"Simple" hour/minute binary clock?

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

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

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

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

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.

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.