Simple useful circuits

I'd suggest solar charging controllers for 12V lead-acid batteries and also a low-voltage cutoff to prevent deep discharge of 12V lead-acid batteries. Smaller versions of the same things but for a single lithium ion cell (maybe charge to about 3.9V, cutoff load at 3.0V) might be useful too. If you get fancy, a maximum power point tracker in the charge controller could possibly be worthwhile.

Whilst not useful to most people, I use this a lot:

I doubt that obtaining and programming the microcontroller from just scrap electronics would be feasible, though I did get one of those displays out of a discarded fax machine. Having this device makes it much more practical to then re-use capacitors and inductors salvaged from scrap, for building other things. With different software and a little more hardware, you could make additional use of the same processor and display and add functions for frequency counter, ESR meter, crude voltmeter, thermometer, etc.

An adjustable regulated power supply might be useful.

Also, a time switch to turn off a light after a delay (maybe a LED lamp or a relay driving a mains lamp), to prevent it using excessive amounts of energy if someone forgets to turn it off.

An efficient dimmer for running LED lights from a battery might also be useful for prolonging battery life.

Perhaps a 12Vdc to 120Vac or 240Vac inverter could be made using the transformer of a PC power supply backwards along with some high voltage transistors from CRT monitors (e.g. the MOSFETs used in re-tuning the flyback depending on the horizontal frequency), though I am not sure how useful this would really be.

An electric fence energiser might be useful in some areas. If you came up with a design that produces an output that conforms to appropriate standards such that it won't kill anyone, that might be a good thing.

Maybe a triac speed controller for universal motors in power tools would be useful in some places where they have mains power.

Also for people who have mains power, a temperature controller might be useful, if it can be more reliable or give better control than a mechanical thermostat.

This guy is trying to build open-source medical equipment:

I've only spent brief periods in the 3rd world (brief as poss, actually) but the most useful thing to have there IMV would be a taser. They can be easily rigged up from junk parts, too.

ic junk. What simple circuits have you found useful? Whether as tools or en d products. Have already done minimal versions of audio amp, sig gen, alarm , voltmeters. I've a list of ideas but I'll bet you have some interesting o nes I've not thought of.

RC + buffer + relay or tr might do that. How would you work out when someon e wanted the light to stay on? A push switch is crude, but would work for s ome situations.

I'd also like a cheap version of a PIR, but haven't figured out how. An LDR can sense light level changes as people pass by, but only works very short range - and is no use after dark. A LED could probably replace the LDR.

Simple switch mode current reg maybe. One issue there is working with a wid e range of unknown cores - plus of course unknown transistors. Maybe one wo uld need to design it to slide gracefully into linear mode when L didn't cu t it.

I did once build an SMPSU using wire wrapped round a steel screw, but don't know if that could somehow be worked to keep the losses down. Perhaps it c ould work sm when able, and linear when not. SMPSUs aren't my speciality.

With an invertor I'm quite tempted initially by a simple buzzing relay. Cru de, but that way a lot more folk could build them. Then could add something like you describe, more sophisticated.

There are a few things like that that would be useful, but I just know they 'd end up being used for all sorts of horrible mischief.

or just cheaper. That's usually the barrier. At some point I'm hoping to cr eate bimetal thermometers, thermostats & ammeters too.

Well, a good list of ideas to chew on, thank you!

NT

I think you want to start with real, absolute basics. Going from the electrification of the US, the first two would probably be lighting and radio receivers.

If you assume that the available radio traffic is AM below about 10MHz, then a simple regenerative circuit (or even a crystal radio) would do wonders. As available as LED flashlights are these days, possibly the best way to provide more permanent lighting solutions would be to assume that people can get them, and provide simple buck regulators from 12V lead-acid batteries down to 1.5 or 3V, along with instructions on how to hack a flashlight designed for dry cells to work off of the regulator.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com

Yup.

I love the result per cost of reaction sets, but the inevitability of lots of howling transmitting sets rules them out. I've racked my brain for a way to make them oscillationproof, but it seems there really isn't one. If peo ple read about and understand reaction, they will inevitably mod the circui ts to get more sensitivity, and a big problem would have been unleashed. An other approach is mutiple stages for isolation, but then it loses its simpl icity and cost advantage.

Crystal radios are a must. I'm thinking of bringing in someone with a lot m ore experience on them than myself. Carbon amplifiers might or might not al so be worth a look.

LEDs I shall tackle, simple resistor ballasts then something smarter.

I also want to do a ballast that will run dead CFLs, which are much more av ailable.

NT

And please include a discharge protection in the circuit so the battery won't be further discharged than 10.5 V. People have a tendency to keep the light on until absolutely nothing comes out anymore. Fat chance the lead-acid battery will be gone after a few cycles like that.

10.5 V is the lower limit until where you can go at light load for a 12 V LA battery.

joe

Although your heart's probably in the right place, you'd be better off concentrating on simple circuits period, until you become more familiar with the needs of an adopted client.

There's a lot more repair savvy in places where it still pays to do so. Perhaps more than you realise.

A good educational or hobby circuit is good anywhere. Anything that cuts down on battery costs, keeps a light on after dark or the com lines open has about as much use as electronics can have, anywhere.

Definitions of junk differ from neighbourhood to neighbourhood, city to city - never mind country to country and continent to continent.

RL

From experience I have found that the circuit for a CFL still works after the fluorescent tube has gone bad or become broken. I used one to replace the electronic ballast of a 10W circline lamp. The components might be replaced with higher power, or paralleled, to drive larger fluorescent lamps more efficiently than the old-fashioned inductive ballasts.

