9 volt battery supply. Load is 12 ma. I figure a pass transistor operated by the switch and/or circuitry will be fine.
Ideally the switching circuitry is on the load side of the pass transistor, hence no quiescent draw. That may not be possible. If it must draw quiescent current then I will have to assess the feasibility of it. Two switches is not the end of the world, just not as elegant.
Is there any reason why you can't use a straightforward single pole toggle switch? It is cheap, ergonomic to operate, draws no quiescent current when open, gives negligible volt-drop when closed - and is self-indicating.
If they had only just been invented, they would be regarded as one of the biggest steps forward in technology of the past 30 years.
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~ Adrian Tuddenham ~
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But many customers just push on and leave on battery devices. On second thought, I am going to randomly disable the auto-off feature. I am starting a batteries on-line business.
And if you need to switch more current than the lamp switch can handle, use it to operate a power relay. BTW, if you go the 7474 route, be sure to debounce the switch.
The comparator is self-latching, after power-on output is high (for minimum current drawn). Alternative: connect the 10n to +, then it starts with output low.
Pressing the switch less than 1 sec switches the state. Repeating the switch presses fast does not switch state (slow debounce).
On a sunny day (Wed, 13 Feb 2008 23:13:22 +0100) it happened "Arie" wrote in :
I must say I am impressed, a nice solution. As to the issue what is 'nest', this uses 10 components, 2 of which are capacitors.
Placing, board size, vias.... I did say 74HC74, but even that requires some debounce, as others have pointed out, so at least 2 more components.
The OP says he has no micro. But how a about a simple 8 pin PIC? Use the internal osc, internal pullup at an input pin, trigger interrupt, flip output, hang some milliseconds in interrupt routine as debounce.....
It is all there, with *1* component, say a PIC 12F629, only 67 cent in volume.
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And, it also has a build in comparator that perhaps can replace some part of the rest of the circuit.....
I would definitely go that way, have been using that PIC to replace simple circuits no several times. That way you need to have only 1 part in store.
Actually, that is not that bad, because you use the other half of the HC74 package to debounce. However, to do it right you need a SPDT switch: no capacitors needed.
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