Perspectives of a Canadian in the Old/Deep/New/Geographic South: This is where I ramble on about nothing in particular and post a few nice pictures.
Things I do for fun
My amateur radio license in the FCC ULS database changed from General to Amateur Extra this afternoon, so now it’s really official!
I put in the application for a vanity call sign, so in a few weeks I should be getting on the air with a shiny new and cool call sign.
Whee!
Still looking at radios and deciding what I want to get.
I decided to explore a method for measuring the capacitance of an unknown capacitor using the capacitance measuring capability of my DMM. It has a range of 7 orders of magnitude (pF to 20 μF).
The total capacitance of capacitors in a parallel arrangement is just the sum of the capacitors.
C = C1 + C2 + ...In series, the inverse of the total capacitance is the sum of the inverse of the capacitance of each capacitor.
1/C = 1/C1 + 1/C2 + ...The total capacitance will be less than the smallest capacitor in the chain.
By placing the unknown capacitance in series or parallel with a known capacitance and measuring the resulting total capacitance, it becomes a pretty trivial matter to calculate the value of the unknown capacitor. Of course the total capacitance still has to be in the DMM’s measurable range.
In theory, either arrangement should yield the same result. I thought it would be interesting to see what kind of results I would get.
Armed with breadboard, some jumper wires and my DMM, I grabbed 5 capacitors that my DMM could measure. One capacitor served as my known (0.47 μF, which measured 0.442 μF according to the DMM). The other four would be my “unknowns”. Each of them was a 1 μF cap with measured values of 0.961, 0.0.964, 0.972 and 0.996 μF. By measuring the total capacitance with the capacitors in series or parallel arrangements, the unknown capacitance is easily calculated and can be compared with the measured value.
I ended up with some interesting results, but probably not terribly significant in the grand scheme of things.
Calculating the capacitance of the unknown capacitor in series with a known capacitor underestimated the measured value by 3%. Calculating the capacitance of the unknown capacitor in parallel with a known capacitor was more accurate, overestimating the value by just 1%.
I suspect most likely source of the difference between the two methods is due to stray capacitance in the breadboard or maybe in the DMM. It’s like having adding extra capacitor in network. With differences this small, I’d consider the two methods to be pretty much the same (as would be expected).
Some of the other “unknown” capacitors I have are pretty big, but armed with enough knowns and putting them in a suitable arrangement of series and parallel layouts, I should be able to bring the total capacitance down to something my DMM can measure, and be able to see just what the unknowns are.
Part 3 will probably see me exploring another method. I may need some more components for that though.
Digital multi-meters have come a long way since I first used them. Back then all they gave you was voltage, current and resistance. My new DMM also has a temperature probe, measures capacitance and tests diodes and transistors.
During the process of sacrificing and dissecting a couple of old laptop power bricks, I’ve harvested a number of components, including transformers, inductors and capacitors.
Testing a capacitor to see if it’s still good is pretty simple by checking the resistance. Low resistance is bad, very high/infinite resistance is good, high but not very high is leaky.
I’d also like to know what the actual capacitance is, and how it compares to what’s printed on the capacitor. The capacitors I harvested are outside the measuring range of my DMM, so the easy way would be to just buy a capacitance meter to test them.
I don’t always do things the easy way though, especially when there’s an opportunity to learn something new. I’m pretty sure I can come up with a workable method to measure the “mystery” capacitors.
Finally found some time to sit down with all the bits and assemble a second Morse code key using the supplied schematic. At first it didn’t seem to work, but after checking through everything I found one of the speaker wires wasn’t fully inserted (short lead). After I fixed that, it buzzed at me when I clicked the button! The button is the clicky kind, so it’s not that well suited for doing Morse code, but it works! The buzzer was also a lot louder than the kit, which I later discovered was due to me forgetting a resistor between the final capacitor and speaker.
The next step was to make it light up in addition to buzzing. Spent some time looking at the schematic for a place to insert an LED that I didn’t think would make it go poof or fry anything. Put in a red LED and connected it to ground, pushed the button and it lit up! Then I decided to try a second green LED in series with the red, and they both lit up! Success!
A variable resistor instead of the fixed resistor in front of the speaker I think should give me some volume control, so I’ll try that next. I need to get one first.
Now that I’m an Extra class ham, thoughts have turned towards thinking about what kind of HF radio I want, where to put it, where to locate the antenna and other fun things like that.
The past week or so I’ve been surfing the Ham Radio category on ebay just to see what kind of equipment people put up for sale there. I’m a bit of a sucker for older/vintage equipment, so while there are lots of shiny new radios available, my attention tends to get drawn to the older stuff. I don’t know how practical it would be for me to own and use older gear, but they do look pretty cool. Maybe by the end of the year or early 2013 I’ll have my own rig set up.
There are BarcampCHS sessions to prepare for, a garage to clean out (to make room for more workbench space) and ham shack space to think about. Thanksgiving will bring the #WATwitter (Worked All Twitter) QSO Party where I’ll be getting on the air with Connie/NR4CB to get Twitter/ham contacts. Work us on HF and you’ll get a 2-for-1 QSO!