The Lightbulb Came On When the Lightbulb Came On

Sitting on the floor with a battery, jumper wires with alligator clips, a small light bulb, she traces the circuit in the picture on the book. She'd seen me put the circuit together and now she wanted to do it herself.

It all started with a well intentioned mistake. She cares about making sure her mom and I understand when she's cleaning something up. Getting cooperation in picking up her room, or putting away toys is as big a challenge as it can be for any five year old, but sooner or later things start to click, and it begins to come automatically. In this case, she was very proud of the fact that she was taking the batteries out of their packaging and putting them in a smaller box.

Because I don't want the house to catch fire from a shorted battery, I had to explain why putting batteries in a box like this was a bad idea. A couple of years ago, I got a kit from Radio Shack that introduces kids to electricity, circuits, etc. She knew about this kit, and got it out to ask me how a battery works. For the next hour she discovered how batteries work, how motors work, how a lightbulb comes on, and that some parts only work in a circuit one way, and she even did Morse code with a piezo buzzer.

That brought us to the moment when she could do it all by herself, help the electricity make a loop so the battery could do some work.

She just had to hook the alligator clip to the bulb and...

Presto!
The electricity in the battery made a loop and the light came on.
She of course couldn't wait to show Momma.

Finding Obsolete Parts: Furthering This Idea of a STHR

In a recent Post, I put forward the idea of a Strategic Thru-Hole Reserve of parts commonly found in kits made in the mid 90s to today. There's been some good feedback about this, so the next step is to discuss what comes next. I envision a website where people go to share what they have and what they need. Let's say I need a 2SC2166. I should be able to search for the part, select a person with the part, and contact that person to make some sort of arrangement to acquire the part.
Sound about right?

"Death to the Resistors!" update A

So here's the story so far,
I've got five resistors, nominally valued at 100 ohms.  I'm going to execute a plan to test their power rating.  I've learned a lot about testing standards, and resistor power ratings, probably more than I wanted to know.  Apparently there are some rigid standards, and exacting practices people go through to test and certify parts for particular applications.  Some of these tests are daunting to say the least!
Test a resistor for 10000 hours?
Meh, not going to happen for me.
That's just one of the current requirements a manufacturer has to meet for the current round of MIL-SPEC testing.
I'm not going to MIL-SPEC certify these resistors.  I am however, going to take some suggestions offered to me from the good folks on QRP-L.
From Mike WA8BXN:

Sounds like you want to do some destructive testing. How will you relate that to what should be their normal power rating?

Rather than doing a destructive test, it might be interesting to find the power that takes the resistor above its rated temperature.

Another test that would be interesting is to measure resistance after cycling power on and off. This is related to checking the next day but is different because I would run through more powered cycles.

What ever tests are done should also be done with resistors of known good quality and specifications.

Good suggestions!
I'll devise a series of tests, first thing I have to do though is rig up a test jig to measure the actual value of the resistors!  My first attempt was a bust due to 9v battery issues on my digital VOM.  Once I took care of that, I realized it can be pretty tricky to measure the values of the resistors.  They have this thing about holding still.  I don't think they like going into the holes that I stuff them in.  I'm pretty sure the hot tin/silver amalgam I apply to them upsets them too.
I've only ever had one capacitor blow up on me though... long story, but I now never apply power to a rig with the top off without first putting on my safety glasses, and yes, I had safety glasses on that time!

Death to the Resistors!

Chris, K4FH, has been gracious enough to give me 5 of his 100 ohm ebay resistors to test for their actual watt rating.
I would like to solicit comments on the criteria people would consider 'good enough' during this test.
They are marketed as 1/4 watt, 5% tolerance resistors, from ebay.  I will try to identify the manufacturer and I will try to acquire a datasheet for them.
Here's the procedure I will use to test them:
1.  measure resistance. The measurement shall consist of two readings from my elcheapo centech digital VOM; 1 taken as close to the epoxy body of the resistor as possible, and the other as close to the ends of the resistor leads as possible.  Any significant difference in measurement will be confirmed using an analog meter.  "Interesting" results will be posted to QRP-L and my blog before I do any experiments on the resistor, and that resistor will be isolated.  I will take these measurements at the following times:
   a) before doing any testing
   b) immediately before testing
   c) immediately after testing
   d) next day after testing
2.  Label resistors, Resistor 1-5, based on their resistance from measurement A, 1 being lowest, 5 being highest.  In the event of a tie, the first resistor measured gets the lower number.
3.  Test the power dissipation of the resistors.  I will probably only do one test a night over the next couple of weeks.  I usually get home from work sometime between 04:30 and 05:00 UTC, and spend about 1.5 to 2 hours 'winding down'.  I try to be in bed by 06:00/07:00 UTC (2am local time whether daylight savings or not).  That gives me about 1 hour to test resistors each night.  During the day, I watch my kids, so I won't be able to test them outside of that time frame.  Here are the tests:
    a) full bench supply for 1 hour: I'll post the exact model number and voltages read before the test, but a 100 ohm resistor across the 13.8 VDC terminals will output  1.9044 watts and draw 138 mA of current, if I done did the math right. I haven't measured the terminal voltage of the supply in a while, and this will be as good an excuse as any to figure out howthe list high quality my 10 year old supply is.  Voltage will be measured every 5 minutes during the test.  After the test, I will publish my results via QRP-L, and my blog before continuing.
    b.) I will set up a series/parallel resistance circuit.  The series part will consist of a lump parallel section, and a variable series section.  The parallel part will be 5 resistors wide, the test resistor being one of them, and is switched in and out of circuit with another resistor of equal resistance and higher power rating.  The circuit will be constructed in such a way that the total power handling of the circuit is at least 4 Watts without the inclusion of our test resistor.  Each of the tested resistor will be tested by varying the voltage available to the parallel section until the resistor fails.  When the resistor fails, it will be switched out and the 4th resistor in the circuit switched in, the voltage across the fourth resistor will be measured and used to calculate the power dissipated.

Circuit theory: because resistances in parallel share voltage and resistances in series divide voltage, it's possible to use a series/parallel circuit to produce a measurable voltage at the terminals where a test resistor is located.  This measurement can be used to record the power dissipated by the resistor at the moment of failure. 

My circuit and calculations will be published on my blog and QRP-L before testing for peer review. 
    c.) After each test I will publish my results within 12 hours of testing. 


So there you have it, Death to the Resistors!
thanks everybody!