Simple useful appliance?

On Wednesday, February 7, 2018 at 8:04:02 AM UTC-5, snipped-for-privacy@gmail.com wrote :

ge from your usual design projects.

are small amplifiers & oscillators, those have been done. Heating items suc h as kettles are excluded as they won't be very useful in this situation. R eaction radios are out due to legal issues.

ailable to a percentage of users. The item must be makeable entirely from p arts from scrap, your digikey budget is zero. So no uncommon components.

of use.

Hmm I heard somewhere that your best bang for buck in the third world is mosquito netting, to reduce malaria. An electronic mosquito killer?

George H.

How about those AC outlet testers- a plug with indicators. I once made a DC polarity indicator for a guy, so he wouldn't blow his VHF radio moving it from boat to boat.

Yes - that's been done too though.

NT

Yes - that's been done too though.

NT ============================================

Did they include frequency so they could verify proper generator rpm?

What do you mean by a "reaction" radio?

Developing world? A fairly high percentage of people in Africa have cell phones or smartphones (to discourage POTS line copper theft): It's much the same in other parts of the developing world. Methinks one can safely assume that electricity is available in some form to charge these phones. Presumably, they also have all the gadgets needed to operate a cell phone, such as a charging station: (The stand and platform on the left is a cell phone charging station). While minimalist design is a worthy exercise, finding a problem worth solving is more difficult and methinks more interesting.

Or, a percentage of time. I'm told that power in the developing world is often intermittent and unreliable. I have that problem living in the forest, where the power wires are known to attract falling trees. Damage to electronics from voltage surges usually occurs when the power is restored, so I unplug or turn off (at the breaker panel) power to any sensitive devices. The problem is that in the middle of the night, there's no easy way for me to determine that the power had been restored. So, I built a "Power Restoration Wake Up Alarm" that makes loud buzzing noises when power comes back. This might be a bit too complicated for the proposed design project. Instead, I suggest inserting a small power diode (1N4002) into the wall outlet. When the power returns, the diode explodes, making enough noise to alert or wake the residents. It can't get much simpler than a single diode.

Simple, but idiotic. A single tiny explosion isn't going to do much.

When the power goes out connect an 18650, unprotected, Li-Ion battery into the wall outlet. When the power is restored the Li-Ion battery will explode and start a small fire which will then trigger the smoke alarm. The continuous alarm is more likely to be effective.

Over here, making such a statement would result in you being called a RACIST and being trending on Twitter all day.

How about an ac relay, normally open type, in the power line input to the gadget you want to protect, with the coil powered from the "on" contact side. Power drops out, relay disconnects from power line, power comes back but will not energize the relay until you manually reset it, by pushing the contactor down by hand. Use a stick to push it!

Capacitor, 2 resistors, and 2 LEDs in anti-parallel is an indicator of power.

I use a night light.

positive feedback on the rf circuit - good sensitity, goodish selectivity with minimal parts count. The downside is the risk of oscillation and unintended broadcast of this interference, so they're no go.

NT

Probably this:

"A reflex radio receiver, occasionally called a reflectional receiver, is a radio receiver design in which the same amplifier is used to amplify the high-frequency radio signal (RF) and low-frequency audio (sound) signal"

positive feedback on the rf circuit - good sensitity, goodish selectivity with minimal parts count. The downside is the risk of oscillation and unintended broadcast of this interference, so they're no go.

NT

I used exactly the same thing for a few years until I switched to the visual-plus-audible mains alarm that I posted here in another thread some time ago.

One could even dispense with the capacitor and use a single resistor. Not much current needed just for a visual indicator.

I like how you think... handheld population control. Heheheh...

Lead 'em down the path... to the next plane of existence.

The absolute best way is to have a nice say 22kW Generac backup generator AND a good power conditioner on your system.

Then, you simply go to sleep without a worry about what happens or happened to your power that night.

Put some of your lights, your heating and air system, your kitchen, and your computer UPSs on it. Your neighbors will always say "he's the only one on the street who's lights never go out.

Back in the early 1970s, I made several *non*-reflex, non-superhet radios with a single transistor RF stage and gave them away as novelty gifts. The RF stage was fixed tuned to the local AM station which conveniently broadcast at 540 kHz.

I used readily available 455 kHz IFTs after removing the capacitor - usually 200pF - and replacing it with 150pF to enable them to tune to 540 kHz. A Ge A079 diode served as the detector and I even included AGC.

For the RF stage, I used whatever RF transistor I had on hand - AF117, 2SA15 (PNPs) or BF195 (NPN).

I'm not clear what appliances would be protected from what

NT

Reflex and reaction are 2 different technologies. Sadly it seems the 2 refused to work well together.

NT

Coconut powered shortwave radio.