Viewing what is happening with an oscilloscope, which you may well
have done, is always very very very useful in cases such as this, (and
many others :-)).

Consider trying

- Discard Zener
- Connect SCR gate to 10 uF with a series R.
- Place a cap from gate to ground.

R >> 10k main R. Gate cap and res time constant need to be probably 5+
time constants of main RC - depend on gate voltage etc.

- Place a diode from gate to SCR  Anode. Diode Cathode to SCR Anode.
Schottky would be better. (This discharges gate cap t below 1 Vbe at turn o=
n.
(Note that real SCR and pseudo SCR may have different gate impedances
in and out which may need some extra thinking)

- Series R from 10 uF to LED to slow discharge rate. Maybe 1K
- SCR holding current MUST be less than long term on state current.

- Your SCR's on/off characteristics could be modified with more circuitry.

- A 2 transistor classic Schmitt - which this is arguably a subset of
- will give you total design control of off and on. It will then be
able to be designed to LED flash without any other parts (probably).

- The classic 2 transistor PNP/NPN flasher / pulser circuit is a
subset of the above and will self flash when voltage is applied to it,
so it effectively provide your solution.

Typical version here.
Can be done without diode.

   http://blog.makezine.com/archive/2006/07/two_transistor_led_flashe.html

Many variants here

                     http://www.techlib.com/electronics/flasher.html

Two x NPN flasher here

   http://www.scribd.com/doc/2158601/Two-Transistor-Oscillator-LED-Flasher

Wow !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Most of theabove seem to be mentioned here.
And many many many more.

          http://www.hobbyprojects.com/F/Flashers_and_Blinkers.html

- Rather than commenting on Olin's social inadequacies it would be
easier for you to filter out messages directly from him. You will
still get messages with his name in which may be easier for you to
ignore. It's possible that the horse will sing, but filtering is
easier.
The advanced master could do a pre-processor substitution that eg
substitutes all mentions of "Olin" with "think peaceful thoughts" or,
less obviously, perhaps, with "perhaps" or "it has been suggested" or
"some wise and noble person has noted" etc . Won't always scan, but
.... .

- You can consider learning from Olin's input, and also consider
whether there is anything worth learning from his input on any given
occasion. Whether there is will vary with what he says and what you
perceive.

In this case your sublinks were labelled "SCR" and "Probe", so most
people will sus what they are about nearly instantaneously, and Olin
did still look as he made a useful comment about the SCR holding
current. The comment may or may not have been technically correct but
gave useful food for thought.


    Russell
--=20
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