tinhorn's timer problem

warrendsga

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Hello,

I've been building the 2 sec/3 min timer from the "How to Make a Two Stage Timer Board" post.  Everything is hooked up like the pictures and diagram shows but when I apply the test per the directions, the 2 sec LED lights but the second stage never drops back to 0 volts in order to retrigger.  I'm using brand new timers and all the values are as the diagram shows.  Please help if you may have any idea what's going on. Thanks!

David W.
 



Tinhorn

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Warrendsga

I assume you double checked and triple checked the wiring a hunnert times already.  I can only make a guess at the problem, either something didn't solder or there is a solder bridge or something was installed wrong.

One of the Pix's of the board has "Tests Voltages" given for all 8 pins of the TLC555 (figure 4, the one with the Red Clip Lead attached)  

Check these if you have a volt meter.  On pin 6/7 you should see the volts slowly increase as the timer counts down the delay (when those pins reach 2/3 of Batt volts, the counter resets and is timed out)  

Note, your volt meter will affect the count but not very much if it happens to be a digital.  If it's counting but stalls before reaching 2/3 batt volts then maybe the cap is leaking off the volts, try to replace it with another, I had one bad right out of the box, but it could be your meter draining off the current making it stall BTW.

Hope you find something "easy"...

Tinhorn
 

warrendsga

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Tinhorn,

Thank's for the speedy reply...I feel like an idiot.  I found that the axial cap was reversed.  I fixed that and evrything seems to work until after the second stage goes to 0 volts.  The directions say to ground the trigger to re-initiate the 2 sec / 3 min sequence.  When I do this, the 1 stage LED doesn't come on but the volt meter reads 7.8V (I'm using a 9V system) for 2 minutes and then goes back to 0V.  The instructions say that the LED is supposed to come on again.  Any thoughts?  

Thanks for the input!

D. Warren

PS- This site is great, you'll have me hooked.  Built 1 cam already (owl pf w/ rs pir) this is for my second using a ms20.)
 

Tinhorn

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Dave

Glad to hear you found the problem.

Does the LED ever come on, if it's reversed, it won't come on, try to reverse it and see what happens.

Another thing is to check the resistor value attached to it, for 9 volts, it should be  500 to 700 ohms  if it's a standard LED.  Any less might allow too much current to go thru it and burn it out, especially when it's on for 2 mins....

Good Luck with it

Tinhorn
 

warrendsga

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Tinhorn,

The led does come on for 2-3 seconds when the battery is applied.  Then the 1st stage goes for 2 minutes at 7.8V.  It just doesn't come back on when I place 0v at the trigger momentarily.  I'll try changing the resistors to the higher one and see if that helps.  

What actually re-triggers the  second  (2 sec)  stage LED.  I know that pin 2 is the trigger but is it waiting for a signal from the 1st stage?

I can send some up-close .jpgs of the board if it'll help.

Thanks!

warrendsga
 

Tinhorn

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Dave

The transistor between the 2 stages is what triggers the 2nd one.  A trigger "Pulse" travels thru the .0047 (.005) capacitor and triggers pin 2 of stage 2.  You won't see this pulse on your volt meter because it's too fast.  

Here is why the Transistor is needed:

(The Timer Output is a High (near Batt (+) but the trigger needs to be "LOW".  The transistor "Inverts" the High to a Low, which goes thru the .005 cap and triggers stage 2, get it?)

NOTE:

These timers will "NOT" time out as long as the ground on pin 2 remains.  All it takes is a Momentary Ground to trigger the timer, the cap only allows a pulse to get thru to pin 2 and blocks the 2 min's of "High" from stage 1.


BUT, Stage 1 TRIGGER has no cap:

I didn't think one was needed here because the trigger from the PIR isn't 2 mins long.  (BTW, these timers don't reset and start the time delay over again if another triggers arrives before 2 min's is up, they are "Non-Retriggering&quot  

That resistor going from pin 2 up the batt (+)  (of stage 1)  is a "Pull-Up" resistor, to insure pin 2 volts remains high when no trigger pulse is on it.  It's just here for insurance....

******************************

Look at all the new terms you learned, Pull-Up Resistor, Trigger Pulse, High/Low, Invert, Non-Retriggering

Building the circuit will make you Learn all kinds of stuff about electronics and electricity and it's fun to figure out how and why they work.....

See Ya!

Tinhorn
 

warrendsga

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Tinhorn,

Last time and I'll stop botherin ya,  

I hooked everything up the way the diagram shows.  When I close the switch to the battery the LED connected to IC2 lights for 2 sec and goes out.  The volt meter goes from 0 to 7.8V for 2 min then back to 0V.  I then take a lead from the -batt lead and briefly make contact with the R2 lead per the picture.  The LED connected to pin 3 of IC 2 doesn't come on at all but I notice that the voltmeter goes from 0V back up to 7.8V for another 2 min.  It's like it's skipping the 2 sec IC2 completely.

FYI I momentarily grounded the trigger to IC2 and it triggered the LED.

I'm stumped.

Have you ever seen this behavior?


FYI I'm a mechanical engineer trying to learn electronics..that's scary!
 

Tinhorn

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Dave

If you watch the volts at Pin 2 of IC2 (with your volt meter) , I'll bet you see it goes to near Zero when IC1 is triggered, and stays there for 2 min's.....if so, there is something wrong at the transistor circuit area.  Check Cap wiring and be sure Tranisitor Leads are connected to the proper place, etc

Hmmmmmm

Tinhorn
 

warrendsga

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Tinhorn,

SUCCESS...

I swapped out the transistor with a 2222 and it looks like it's working fine.  Now I finished hooking up the reed relay and switches.  Seems like it doesn't want to trip the 5v reed.  I measured voltage from pin 2 to ground and it seems like it's only putting out 1.8-2 Volts. (noy enough to throw the reed).  Ever heard of that?  I'm going to go back and double check for the tenth time...keep ya posted.

Thanks!
 


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