One transistor timer

Archilochus

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Hi Richard,
Thought I'd start a new thread as the other one was starting to wander a bit.  I cooked up this little circuit based upon your idea and some old books I have.  I posted it with a brief description at:

http://www.geocities.com/archilochus57/q_timer.html

You'll need to experiment quite a bit with component values to get the timings you want, but it might work for you.  Certainly a lot easier to explain to your son.  Radio Shack has booklets on the 555 that explain their workings - you can also find lots of info with the various search engines or even ask some questions on relevant newsgroups such as sci.electronics.basics

Good Luck,
Archilochus
 

Richard Webb

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Arch-

Thanks for the help.  The cam is out in the field right now, so I must wait until this Saturday when I take the boat out again.  The 49-425 wants to be warmed up in the off position, so I can't cut the power off with the one transistor timer.  But, I could break into the existing PIR alarm/off/chime switch with an opto (or relay) that would put it in the off position for a minute or longer.  That delay could be used for a warm-up period when the PIR is first turned on, and also between pictures.  Is that a good idea, or is there a better place to disconnect the PIR Sensor?

I like your webpage.

(Edited by Richard Webb at 2:17 pm on June 6, 2001)
 

Richard Webb

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Hi Arch-

We had beginners luck, and got some nice pictures of a couple of fawns.  Now, I'm wondering if it's a good idea to use a timer with a doe & 2 fawns strung out like that?  The repeated snaps caught them all.  Can we switch out Cx & Rx, and still use the Gate (2N002) to key the relay?  
 

Archilochus

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Sure, just put a switch between the cap and the gate.  Open the switch and the relay will follow the pin #2 output so you'd get multiple pics (that is more or less what Tinhorn suggested when he said to use the pin #2 output of the big IC to drive the transistor that is already on the 49-425 board).

There are some problems with the one-transistor timer though.
I've heard that the Owl cams will shut down if you hold the shutter pressed for more than about 3 minutes.  So you'd need a second timer stage that only gives a brief (3 sec or so) pulse for the shutter at the beginning of the pic interval time.  I think this is an old problem that Tinhorn and others have been working on - resulting in his (and others) "two-stage" timer circuits available from  Jesses' camera page.
The other problem is that the one-transistor timer is "retriggerable" - which means that if an animal trips the PIR and starts a time delay (say it's set to 5 minutes), but moves back in front of the PIR every 4 minutes, this would reset the timer to zero each time the animal came back.  You could conceivably end up with a time delay of 20 or 30 minutes!  You'd need some logic at the front end to "lock out" the input and keep the circuit from being retriggered.  But if you start doing that, you might as well go with the 4047B or 4538B timers which can be configured to be "non-retriggerable"

While the one-transistor timer seems simple at first, it's not really all that useful for our purposes.  It's more of a 'demonstration' circuit to show the general concept behind the more advanced timers.
>>>>>>>>>>>>>>>>>>>>>
Good job with the pics!  Took me something like a month to get my first pics when I made my first cam.
 

Richard Webb

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Arch-

School is out next week, and my wife is a teacher.  That surely will put a crimp in my electronic gadgetry.  One idea that I had was to use the one transistor timer to break contact with the shutter for a brief time, just before the 3 minute time limit when the Owl shuts its self off.  After getting repeated pictures of a doe & two fawns I may need this feature.    
 
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