A NE-2 bulb ,
resistor and cap is simpler and test-able* assuming
you have the power supply free already.
I like it, even thoguh I did say
'LED' :-)
So, put a LED in series with the NE-2. :-) (Hmm, been too long - is
the NE-2 on-state current high enough to light a LED?)
I was trying to design something analogous with a LED...maybe a zener
and a SCR could be combined for similar effect?
V+ ---- /\/\/\/ ----+---+------------+
| | - |
| | | /| |
| | | +---|< |--. ---
+-----| |------+ | \| \ V
| | | - -------
| ___ |
| / \ |
| +--- /\/\/\/ -----|-|<|-|---+
| | \___/
V- --+---+
Provided the two resistors combined keep the steady-state current below
the SCR's dropout current, that ought to work. Add three transistors
so that current through the LED shuts off V+ to the charging circuit
and it should work even without that. Showing the transistors as boxes
because of the limitations of text graphics, and using an NPN as the
inverter:
---------
V+ --+----+--------| E C |---- /\/\/\/ --+
| | | PNP | |
| | | B | |
| | --------- +-------+
| | | | | | |
| +-- /\/\/\/ --+ _____| +-------| |---------+
| | | ^ | | | |
| | /_\ | |
| +--- /\/\/\/ --+ Zener | | |
| | +----. --- SCR |
| | \ V |
| | ------- LED |
| | | ___ |
+---|-------- /\/\/\/ ----------+ | / \ |
| | +---(-|>|-)-----+ |
--------- | \___/ | |
| C | | | |
| NPN B |-----+-- /\/\/\/ --+ | |
| E | | | | |
--------- | | | |
| | --------- | |
+-- /\/\/\/ --+ | C | | |
| | NPN | | |
V- ------+------------------+---| E B |---+--- /\/\/\/ --+ |
| --------- | |
+---- /\/\/\/ ----+ |
+------------------------------------+
The only way I can see that failing is if the amplification of the
switching transistors is so low that SCR holding current isn't enough
to end up switching off the PNP.
By this point, though, you might as well use the two-Q two-C four-R
astable circuit, possibly with another Q as a switch for the LED. The
major advantage of this is that the charge accumulated in the charging
capacitor is the power used to light the LED - though you need to use
FETs instead of BJTs for the switching for that. But build the astable
with high Rs, low Cs, and FETs instead of BJTs, and you have very low
parasitic power draw there too.
Oh well, it was an interesting gedanken circuit. :)
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