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Need Circuit Design -- Cheap...

Either way is fine. Just don't float.

...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     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson
Loading thread data ...

Good.

Yes.

No. Either would be fine.

When you build it, make sure that you connect each of the 1N4001s as physically close as possible to each relay.

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

Either is okay for CMOS.

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

Yep. Alternatively, he could've also done the same trick using the two spare gates in the 74HC02.

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

Why? the spike originates in the switch that's controlling the relay.

Reply to
Jasen Betts

Negatory, good buddy! The spike "originates" in the relay coil.

Reply to
gearhead

LOL uh... what?

Reply to
a7yvm109gf5d1

Thanks, will keep that in mind for my next project, whatever that might be. Also thanks for looking over the wiring to help double check the connections, etc... Can never hurt to have a 2nd or 4rd set of eyes on these things.

Hopefully this weekend I can tell folks if it worked as planned or not.

Reply to
Bob Thomas

I might get jumped on for having the wrong reason, but from my understanding the spike is generated when the power is switched off of the relay coil, at which time the electromagnetic field collapses and generates an EMF(spike) in the reverse current direction, thus the diode to block and dissipate that spike from hitting the supply voltage rail and everything hooked to it and potentially frying your CMOS parts.

Thanks...

Reply to
Bob Thomas

Thanks I usually mount them right between the coil pins on the relay, if there is room or just in front if not. Thanks for the tips though from this thread I have not really given any reason for anyone to think I have done anything before... I still do a few PIC based projects a year for one thing or another I need, but it has been years since I have tried anything like this. Perhaps that is why is seemed like it should be simple. I guess simple is reletive, if you know what you are doing, many things are simple :)

Reply to
Bob Thomas

Say what? The spike originates in the relay coil when the field collapses at switch-off.

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

Correct. And you put the diode as close as possible to the coil to minimise the inductance/resistance between the diode & the coil.

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

Well, at least we know you can read a schematic! ;^)

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

Indeed.

I'm curious to know how the smoke-test goes. ;^)

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

It all starts at the switch. The wires betwen the switch and the relay also have inductance.

Reply to
Jasen Betts

Get a life, Jasen. The important energy is in the relay coil, _not_ the interconnect wiring.

...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     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

Dude, you need to hit your textbooks.

Of course. That's why you place the diode close to the coil.

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

Damn - I missed it. I hate it when I do that. :-(

Ed

Reply to
ehsjr

Hmmm... I'm not so sure about that.

Ideally there is no "spike" if there is a diode in the circuit. The function of the diode is to allow continued current flow. Any wiring to the coil would also have a bit of inductance. As Jim says this is normally tiny. But if you are worried enough about this to worry about where the diode goes - say it is a solenoid at the other end of a long cable - it seems to me it should go near the switch.

----------------------- | | `----------[Lcable]------------[Lcoil]-. | | --- | /_\\ | | | .--------------------------------------' | [transistor] |

--------------------

--

John Devereux
Reply to
John Devereux

Yes. With a _very_ long cable. If the "cable" is zip cord, it is left as "an exercise for the student" to calculate the energy storage ;-)

...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     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

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