2 Stage Timer Theory

Matt in MO

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I completed my first timer (from Kevin May's kit) and I think it works! It's Tinhorn's first design where the first stage is the 2 second shutter closure. When this first stage sees a quick trigger to ground (via a relay) it holds the shutter relay closed for 2 seconds, times out, then can't be activated again until the second stage times out. fine.

But, if the trigger to ground is held constant (relay is kept energized) the shutter relay is also held closed constant. Is this correct, and if so, is this a problem with the RS PIR?
 



Tinhorn

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Matt

U R Rite......that's a problem

As long as pin 2 of the TLC555 (or plaino 555) timer is grounded, the output stays energized, the timing cycle won't work unless pin 2 ground is "Removed" before the time delay is up......

That's why there are some components on Pin 2 of the 1st (2 sec) stage, they prevent full time grounding of pin 2.

so

Double check the .0047 or .005 Capacitor and 1 meg resistor in parallel with the cap  (C1 and R1)   and also check the two 37K resistors connected to pin 2 (R2,R4)  If they are wired ok, check the 1 meg resistor (R1) and be sure it's "1 Meg"  (Brown,Black, Green)  This resistor value is so high, it's almost like it's not there, not enough trigger volts can get thru it to "Trigger" the TLC555, it's only there to bleed off the charge of C1 when it gets triggered ( a cap can stay charged sometimes, and cause problems)

The cap (C1) will only allow a "Pulse" from the PIR to get to pin 2, no matter how long the PIR relay is triggered, it grounds pin 2 only momentarily.

Tinhorn
 


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