Well, yes, but for that pumping to happen the PIC must be operational
and well past its POR/BOR boot process.
John said:I've said, three or four times now, that the cap voltage gets boosted
at turnon, all by itself, because that's the way Ls and Cs behave.
Given a reasonable C value, there should be plenty of energy available
for the pic to start up, and begin pulsing the npn, before the voltage
on the C discharges too much.
+1.5V----switch-------1mH-----|>|-----+--------->
diode |
|
|
1uF
|
|
|
|
gnd
Simulate it!
But, as Jim would put it, how does it start?
John Larkin wrote:
Ok, ok, I did understand. Works like the kick starter on older Harleys.
Either the engine jumps to life, or it doesn't, or it lets off a loud
bang and clears the exhaust, or you fly over the handle bar and the
ankle hurts like heck.
Here's hoping that it's enough time to start everything. 1uF ain't a
lotta microfarads ;-)
Martin said:The challenge here is to do it cheap, compact, with easily available
bits and a low parts count in a form that will work reliably for a
home constructor. There are quite a few hobby PIC circuits that would
benefit from a single 1.5v battery.
Frank said:What's wrong with the MAX1724? It is not cheap, but has all other
attributes you listed and starts from as low as 0.91V
Clifford said:There is an MOQ on the MAX1724, like one reel (5000), but
the Iq of 1.5uA is unbeatable.
The challenge here is to do it cheap, compact, with easily available
bits and a low parts count in a form that will work reliably for a
home constructor. There are quite a few hobby PIC circuits that would
benefit from a single 1.5v battery.
Martin said:This solution has an admirable minimalism and might be a winner too.
OTOH it might suffer from occassionally killing rather than curing.
Worth playing around with though and smaller than the more easily
explained dpdt switch and series/parallel capacitor.
OTOH at 10-20uA off 3v it is a load equivalent to 200k so with 1uF
gives a tau ~200mS.
I'd expect a PIC to be fully operational driving outputs well before
then - even on slow minimal energy 32kHz clock.
Frank said:What's wrong with the MAX1724? It is not cheap, but has all other
attributes you listed and starts from as low as 0.91V
Martin said:Tricky bit is getting the PIC to start from 1.2-1.5v in the first
place.
I wasn't sure that this would work since it looks suspiciously like a
perpetual motion machine. I think it has to transfer energy from the
battery into the series capacitor if it is to be sustainable.
I did wonder about the idea of making the on-off switch a dpdt with a
low leakage capacitor across the battery when the unit is switched
off, and in series when switched on. And then a boost converter to
keep it topped up during use. The PIC will start at >2v and keep
running once started a little lower than that.
There are clock outputs at 32kHZ(unbuffered), and buffered 8192Hz and
~50Hz available
I think I like the Joergs idea of the 74AUP1G14 low power Schmidt
trigger inverter best. Cheap and probably cheerful. There is something
appealing about getting low current stuff to run off a single 1.5v
cell efficiently.
The challenge here is to do it cheap, compact, with easily available
bits and a low parts count in a form that will work reliably for a
home constructor. There are quite a few hobby PIC circuits that would
benefit from a single 1.5v battery.
