be certain, but it looks like this board was hand soldered. The amount of solder, and way it sticks to the pads leads me to think it was not wave soldered. I can defiantly see finger prints on the finish of the board.

IMG_0799This will be a very useful piece of equipment when I start testing DC-DC converters, and need an constant sink for my test supplies.



dirt bike carburetor (yamaha ttr 125)

We have a Yamaha TTR 125 dirt bike, and the carburetor leaks gas continuously. Rather then trying to rebuild the carb, we planned on just replacing it. New aftermarket replacements are very inexpensive (around $45). I don’t normally work on dirt bike fuel systems, so this was kind of new for me.

The new shiny carb

It was relatively simple to replace the carburetor. It took a second to insert the throttle, and choke cables.

Old carburetor ready for disassembly

Below are two diagrams that show the internal workings of a carburetor.



I took the carburetor apart just to see how it works. While it was in pieces, I snapped some photographs.

The float bowl is removed, and the two floats are visible


The throttle slide, and spring


totally disassembled

Ham radio

I now hold a amateur radio technicians  license. My call sign is KM4OGC, and it wont expire for 10 years.  This allows me to transmit on the 10 meter, 6 meter, 2 meter, 70 cm , 33 cm, and the 23 cm bands.

Amateur radio bands, color coded.

I am going to have to remember my call sign KM4OGC  (Kilo Mike 4 Oscar Golf Charlie). I have a radio ordered on and on the way. It is a baofeng dual band 2 meter and 70 cm.  I am exited for it to arrive, and start contacting repeaters.

The local radio club, w4nja, was very friendly, and made it very easy to take the exam.