VC ADSR (555 pin 2 vs pin 6)

[Toby Paddock]

I remember years ago something about 555's from different manufacturers 
having different ideas on who is the boss, pin 2 or pin 6.  
If 2 was low and 6 was high, the two types would act different.  
Or something like that.  Probably doesn't relate to this, 
but it triggered some old memory cells.

 - -- -  Toby Paddock
http://www.seanet.com/~tpaddock



tomg[SMTP:vco at mindspring.com] said
> Hi Guys,

Hey Chris,

> > >I like your transistor input circuit. Was Chris' schematic wrong about the
> > >trigger in on the 555? I thought it needed to go negative...
> > 
> > Wellllll....yes. You are correct, Chris' circuit trigged on key up not key down.
> > That is a little unnatural feeling. I'm sure he would have gotten that fixed.
> 
> Not sure what is meant by the above.  Here's how the 555 works in my
> circuit:
> 
> Trig   Thresh   Out
> ----   ------   ---
>  0        x      1
>  1        0      1
>  1        1      0

When pin 2 of the 555 goes low it triggers. Sending a positive going gate through
a non-inv amp at pin 2 can cause multiple triggering. It doesn't really see pin 2
go negative until you remove the gate. 

Using the cap coupled transistor...the gate goes high, pin 2 sees a high going 
pulse and triggers as it goes negative. The 100K resistor holds pin 2 high until
a negative going pulse is detected, to avoid false triggering.

-tg