I work at a store that buys returns from stores such as harbor freight, home depot, amazon, costco, cvs, etc. I've stripped down a number of electronics that weren't worth repairing. Power inverters have a great number of useful parts in them, the bigger the better. Stereos, microwaves, ipod docks, I've even salvaged a few useful parts from a portable heart rate monitor.
I like to take old circuit boards of all types and scavenge all the parts I can. I get motherboards and desolder the coin cell holder, and some jumper posts for use on the ends of breadboard jumper wires.
Not exactly super-duper but if you give it a long and hard look most of the technologies we are using today has been given some engineering time. For example, if I was to design a 1KW portable system based on nothing but today's technology I do not scale down - I scale up. It is easy to see. Capacitors scale up, so are ICs to handle them, and the next time you care to pay attention to X5R 0804's at 220 uF 6.3V are at the cost of some USD 0.00000001 - and the technology to make them or stack them increased so rapidly that THIS would make sense.
Granted, we are in the future here, but the ones without a ready design for it loose out.
About 5 years ago my garage door opener failed after a nearby lightning strike. The control board was toast, but I was able to tap into the receiver portion and add a few ice cube relays to get it working. Still working great.
I did the same thing with my 1970's era vintage arcade pinball machine. When the old cloth-wrapped relays burn-out, I use the ice cubes and they work great. (Plus, I have sockets on those for future easy replacement).
A really good source of "interesting" parts is the typical "hamfest" that includes parking lot flea market activity. Hamfests are really popular here in the States, but I imagine similar activities occur elsewhere. Hamfests are held all year long at various locations around the U.S.A., but most of the activity occurs during the spring and summer seasons. The "fine junque" on display is usually (but not always!) centered on used amateur radio gear and obsolete test equipment. Most hams try to unload stuff that has been wasting space in their garage or basement, and many are willing to bargain heavily to avoid having to cart the stuff back home. Know in advance from some Ebay shopping what the typical selling price is, be prepared to pay cash (no checks or debit cards or credit cards), and be prepared to haggle. If the price isn't "right" come back near the end of the hamfest to see if it is still available and at a lower than "asking" price. Don't be afraid to walk away empty handed.
Another good source is surplus electronics dealers, which can be found on the Internet. Plan to visit in person if possible. We are blessed here in Dayton, Ohio USA with Mendelson's Electronics with football-field sized aisles of the most amazing things, all more or less assorted by function. Bring a VOM, preferably something that also reads capacitance and inductance if you have such a gadget. There were several new LCR digital VOMs for sale at the recent Dayton Hamvention® but I managed to resist the temptation to throw down almost $200 for the Hong Kong import.
I got a great big stack of linear Pot's from a 20 Chanel graphic eq that was in a bin. Also a bunch of filters pre arranged and waiting to be re-located.
Plasma Tv's have a mother load of HV and power silicon. As well as good frame steel.
I have a 3d printer/cnc frame I welded from Plasma TV frame.
Giant solar death rays can be had from rear projection tv's (both LCD and CRT) it you peel the screen apart there is a giant magnifying lens. You can focus nearly 2sq meters of sunlight down to a square inch. Big ones can melt/vaporise almost anything. (wear welding gear if you try this, the reflected light has heaps of uv, causes sunburn and eye damage similar to welding. NEVER LEAVE A LENS IN THE SUN UNATENDED!!!)
Printers, especially big commercial ones and photocopiers are great for metal for welding, as well as motors and optical/hall sensors. High Grade steel and stainless rods are great for reinforcing welding projects. My sand scoop I use metal detecting has printer parts in it.
I just fixed my bench grinder with microwave caps.
I have an Ion thruster on youtube I made from an old crt flyback, salvaged heatsink, old speaker wire and a salvadged resistor with a 2n3055 (the only purchased part) as a high voltage joule theif for the 40kv supply. The flyback lives in an ice cream tub filled with vegtable oil. The thruster itself is made from a coconut cream can (from a Satay that was delicious) and a paper clip.
Getting ready for a Chinese invasion from the South China Sea?
Instead of making islands, they may just try to take yours.
Protect the homeland (and don't kill yourself with your projects in the process)
since you mentioned optical mice, I recall one laser mouse having such a sensitive detector to bring it out of sleep mode that when I inverted it, I found it detected a finger motion on the center axis 2 meters away.
