How to create nontriggereable monostable wit a counter

Thread Starter

loconel

Joined Aug 5, 2010
4
For an infrared based webcam on a battery I need to trigger the following sequence initiated by a PIR (5 volt) at night:
  1. illuminate the object for 5 sec (Save battery-energy)
  2. trigger the smartphone to take a picture
  3. Do not take a picture during 600 sec. (Save battery-energy)
See the attached schematic.
  • I designed a 600 nonretriggarable monostable 555 for step 3 by realizing a 600 sec positive pulse with the U2 NE555 block monostable started by a movement detected bij the PIR
  • At the same time the object is illuminated for 5 secs. A 5 sec positive pulse is realized by the U4 NE555 monostable for the illuminator.
  • With a delay of 1 sec the webcam is triggered to take the picture ( positive pulse width 1 sec). Circuit not shown.
To realize all this I need 3x 555 and a number of passive and active parts.
I hope I can realize this by a nontriggerable digital counter. It means a lot fewer parts
Any suggestion?

Mobilewebcam.jpg
 

AnalogKid

Joined Aug 1, 2013
10,987
If you already are familiar with microcontroller programming, such as PIC or Atmel part, that is the lowest cost and easiest way to go. If you want an all-hardware solution, it might take two counters. The first one enables the second one briefly, then disables it for 5 minutes. The second one is something like a 4017 that can turn on the illumination, then trigger the camera, then wait, then turn off the illumination. All of the timing can be decoded from one counter such as a CD4060, but the number of gates and the decoding complexity might exceed a two-counter approach.

OR, one long counter and a dual flipflop such as a CD4013. Hmmm... That might work. But in either case I don't think this is a 1-chip problem.

ak
 

AnalogKid

Joined Aug 1, 2013
10,987
*trigger* after 1 second. The exposure might take much longer to complete.

I have it down to three chips, a 4060 for the 5 minute lockout, a 4017 sequence stepper, and a gate package that forms a reset enable. Turns out that while having a counter reset itself is easy, having a counter disable its own reset input has to be grown externally. The only quirk is that the system runs on power up, so triggers are ignored for the first 5 minutes.

ak
 
Last edited:

Deleted member 115935

Joined Dec 31, 1969
0
Using a processor would be a more usual way to approach this problem,

An off the shelf arduino board like the teensy 3.2 would be a good starting place,
lots of support, an easy system to learn,USD 20 for a board ready to go,
 

Thread Starter

loconel

Joined Aug 5, 2010
4
*trigger* after 1 second. The exposure might take much longer to complete.

I have it down to three chips, a 4060 for the 5 minute lockout, a 4017 sequence stepper, and a gate package that forms a reset enable. Turns out that while having a counter reset itself is easy, having a counter disable its own reset input has to be grown externally. The only quirk is that the system runs on power up, so triggers are ignored for the first 5 minutes.

ak
How do I configure the 4027 as a nontriggerable monostable. I think that is your idea? Nontriggerable because I have to block additional random triggers in time from the PIR during 600 sec.
 

AnalogKid

Joined Aug 1, 2013
10,987
My idea is based on your original question about using a counter rather than timer chips. The 4027 is a dual flipflop. Did you mean the 4017?

ak
 
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