|Re: Anyone know what became of the NEWT project?|
Message #21 Posted by don wallace on 1 Sept 2005, 7:35 a.m.,
in response to message #20 by Garth Wilson
Well, Garth is right on with his tips for soldering smt.
I scrounge smt parts from old motherboards and have done
quite a bit of smt board component level repair...
On the level shifting question, yeah thats tricky but I think
enhancement mode fets might be the best bet if you can get parts
with the right on gate threshold? failing that yeah your standard depletion mde fets driven with inverted signals is the best bet
I imagine Monte.
The 339 is a really nice comparator. But they do draw about
200 uA per comp I think. I wonder if there is a real low power
or programmable ( adjustable chip Iset) quad or octal part out there somewhere?
Maybe a very low power cmos opamp with hysteresis would be
fast enough and have programmable Iset (I am thinking of some very old Intersil cmos linear parts but could bet they are gonna be way too slow. Maybe there is something more modern in the same vein?)
I have not thought this through at all but maybe you might
even be able to use a BIPOLAR transistor in common base mode.
I can't draw the ascii art in this form...
But you set the base at a threshold plus (about) 0.6 volts.
You pull down via a low value resistor on the emitter (of npn device) and the collector follows it down, but level shifted. Effectively open collector output ;-) Plus the collector comes right down to within the saturation voltage of where the emitter
is dragged... Current gain is about 1.00 ;-)
Probably would not work for many of the signals but maybe worth thinking laterally like that anyway. Fast too. Maybe for one or
two signals you can just shed volts by using a diode or two? IR led? Just a thought... Low parts count anyway.