Also, the LED lamps I had, that failed, were the result of overdriven or defective LEDs, so the circuit could be re-used for other LEDs, or other applications where a constant current supply is needed. The 9W LED lamps I have use two strings of nine LEDs each so the circuit puts out about 30 VDC at 300 mA.

These circuits work on both AC and DC, and as low as 40-50 volts, so they could be used on battery packs or phone lines.

Discarded portable power tools may have good motors and variable speed drives that could be used for small vehicles such as skateboards or bikes.

"Joule thief" circuits can be used to extract energy from mostly exhausted batteries, or from photocells or small low-voltage generators powered by wind or water.

Good luck with your project.

Paul

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Yup, a project on CFL repair was one of the first things done. So far thoug h I've yet to find another use for the ballasts. They don't have the necess ary isolation, and few have enough space to add another winding, let alone any kind of insulation barrier beyond the enamel.

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I think its easier to just put near-flat cells in series, they're available in most places aplenty. An smpsu that runs on a whole bank of cell pairs t o provide more useful amounts of power out would also be some use.

Microgeneration is something I'd like to do, enough power to run an LED or a few could be very useful. I've looked a bit at things like gravity genera tors, syringe based engines, thermopiles, hand cranked chargers etc. One of the problems is making gearing, I've yet to come up with a practical way t o do so. Hand cutting gears from printed templates is excessively slow, and the result limited.

NT

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ugh I've yet to find another use for the ballasts. They don't have the nece ssary isolation, and few have enough space to add another winding, let alon e any kind of insulation barrier beyond the enamel.

Looks like this is solved. Feed the ballast output to a ferrite core salvag ed from a CFL ballast, on which are 2x low v windings, separated on the cor e.

r a few could be very useful. I've looked a bit at things like gravity gene rators, syringe based engines, thermopiles, hand cranked chargers etc. One of the problems is making gearing, I've yet to come up with a practical way to do so. Hand cutting gears from printed templates is excessively slow, a nd the result limited.

A partial solution seems to have been found there too. Cut discs from wood/ plastic, spin/sand/crown and use with rubber bands. Toy power levels only, but that's enough to light

[snip]

You might be able to use an endless chain and a sprocket, as found in cuckoo clocks. The chain would ride on a small sprocket and you can just remove weights at the bottom and clip them on the top as needed. The axle of the sprocket could be connected to a fairly heavy flywheel that would store momentum while the weights are repositioned, and the outer surface of the flywheel can connect to a small pulley on a DC motor acting as a generator, using a rubber band or large, thin, flexible O-ring. I used that for my wobbler air engine:

Paul

How high is high, and what ratio do you need? Can you scavenge chains and sprockets from a bicycle, maybe with two or three intermediate jackshafts to get the overall ratio you need?

----- Regards, Carl Ijames

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When I looked at it before I was looking at 0.1W output for 30 minutes per

6foot 20kg fall, IIRC. So the sped of descent is imperceptibly slow. To get what you suggest working would take a flywheel the size of a house. Howeve r... I can see no other way to reduce the torque to work with the relativel y weak mechanics one can readily made from junk. But a massive sheet of woo d or plastic would be prohibitively expensive. Round and round we go, with a problem no matter what way I look at it.

There is one other option, but I'm not loving it. Use more rapid descent to charge a NiMH cell. It costs, and dies after a while, especially consideri ng that charge rate would necessarily be very high, it would have to be to be practical.

But it seems to me the battery probably is the most cheap & practical optio n.

NT

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a few 10s of kilos hanging on the outside of the wheel

from impercetibly slow to at least 500rpm, so approximately infinity to 1.

100% efficiency would be nice too :)

to

It's possible, but would be way too expensive. Really that's what it would physically take to do it, it's just not affordable. I think in the end, unl ess one has access to proper bearings, metal fabrication etc, which these f olk definitely don't, then it's not really possible to make something that will do the job at an affordable price.

1 or 2 NiMH cells is the only workaround I can see that may actually work. It would allow reasonably sized bits of wood to provide a rapid descent wit h a brief extremely fast charge. 1 cell is cheaper, but would lose a lot of efficiency with diode & transistor V drops.

So the main question becomes: how do NiMH respond to this sort of aggressiv e charge regime? I'm guessing it's heat rather than current that can damage during charging, and chucking amps in briefly probably won't raise the tem p too much. Subject to testing.

NT

Looks like around 1000:1. There's just no way we can make that many gear wheels.

Little plastic gear wheels are buyable, for some at least, but not big things that will take 30kg.

NT

How about a pulser to revive sulphated lead-acid batteries?

Tell me more. I've read a lot about lead acid revival, but the whole subject seems to be hotly debated. I need to do things I know work. I do have a couple of sulphated SLAs to experiment on.

NT

I've never had a good enough reason to try it. If it's a valid approach, you can bet people in poor countries are already doing it.

This maybe worth a read:

That slow charge bit was what we did back in the '50s when I worked for a car dealer. Plenty of dead batteries from the used car lot. IIRC very few, if any, actually fully recovered. A few worked well enough to get the car sold. I've had limited success at taking the cells apart and cleaning the sludge out and adding fresh acid. If that sludge gets high enough it can act as a short across the cell, or so I'm told. If the plates are damaged you can forget it.

I've recharged dry cell batteries enough, by jumping them across my car battery, to finish what I was doing. Like dead camera or flash unit cells at Christmas dinner.

About a minute or so will do it. Make sure that don't get too hot while doing it. Now days I always carry spares.