Thinking about the OpAmp solution, wouldn't a comparator be even better/more
suited to my application?

LM339 quad would do the trick, (or rather a pair of them - I need 5
comparators - bugger!)

I assume the LM339 can switch at 1kHz comfortably?

You mention a decoupling capacitor on the supply.  I am using an LM317LZ vreg
to provide regulated 5v, from a 12v DC input (& another for 1.5v) for PIC and
possibly now the LM339, which has a 0.1uF(IIRC) capacitor on the output
already - so will I still need a further decoupling capacitor for the IC?

Regards,
Mark

> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu]On Behalf
> Of Russell McMahon
> Sent: 02 December 2004 23:37
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE]Darlingon array, was Will this voltage 
> shifter work for
> m y application?
> 
> 
> > Is this what you were suggesting?
> >            +5v
> >            /
> >            \ RL
> >            /
> >            |------>Vout
> >           |/
> > +1.5v -->--|   Q1=NPN
> >           |\
> >            |
> >            |<-------Vin
> >            \
> >            / Re
> >            \
> >            |
> >           ___
> 
> Not quite.
> Remove Re (open circuit) and add a series resistor between 
> +1.5V and base. 
> (Probably about 10K depending on currents involved. Coild be 
> 100k if signal 
> levels only. The transistor is not "aware" that the input is to its 
> emitter - it simply turns on when Vbe is large enough and off 
> when its not.
> 
> > What affect on my FE33 1.5v module will Vin have when Vin=0v?
> 
> About none when built as above.
> 
> > Will Vout actually make it to 5v?
> 
> Definitely. Make Rl high if a PIC is the only load - say 
> 100k. The resistor 
> between +1.5 and base couild also be 100k then (even 1 M but 
> 100k is fine). 
> The current sinked (sunk) by the Vin cct will be about 5v/Rl + 
> (1.5-0.6)/Rbase.
> 
> > Is this ok to drive in to a PIC?
> 
> Definitely.
> 
> > Am I right in saying that a darlington pair is non-inveting.
> 
> No. A darlington pair "looks" like a high current gain 
> transistor with a 
> double normal Vbe drop and poor Vce saturation. Draw one out 
> and mentally 
> apply currents into the base so that the first transistor 
> tuirns on. Work 
> out what happens from there.
> 
> > for some reason, I have a mental block with regards to 
> using op-amps, I 
> > don't
> > know why.  It is a simple practical solution to my problem, 
> so I really 
> > should
> > pay it more attention.
> 
> You should! When used in circuits like this one an opamp is 
> extremely simple 
> to understand - much easier than a transistor. You can do 
> many useful things 
> with opamps with a reasonably minimal level of understanding. Just 
> understanding their operation as a black box differential 
> gain block is all 
> that's needed to get going. NOT conceptually or practically 
> hard. There are 
> many tutorials on web. Have a look.
> Googles ....   "op amp tutorial"  200+ hits.
> Surprisingly, most seem to wade in to the middle. There will 
> be a "black 
> box" explanation if you look for it.
> 
> > I need to convert 5 signals, one of which is (IIRC) a 1kHz 
> data clock 
> > which
> > clocks in small 13-bit data bursts every 10 seconds.
> 
> Probably 5 transistors and 10 resistors is an OK choice if 
> you don't want 
> inverting.
> 2 x LM324 opamps plus 2 resistors would be even better :-)
> See my pinout description in an earlier post. This is the 
> complete circuit! 
> (Add a power supply decoupling cap). Just connect the 
> reference to the same 
> 4 pins on the second opamp. Output swing should be high 
> enough for a PIC 
> input but i haven't checked that. Adding a pullup per channel 
> would help but 
> adds components.
> 
> 
> 
>         RM
> 
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