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Apparently it uses 1.5mW at 1V.

You can get batteryless radios. Crystal radios (which don't necessarily contain a crystal) get all their power from the radio signal, and they're scarily simple. During the second world war foxhole radios were built out of a razor blade, a pencil, some wire and a set of headphones (instructions: http://www.bizarrelabs.com/fox...) Prisoner of war radios used coal

AFAIK, however, the much lower energy VHF signals for FM isn't capable of running an FM decoder, and probably not an earpiece either.

I wonder if a modern crystal earpiece could usefully pick up low-power AM transmissions from a cellphone in your pocket without spamming everyone around you with radio waves?

American Science and Surplus has a nice collection of used microscopes (and lots of other very cool stuff) at very low prices. Their inventory changes frequently.

Celestron makes a $50 webcam-like (USB) eyepiece camera for telescopes, but it works nicely with microscopes as well. Celestron also sells inexpensive mechanical microscopes.

For thin specimens or slices, you want a compound microscope. For stereo images, you need a stereomicroscope (a.k.a. dissecting microscope). The two have very different designs. The stereomicroscope has two identical objective lenses next to each other, like the two lenses in a stereo digital camera. Unless you need very high magnifications, you can do pretty well with any of the "toy" USB devices that has a built-in webcam and a single magnifier lens (e.g. RadioShack zOrb for ca. $40).

You can build your own compound microscope, which might make a great project for a 7-year-old: http://www.funsci.com/fun3_en/ucomp1/ucomp1.htm

Finally, you can make a Leeuwenhoek microscope (the original microscope design, from the 1600s) with a single spherical lens of 2-3mm diameter and some ordindary household materials. You can make the lens if you have a torch or Bunsen burner, or get one from Edmund Optics (edmundoptics.com). Lots of how-to sites on the web, e.g. http://bizarrelabs.com/micro.htm (one design on this site uses a drop of water as the lens).

Sounds like a fun project.

Soldiers in the (first) 2 World Wars used to make radios out of rusted razors, a safety pin (a cat's whisker diode) and a coil of wire (to tune)

http://bizarrelabs.com/foxhole.htm

However, the kind of tolerance is *probably* already present in the DLP chips. The forces that the spring is subjected to were carefully calculated, and the technology has been in use since the 60s. You could probably take a look at the older types of DLPs and compile evidence that a large amount of cycles won't harm it.

Caveat: I am not a micro-mechanical device engineer, but I follow developments. I figure micro-mechanical devices will need control systems of some sort someday.

~Sticky
/It's all about temperature, pressure, and friction.

One of the coolest things I saw in middle school was a cloud chamber, in which the science teacher placed a small sample of Uranium.

Once the environment was right, we could see very tiny smoke trails shooting off from the Uranium sample. What we were seeing was the effects of the alpha and beta particles leaving the Uranium sample.

It's a shame that our society is growing so paranoid that amazing things like this will probably not be possible to do in schools anymore.

Bizarre Labs has some great stuff. Lemon batteries, crystal radios, electro-magnets, leyden jars. Even plans for Tesla coils and radioactive cloud chambers are there.

This does beg the question: What are the basic principles that need to be covered. Here are some that I would imagine are important:

Magnetism

Electromagnetism

Basic Circuits and electron flow

Photon Simultaneity

... well maybe not that last one, success rates are still pretty low. You might have to build up to that with a few simple explanatory topics.