UV led's

It is rather bad for the sewage system though. Copper salts in effluent waste can stall solid waste decomposition in septic tank systems.

I dunno about trial-and-erroring to that design. How they were made was surely refined over time, but the concept is nature inspired...when you squint your eyes you're less likely to go blind, so someone built a widget that is effectively a set of surrogate eyelids that squints for you.

Seems to me more like some Inuit long ago had a flash of insight and once the insight arrived by whatever mechanism, they hacked out the first prototype in a day, and it more-or-less worked first time.

I think I recall reading that it's believed in some cultures wheels were used in children's toys before they realized they could be scaled up to build war chariots, but did humans trial-and-error their way to the fundamental design of a wheel? Did they build square wheels first or were the first wheels also round? Has any archeologist ever found a square wheel that predates all round ones?

So can most chemicals that kill bugs, unless they decompose fairly quickly into something harmless (which means they are only a short-term treatment).

Instead of bleach, you could try sodium peroxycarbonate which generates nascent oxygen as it breaks down into fairly harmless sodium carbonate. It is one of the major ingredients of clothes-washing powder, so you might try experimenting with that. It is also a very safe way of breaking down sewage in camping toilets and doesn't need any special disposal facilities, unlike that vile blue stinking liquid that is often used.

You could try sodium bicarbonate, which is quite effective at cleaning refrigerator interiors and may well work on the bugs you are trying to remove. It certainly won't pose a health hazard or damage the sewerage system if it is only used in moderate quantities.

I heard that Microsoft re-invented the wheel but their first model was square. Next year they are going to bring out an improved model which is triangular, so it only gives three bumps per revolution instead of four.

Hexagonal, to one significant figure.(*)

Cheers

Phil Hobbs

(*) making pi equal to 3.

Well, lah-di-dah. ;)

Cheers

Phil "Mid-century ceramic tile, thank you" Hobbs

When I was a kid, in geometry class, I figured that one could take the average diameter of a square, divide by the circumference, and get pi.

It seemed to work.

I've done the Sewer Tour in Paris and San Francisco. Both were interesting. SF smells much better.

You've seen the cabin. Perfectly dreadful 1960's pastel ceramic tiles everywhere. At least there are no bunnies or butterflies.

For the right definition of "average diameter", sure. ;)

As a child, an older acquaintance of mine tried calculating pi by working out 22/7 to many decimal places by hand.

English amateur mathematician William Shanks worked out pi to 707 places by hand (527 places of which were correct).

When asked how long it took him, he said, "Three years of Sundays." Yikes. (Of course I shouldn't talk--I've been writing the same book since 1994, off and on.)

Cheers

Phil Hobbs

But you don't have the fun of looking for where Jean Valjean carried his prospective son-in-law. ;)

Cheers

Phil Hobbs

Pretty sure I'm still less posh than you lot, though. ;)

Cheers

Phil Hobbs

Oh dear. Post some pictures.

We just re-did our kitchen at home; long story.

We used off-white rectangular subway tiles, which have been in fashion for 100 years or so.

If you want to design a lot of stuff, it's best to have a short attention span.

What were we talking about?

Electronic design.

Oh, okay. Does this count? I made it old-fashioned for the benefit of the group's user base!

That first stage is super-bootstrapped. Gain would be huge if the cathode resistor were bypassed and there was no feedback.

(You *could* buy an opamp.)

You could have included some p-channel tubes.