[GreenKeys] tuning fork frequency?

[Peter Gottlieb]

You have to use a bridge for both frequency and reverse voltage issues.  
Take a diac from an old dimmer and put it in series with the resistor 
and it will increase the strobe contrast.  If you can't find a diac put 
the highest voltage zener you can find in series with the LED.  The 
point of this is to use what you can find laying around so it is a free 
add-on.

If you want to be more in tune with the technology of the times, use a 
neon bulb.  This will give a very nice strobe effect.  Remember the 
turntable speed check discs with lines printed on them for use with a neon?

Peter



Ken Schwieker wrote:
> There is a problem with the LED/resistor strobe circuit in that a 
> LED's reverse max voltage spec (usually around 5 volts) precludes 
> having the 140 volts on the non conducting half of the cycle getting 
> to the led. A blocking diode should work to keep this from happening. 
> Another better option would be to use a bridge rectifier which would 
> in addition to solving the reverse voltage problem, give 120 blinks a 
> second verses the 60 with a blocking diode. The blinks from a LED in 
> these circuits will be rather drawn out which will result in a smeared 
> target view. Since any useful strobe effect will work this probably 
> makes no difference.
>
> Ken S
>
>
>
> >Thanks for the help with the Teletype tuning fork question.
> >
> >I believe that 120VPS is the correct number for a Model 28, the 
> 87.6VPS number is for a Model 15.
> >
> >The LED/resistor wired across the AC line is an ingenious idea.
> >
> >Dave Ross    N7EPI
>
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