"Simple" hour/minute binary clock?

Yes, that would work better. I don't know what the chips needed to run this are rated at (I'm waiting to see the schematic from John so I know what parts I need to get at Radioshack - we've only got one in my area that stills ICs and not just cell phones, and it's a long drive so I only want to make one trip). Once I know what I need to pick up I guess I'll have to figure out what they run at. Like I said, my knowledge of circuits, etc. is limited to following schematic diagrams I find online, but in my experience, everything I've used has run on either a +5v or a +12v. In the past I've had to get creative with batteries, hooking a few of a certain type in parallel and then hooking the parallel "bunches" in series to get near the right voltage - very inefficient and costly, but it worked and the batteries lasted a fairly decent length of time. My other option, which I don't want to do here, is stripping the ends of a cheap A/C adaptor.

I picked up a few books the other day on beginner projects in electronics, hoping to find something in them like what I've requested here, but no such luck. They've taught me a lot, though, and I'm already thinking of ways to adapt John's circuit to drive something other than LEDs (but I'm going to tackle getting this to work, first). Thanks again for all your help and once I have schematics and a finished product, I'll be sure to post a link to a picture.

Buy a set of clip leads and you can connect to the adaptor. Rat Shack should have these.

is a place to shop if you can make up an order. Check out their kits also.

A wall wart is perfectly acceptable, and will get you your +5 without you having to design a power supply.

I've seen switching wall warts smaller than a pack of cigarettes, with

5 to 10 watts out - you could hide one of those inside your enclosure.

Good Luck! Rich

I wouldn't use NiMH's for anything. I've had a very bad experience with a couple of batches of NiMH's that after about a year's time, wouldn't even hold a charge.

If you can get low enough current with LED's, I'd suggest 3 or 4 C or D alkalines, and use CMOS, which has a wide supply range.

But, like I said a couple of posts ago, a wall wart should be perfectly acceptable.

Good Luck! Rich

I'll admit that some of the really cheap ones I've gotten aren't all that great, so usually they end up in the kids toys. ;-) For "good" NiMH batteries, I've usually paid around $10 for four (Energizer, Panasonic, Rayovac, etc). I've not had any of these go bad yet.

Jeff

--
    "They that can give up essential liberty to obtain a
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Rich Grise wrote in news: snipped-for-privacy@example.net:

A lot of NiMH troubles can be traced to microthicknesses of grime or nonconductive salts on the terminals. I had some that looked like they were decaying at different rates in charge retention, and I decided to try a bit of brasso on their terminals and give them another go, and they behaved equally again, camera use went from around an hour to around four hours. That's a big recovery considering there didn't appear to be a problem with terminals before cleaning. It doesn't take a lot for the charger to fail to push enough current, it can drop well before the little LED's make the failure obvious.

Re alkalines, are any of them rechargeable? That's not a facetious question, if there are any, I want some.

Fascinating - thanks for the report.

Some Caig Labs DeOxIt might be equally effective at getting off the grime and restoring the contact quality.

Rayovac used to make specialized rechargeable alkaline batteries. I gather that these are discontinued (they never really caught on) but that Pure Energy in Canada is making equivalents.

They do work, I understand, but aren't an ideal solution. They apparently start out with a charge capacity similar to a standard alkaline, but their capacity drops off somewhat each time they're discharged and recharged. There seems to be an inverse relationship between lifetime (in number of cycles) and depth of discharge - deep discharge reduces the number of total cycles you can get before the battery is degraded to the point where it's no longer useful. Also, a specialized charger is required - a standard NiCd or NiMH charger cannot be used.

Although Pure Energy states that their battery can be recharged up to

500 times, another report I've read suggests that 50 cycles at half-discharge and 10 cycles at deep discharge can be expected, and that a complete discharge can leave the cell in a non-rechargeable state and thus kill it completely. Possibly the technology has improved since the latter report was written in 2002, or possibly the 500-cycle number assumes a very shallow discharge.

Rechargeable alkalines also seem to have a relatively high internal resistance, which limits their ability to deliver high amounts of current (400 mA max for an AA cell is suggested by one writeup).

For most rechargeable applications, NiMH seems the best solution for devices that you can keep "topped up" on a charger frequently, while the older NiCd types may still be best for applications where you need to charge the device and then stick it in a box and not think about it for several months and then expect it to work reliably.

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Dave Platt                                    AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
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I just posted the schematic and some supplementary material to abse
and also emailed it to you since you can\'t access abse through
Google groups.

A project? A CD4040 binary counter chip, some sort of clock oscillator (a 555 would do for testing purposes) & a bunch of LEDs would do the trick nicely.

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 . | ,. w ,   "Some people are alive only because
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Nope.