I think It does this by using a fresnel lens and interference patterns.
Then again back in late '70's I was tuning the length of a dipole with a directional coupler to measure reflected power and thought I had invented a motion detector anywhere in the big lab with a matched antenna -30dB, it was very sensitive to being detuned by reflections. Naturally my naive thinking, it had already been done before.
My son once took me to see an online friend of his in Ohio who had a garage full of surplus equipment from White Sands military base.
He was the guy who demonstrated 80mpg on popular science long ago running off water. He used exhaust superheated steam injected into a carburetor in an old F-150. It was also mixed with gasoline. to get started. He had since updated it with PIC controller and still drives it. The main advantage was a high vortex velocity device inserted in the manifold with curved blades to improve air-water-gas mix.
He has a gold plated wire rope in a loop and measured the resonant frequency, which he said changed with the lunar cycle.
This was around 2002 and he had a mass spectrometer for chemistry and lots of anthrax suits for chemicals due to anthrax scare and his phobias, but he invented some high energy glass plasma tubes to purify water for the military. He made his own PCB's and cover plates using a PC driven mini 3axis mill.
The biggest surprise was a high energy flame he made using 1/2" tubing and low pressure propane mixed with high pressure air injected in a right angle tubing to create a vortex. The pressurized air was preheated with a coil around the burner , so it looked like a propane torch with an RF tubing coil around it but after few minutes it produce a white flame that could heat up 1/2" iron rod tips white hot in seconds. He was hoping to invent a highly efficient LPG furnace, but it made so much noise , it sounded like a rocket.
He also made hand held glass inert gas tubes for healing using pulsed High voltage HF in the licence free band and sold hundreds of them to alternative healers and said he cured his cat of cancer with it.... It caused a slight tingling sensation with very little glow.
He was just a tech from Honeywell but dabbled in electronics all his life.
I was amazed by his shop and I used to have a similar lab at work in aerospace during the 70's.
I once did a similar "experiment" by accident while fooling around with my ancient natural gas-fired gravity furnace. Managed to ignite the gas in the air-mixing manifold instead of in the burner. The roar was quite satisfying! But I quickly shut off the gas feed and was afraid to try to duplicate the results. The problem I was trying to solve was a faulty bi-metallic switch that was heated by the pilot flame. When the thermostat on a kitchen wall called for the solenoid-operated gas valve to open flow to the main burner, the bi-metallic switch had to also be closed to complete the circuit. Finally got it repaired and haven't had any desire to duplicate the "jet engine" effect again... at least not on my home heating system!
There are lots of interesting things still going on in Ohio. And in Arizona. And New Mexico. Maybe Florida, too, but I haven't been there yet to find out. Not your usual suspects though. My favorite was the guy who used to do remote viewing for a three-letter agency. He was here in Dayton a few years ago. Don't know where he is now, but I sure would like to talk with him... this sort of thing is not appropriate for discussion in this forum because AFAIK he did it all without electronics... just his mind and pencil and paper. Paid well during the Cold War, or so I have heard.
I kind of doubt the remote viewing stopped. What I've heard is that they 'viewed' something particularly catastrophic, and it's been taken out of the public domain. Something about a solar flare that's supposed to wipe-out communications, and a lot of humanity. Not exactly 'Frankenstein's Components, but pretty 'Frankenstein' as nut-case theory predictions go.
The best nutcase in in West coast of Canada , often on Art Bell's old show said he made anti-gravitation machine. The Japanese interested parties came and left. No such repeat demonstration. Possibly a magnetic levitation of a metal object inside a bowling ball or recreational pharmaceuticals.
Scammers, perhaps, but there is a vast number of people in the world that fervently believe mutually incompatible things on the basis of almost nothing.
As a species we're very good at spotting patterns (even ones that don't exist), because the penalty for failure to spot the real ones used to be death.
Lots of people have lucky underwear, ritualised methods of gambling, and other far stranger beliefs.
It can be a fun game to spot them in yourself. Have you ever found that something wouldn't fit, so you went and measured it again? Or picked a raffle ticket because it was the first in a book, or the last, or was your favorite number? Why did you do that?
Confirmation bias is one thing that can make you do weird things because you remember your successes but not your failures, and you can be very optimistic about seeing a near miss as being a success rather than a failure (see also "cold reading")