Re: gEDA-user: SMD soldering challenge status

[Mike Jarabek <mjarabek@xxxxxxxxx>]

Hi,

	Perhaps a bit more low-tech, how about an astable multivibrator?  This
circuit needs 2 transistors, 6 (or 7) resistors, and two caps.  Add two
LED's and you have a blinker.  We used to build these out of leaded
components on a 1.5 x 1.5 inch piece of perfboard.  We had students who
were in grade 5 assemble these from loose components, and they all got
the circuit to work.  The circuit can be built in one layer if you allow
a single trace underneath one of the components.

On Sat, 2006-08-05 at 09:34 -0400, DJ Delorie wrote:
> >    Even just a little 555-based LED blinker or something would count as 
> > "functional" in this case, I think.
> 
> 0603 cap = 1 cent
> 0603 led = 7 cents
> 
> Even the venerable 555 is too expensive in the small sizes appropriate
> to this project (about $0.60).

SOT-23 transistors come in at $0.10CDN at DigiKey in single unit
quantities.

> 
> Now, if you can think of a circuit that uses a flip flop and some
> inverters, plus low-valued caps (even resistors cost 3x what caps
> cost), that might be feasible.

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... ;-)

> 
> (ok, so it's more than just a *soldering* challenge ;)

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