One transistor timer

[Archilochus]

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]

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]

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]

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]

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. ### ###