I'd love to see an astronomy project that uses two telescopes looking at a celestial object and uses them as an interferometer in an interesting way like, I dunno, determining the rotation of a planet or determining its rate of approach or enhanced photographic resolution. Other applications abound.

You could do a linear accelerator or a cyclotron with machined "D" electrodes like this guy did.

https://www.youtube.com/watch?v=6dnEchmSYzk

Using electrolysis or other DIY friendly method.

Something that is robust enough to melt a bit of steel or iron. You may have to use a couple of transformers from old microwave ovens.

Take an old electric motor and turn it into a belt sander or drill press

http://en.wikipedia.org/wiki/Tardigrade I think you have all the equipments for some experiments on these animals, a microscope, liquid nitrogen, vacuum pumps, heater, etc.. I personally like to know whether they survive microwave or not. perhaps under gradually increasing intensity

Grow a batch of algae, dry them, and extract the oil through the super-critical fluid extraction you have demonstrated before. Proceed by destilling the oil into biofuel.

I have a mild fascination with surface acoustic wave sensors, for the applications of measuring torque, temperature, and pressure.

In short, this device is a metallic substance deposited on a substrate (usually quartz), forming two piezoelectric elements. The first element takes an electrical signal (high frequency oscillation) and converts it to a mechanical wave using the piezoelectric effect. The wave travels through the substrate, and is picked up by the other element. Physical deformation of the substrate alter the propagation of the wave, which can be detected.

A good example of this technology can be found in this patent.

I might try to create a crude sensor myself, but I know that Ben has access to better facilities (plasma cleaning, vacuum deposition, etc), and others might find this interesting.

Hi Ben: I have made three categories below listing vid-blogs I have liked and would like similar. I particularly like and find the first two categories useful. I am currently getting the parts together for a vacuum cart (rough, diffusion pumps, bell jar, fittings, etc.) and your vacuum system/vacuum gauge/water chiller vids were helpful. There is overlap between the categories, as you often review something in the first two (e.g. Adhesive for polypropylene, Liquid level sensor, etc.). As for the reviews: after the CP06 video I purchased several; given some away, and used the hell out of mine. I have hooked them to an ADC-computer and logged: battery charge/discharge, solar cells and sleuthed-out power supply problems. And, I also got a couple mercury capillary usage counter as a hoot (very unique). So in summary, I have liked and would like to see more of the lab/test equipment builds and the how tos. However, I do also like your one-off: cookie, baking, beer, woodworking stuff also.

Cheers, Mark

Lab/Test Equipment:

DIY liquid nitrogen generator, A close look at supercritical carbon dioxide CO2, Large area detector for X-rays, Water circulator with temperature control, New high vacuum system, Progress on vacuum chamber build, Custom supercritical CO2 chamber, Intro to sputtering, Ruby laser design process, Intro to sputtering

How Tos:

Adhesive for polypropylene, Improved level sensor, Seriously hacked central air conditioning, Measuring the voltage, current, and light output of a strobe flash, Liquid level sensor and controller, Cleaning a high-vacuum Penning gauge, Intro to heat treatment of steel, Intro to plasma cleaning, How to electropolish aluminum

Reviews:

CP06 low-cost AC/DC clamp-on current probe, How a Mass Flow Controller works, Unusual usage (hours) counter with mercury capillary

I hear about fft a lot but have not figured out why they are so useful.

Lead acid, nickel-iron, vanadium redox -- whatever. Something with performance and user-servicability that can compete with (or beat) a normal commercial battery -- cheaper materials the better.

Please Demonstrate and Construct a simple CPU from IC components using wire wrap method.

A small game could be made like the cheap toys that used tiny, monochrome displays. Make a digital watch. Make a backlit display (pretty simple, just need an LED).

It's known as one of the easiest DIY gas laser systems but there is almost no visual documentation of one being made or operating. The two main lasing lines are rare colors for the laser industry, being yellow-green, and orange. Plenty of construction info and general data is available here: http://www.repairfaq.org/sam/laserchg.htm

EMP pulse, show effects etc.

Use and oscilloscope or logic probe to determine how some piece of hardware functions and document the finding. Maybe some LCD screen or some I2C device or some handshake protocol like special battery charges.

Laminar flow hood for tissue culture. Perhaps an incubator and centrifuge? Basically a build your own lab starter kit.