On Thu, 13 Sep 2007 01:11:32 GMT, "Bill" wrote:


"ian field" wrote in message
...

"John Fields" wrote in message
...

While seeming attractive at first blush, the down side of Ian's
scheme is that you'll need to build the whole thing using discretes,
you'll need a charging circuit for the battery, and you'll need to
replace the battery when it fails.


--
JF

The same basic configuration could be assembled with a CMOS quad 2 I/P
nand,
it might even be possible to retain the state with a supercapacitor.

I know what you mean by a cap retaining the charge but I never heard the
term super cap. What size and type cap would I need and how long would the
charge last? All ears, er, eyes..

---

http://www.google.com/search?hl=en&q=supercapacitor

The charge would last for:

(Vp - Vih) C
t = ---------------
I

Where t is the time in seconds,
Vp is the peak voltage the cap is charged to,
Vth is the logic's Vih(min),
C is the capacitance in farads, and
I is the current drawn by the circuit



--
JF