Re: gEDA-user: SMD soldering challenge status

[Mike Jarabek <mjarabek@xxxxxxxxx>]

Hi,

On Sat, 2006-08-05 at 14:56 -0400, DJ Delorie wrote:
> > The success of this circuit depends on what `low' valued means here.  To
> > get visual frequencies, for a couple of Hertz we might need between 0.1
> > and 1 microfarad or so.  We would have to breadboard the circuit to find
> > out appropriate values for the cross coupling capacitors.  (Although
> > probably not with those 01005 components... ;-)
> 
> The least expensive ones are in the pF range.  We can afford one or
> two bigger ones, but we can't afford to make them all bigger.  Plus,
> you'll need a resistor or two, those are more also.
> 
> If we did multiple transistors, they'd have to be different sizes (not
> a big deal) and you don't get the fine-pitch challenge with them, like
> you do with the mini-gates (SOT-323-5 and TVSOP).

We could make an RC oscillator with the inverter, the kind that charges
and discharges a capacitor from Vil to Vih and back again.  We would
need at least one inverter with hysteresis. The output of the first
inverter would be driving an LED. Then another inverter could drive
another led.  Then the resistors could have larger values and the
capacitors smaller values if the inverters are CMOS.

Does a Schmidt input inverter cost too much?

-- 
--------------------------------------------------
                              Mike Jarabek        
                                FPGA/ASIC Designer
  http://www.istop.com/~mjarabek                    
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