1. Home
  2. Electronics Design
  3. Need Circuit Design -- Cheap...
  4. Page 7

Need Circuit Design -- Cheap...

On Tue, 05 May 2009 07:25:17 -0700, Jim Thompson wrote: I see I can get that from PCBExpress and get two

Hi Jim, Please understand that this is purely a nice to have, but I would love to have a brief description of the circuit theory / description, such as why the discharge pins on the 555's are grounded. The inverters I understand for the input control line, but the relationshipd between them, the NAND gates, timers, and the transistors used to deal with the flashing I at best have a highly marginal understanding of what these things are doing and why.

I read the data sheet on the 555's and in none of their description for one-shot, stable, or mono-stable uses the discharge hook to ground or really help me undertstand what is happening.

If you want to take a pass on this I fully understand and will not might in the least, as I said, I would just like to have a better understand of just how this thing works and why.

I am just glad it works, to know why might help me in future projects and explain to others that might want to know why it is designed like this, right now I say it is designed this way to make it work, which is true but thin.

Thanks, Bill

Reply to
Bob Thomas
Loading thread data ...

Open drain, unused, could be left floating... old fart EE ties everything down ;-)

It's all logic... if A and B then.., if /A and /B then....

A 555 is nothing more than a comparator with large hysteresis... when input > 2/3 Supply, output goes low, stays that way until input < 1/3 supply then output goes high. Fronted by an RC... it becomes a delay element roughly equal to the product R*C.

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 Stormy on the East Coast today... due to Bush\'s failed policies.
Reply to
Jim Thompson

If you're not in a screaming hurry to get a PCB layout for it, I can put one together for you. Can you read EagleCAD schematics & PCBs? If not, download the free version at: (Your circuit is small enough to fit in the free version.)

Tell me if you want me to make one up for you, because I don't want to go to that much trouble if you'd rather do it yourself. It'll probably take me a few days, depending on how busy I am.

--
    W
  . | ,. w ,   "Some people are alive only because
   \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
---^----^---------------------------------------------------------------
Reply to
Bob Larter

That's a good habit. And yeah, I do the same thing. It prevents nasty surprises. ;^)

--
    W
  . | ,. w ,   "Some people are alive only because
   \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
---^----^---------------------------------------------------------------
Reply to
Bob Larter 

--
No, but I can cite one which you claimed didn\'t but which actually did,
due to the delay through the chip. Remember this?:

      +--------+
Vcc>--|--+     |
      |  |    [R}
      +-|-\\    |
      | |  >---+-->OUT
Vc----|-|+/   
      |  |
     [C] |
      |  |
GND>--+--+-------->GND
Reply to
John Fields

For those interested, I redrew the schematic & created a PCB. If anyone would like to error-check it, here are the details:

Schematic: PCB:

I've made a couple of changes to Jim's schematic. Specifically, I've added a pair of decoupling capacitors, & used a couple of the spare gates to drive indicator LEDs to show when the relays are activated.

Please feel free to comment if you spot any errors, or have any other suggestions. ;^)

--
    W
  . | ,. w ,   "Some people are alive only because
   \\|/  \\|/     it is illegal to kill them."    Perna condita delenda est
---^----^---------------------------------------------------------------
Reply to
Bob Larter

A decent camera will have a jack through which you can trigger the camera photo and reset with a simple relay circuit. But such feature within the camera itself generally makes the camera expensive. A robot clock could also have such a phono jack that would make calibration marks on your charts or whatever. But no one does these things without doubling the price of whatever. They seem to fear people might like their product too much. I think you need a better camera then it will be simpler to build a circuit for using a relay trigger either mechanical or semi conductor not a solenoid to push or whatever. I do not know the brands but they got to be out there for those ubiquitous law enforcement peoples.

Reply to
Geoffrey

Yes, once the details were hashed out Jim did a great jobs as well as some contributions from others. I have a working version not only on my breadboard now but in operation.

Thanks for you input also at the start of this. Poor specs of not it went from concept to working prototype in 10 days, would have hard to complain about that.

Reply to
Bob Thomas

the brands but they got to be out there for those

Thanks for your feedback but the issue was not on the camera side, I did not want the camera's powered or capturing video unless the alarmed system was in the armed state. Even that would have been easy enough to d but the only signal I had to say the alarm was armed was an LED in the alarm box and it had 3 states, off which was unarmed, on which meant armed, and flashing when was armed and triggered, it was this last state that made it more difficult.

As for the camera's they are already set not to actually transmit and the recorder not to be on until a motion detector in one of the camera zones saw motion and triggeres the cams to come on and record, but the trick was to get it to only do that when the alarm system was actually armed and not all the time.

Thanks

Reply to
Bob Thomas

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.