It isn't expected that the Pot would be something that would be adjusted while running is it? I would assume that it's more or less "static" given a given frequency, yes?

With that kind of luck, maybe you should start picking Lottery numbers! 

I assume that your S3 is still mining using the pool that you want, with the credentials you want? The classic attack on a miner is to just point it at a different pool and let it coniynue to mine, for somebody other than the owner.

With $.09 power, you have several options, all of which will produce an operating profit (produce more than costs in electricity). The choices then are how much do you want to spend for the initial purchase.

Antminer S3 (used), S5
Spondoolies SP20 (used)
Avalon 4.1 (probably too high priced, though quiet)

Some other Antminers (e.g. S4+) and Spondoolies boxes (all used) might work, though you might well need something better than 120VAC for power.

What kind of power connection do you have? Is it the customary USA 120VAC outlet or what?

I'll put up the nightly figures from bitcoinwisdom:

Bitcoin Difficulty:    47,589,591,154
Estimated Next Difficulty:    49,754,771,543 (+4.55%)
Adjust time:    After 308 Blocks, About 2.0 days
Hashrate(?):    362,890,187 GH/s
Block Generation Time(?):    
1 block: 9.2 minutes
3 blocks: 27.8 minutes
6 blocks: 55.5 minutes

Price: $231

Definitely going to be positive, though may well be below 5%.

The difficulty adjusts every 2016 blocks. If things are stable, that works out to 14 days. If the hashrate is increasing, then it will finish the 2016 blocks in less than 14. The sooner those 2016 blocks are finished, the sooner, and greater, the difficulty will increase. In a sense, difficulty rises faster (< 14 days) than it falls (> 14 days). The halving as I recall will happen after 410,000 blocks are done, and we around block 380,000? You can confirm these values with some Google research.

So you will see roughly 2 difficulty changes in a month, so 5% works out to 2-3% for a change. You can see the historical values, though you are right that the rate of increase has been slowing. 2014 was a brutal year for difficulty increases, and it probably won't be as brutal this year. So far it's been fairly benign.

A lot of this will be driven by the price of Bitcoin, and I have no idea what actually drives that. One thing I am pretty certain of is that difficulty follows price. If the price increases, difficulty follows suit. If we see $300-400 BTC price, a whole lot of hashrate will "appear" in short order. It won't be all new gear, some will be older less profitable gear that's just powered off. I think there is a chunk of currently "cold" hashrate, waiting for a better BTC price.

Looks like you are going to try and turn some of that hardware on, after it's been sold to you.

Have you worried about "cooling" at all yet? I never ran a stick miner that didn't get pretty warm in dead air.

Good result, regardless of the hashrate.

CONGRATULATIONS!!!

Just couldn't leave it at 150 MHz, could you?   

It all depends on your personal situation. If you plan to have a miner within your normal, residential living space, you probably can't tolerate a hot noisy miner which requires more than 120VAC for power.

Assuming you are interested in reducing your running cost, or maybe turning a profit, then your electricity costs will play a huge role in your selection. If your electricity cost is over about $0.15 for a Killowat hour, then your electricity costs will exceed what you make in BTC while you are mining.

As with most things in life, it depends.

I won't bore with the usual response of "There is no such thing as free electricity". That point will eventually be made to you one way or another. It will most certainly not be "virtually unlimited" as you mention.

I will however try and temper your expectations a bit. In case you haven't visited the website:

https://bitcoinwisdom.com/bitcoin/difficulty

While it's a bit dense, if you were to put together a 1 Terhash (i.e. 1000 GH) miner, it could earn about $17 in a week, for the next week. The difficulty is looking to go up before your weeks is done, and your income will probably be reduced by about 3%. This of course assumes the value of BTC doesn't change (in terms of USD). Nobody can accurately predict what will happen to the difficulty every two weeks for the next year, since it's entirely dependent on what all the miners in world do in terms of adding or removing hashrate. While the last 3-4 months have had a little increase in difficulty, I expect that situation will not last for more than another month or two. We know that a variety of manufacturers are working on next generation ASIC, and they will almost certainly manifest in terms of hashrate increases.  If you scroll down on the above website, you'll see past difficulty adjustments and when they happened. There is also a little calculator you can use to get an idea of how quickly your mining hardware will, or won't, get paid off.

And just to top it all off, sometime in the first half of 2016, your income stream will get cut in half. That's when the block reward, currently 25 BTC in a block, gets cut in half to 12.5 BTC. This happens for everybody, and it can't be stopped. It's all baked in the Bitcoin mining protocol.

While it looks like mining is "printing money", it really doesn't print it very quickly, and most attempts to speed it up are negated by difficulty increases.

If you already know all this, then you can just dismiss as cynical old guy.

What kind of AC infrastructure will you have for this "free" power?

I am guessing you don't care about noise?

Remember that an inefficient power supply will add to your cooling load, since the difference is heat.

Sidehack or Novak might have to weigh in here, but I think the table was derived by measurements from sidehack. The U3 connection is that it identifies to the driver/miner software as a U3, even though it obviously isn't a U3.

That's how I understand it, but I've been wrong before as my wife likes to say.... 

Go back up about 8-9 posts, and you'll find a table of frequency/hashrate. That's for one chip, which is what this stick has.

If you were to increase the clock frequency to 400 MHz, you should expect the power draw to double. You might also find that the fan attached to the U3 is NOT able to handle the increased heat.

Proceed with care in attempting to "overclock" your U3.

Does anybody know if bfgminer supports the U3? It's been over 9 months since I worried about USB stick mining, and haven't kept up with support in bfgminer.

I too found the Zadig/Windows interaction to be quite frustrating. I ultimately went to the Raspberry Pi realm, which I found a bit more stable.

I assume you have tried taking one of your "new" (i.e. recently arrived) S5's and swapped it in place of a working S5? You just want to make sure that the S5 is functional, and not a broken PSU.

There was previous S5 fan noise thread quite a while back. One member mentioned that he used a dead 120mm fan as a "spacer" between the regular S5 fan and the metal plate of the S5. . He cut out the motor, blades, motor support, and just retained the 120mm shroud of the fan. He noticed a reduction in noise just using the stock fan. While it looked almost like two fans stacked at the one end, it supposedly worked well at reducing the noise.

This was essentially the spacer mentioned above, and about 25mm "thick". I think the idea is that the air flow is a bit more "organized" by the time it actually hits the heatsink. That's my simplistic understanding.

In case you guys aren't looking:

https://bitcointalk.org/index.php?topic=1086882.0

Lot's of good info on S5 temperatures, hot spots, and enclosing an S5.

While my memory may be equally bad, I too think Rolla Missouri. When I attended college back in the 70's, it was University of Missouri, Rolla (one campus of the University of Missouri system at the time). The acronym was UMR. It's since renamed itself to something more glitzy. At the time it was only about 4000-5000 students, though it graduated about 800 engineers a year.

This is kinda what I felt yesterday. While I agree that this is likely "more than just variance", I didn't have a good way to find the most proximate cause of the increase. Is your choice of KNC based on an instinct, or something more concrete?