JANUARY 15, 2011 (See also Companion Blog )
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This is the same voltage regulator as Experiment 002, but with the addition of a switch and a light. There are also two commercial binding posts at the output side to connect to the external wiring. Not shown is the 15V transformer from an obsolete cell phone. This diagram is the part that I built.
Theory:
The circuit contains a switch, which I now know is called a STSP, or single pole single throw. When the current is turned on, the (yellow) LED will glow and the 7805 Voltage regulator will supply 5.0V. Some thinking was required to position the switch, and I decided to place it sequentially after the input capacitor. In my thinking, this means the incoming current is smoothed before it gets to any working components.
This makes the LED a more trusted indicator of current actually reaching the 7805 (voltage regulator) than placing the LED anywhere else in the circuit. The reason for chosing a red LED is that they are the most common, the cheapest, and use a very small current compared to blue, green and other colors.
Yes, I almost forgot the resistor, again. It is positioned so that any limit it places on the input current occurs where there is most likely to be a surplus. I also placed the indicator LED ahead of the 7805, because placing it on the output side would draw away some of the 5V and I didn't want that. The reason for the LED is also because I don't yet trust switches by themselves. I want to see the power light up the LED, not just a switch in the "on" position. I wonder where and how one would connect an output meter to this circuit. Is it supposed to be obvious?
Breadboard:
This is where I would include a photograph of the breadboard if I had a decent camera that could take such pictures.
Practice:
The store-bought LED switch turns out to be unsuitable for this circuit. It was permanently lit by a separate 1.7V supply and the LED did not indicate if the switch was on or off. I had to replace it with an ordinary toggle switch and LED. It took almost two hours to solder the first three components and I overheated several parts of the substrate (generic PCD board). There must be a better way.
Conclusion:
I need more practice on the soldering iron. And maybe to write some decent soldering directions that avoid the COIK syndrome, which I just used. COIK = “Clear Only If Known”. Since this circuit was fully functional on the breadboard in two different patterns (but same configuration), I put it on hold until I can reliably solder every joint every time, like the man on the video.
Updated January 17, 2011
Later it has been determined that none of the instructions on soldering contained a warning about the heated iron touching the substrate. Several of the diagrams showed the iron doing just that. Thanks a lot for nothing. Apparently touching the substrate is not necessary, as the heated solder will flow down the component lead and the solder flux will allow the solder to adhere to the circuit board. Testing is underway but that's the last time I trust a so-called bunch of experts.
Updated April 24, 2012
I built this circuit for demo purposes only, and quickly dismantled it to salvage the parts. The switch that worked was expensive ($3.60). Oddly, it costs extra to obtain a switch with the pins spaced so as to fit on a standard breadboard. That's a "duh", America.
Below is a comparison photo of the difference in how I've learned to solder, the two photos are about eight months apart. They don't represent this circuit, rather show the experience gained after ruining plenty of work by following the wrong directions.
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