Reply and side question RE: data diodes

From: Ed Kennedy <ekennedyx_at_yahoo_dot_com>
Date: Sat Dec 02 2006 - 22:52:21 CST

Hello Charlie,

        I'm a civil engineer and not an electrical engineer so perhaps I
don't fully know what I'm talking about, but generally if an LED has only
two wires to it, and no obvious common ground, I know it will likely do only
one thing (at a time). BTW, we now extensively use massed LED's in our
traffic signal heads because they are so wonderfully efficient and long

        I do have a question about the device you mentioned below and I'd
appreciate it if you could write me a side letter on it. We currently use
inductive loops or video cameras as presence detectors on traffic signal
installations and these things can be a nuisance to install and maintain.
Would the device you described below first of all be adequately bright for
use in a traffic signal light? If so, could it also be used as a presence
detector? It would be nice if we could combine the two.


Edmund R. Kennedy, PE
10777 Bendigo Cove
San Diego, CA 92126

-----Original Message-----
[] On Behalf
Of Charlie Strauss
Sent: Saturday, December 02, 2006 3:11 PM
To: Open Voting Consortium discussion list
Subject: Re: [OVC-discuss] data diodes

Alas, optoelectronics is not so simple. HP and others make things
that look like LEDs that contain both an emitter and a detector. So
one is not home free pointing to an LED and saying well that only
emitts but does not get a signal back.

I think the four wire vactrols are quite convincingly unidirectional.

On Dec 2, 2006, at 2:29 PM, Ed Kennedy wrote:

> Hello Charlie:
> The problem is simply a one of confidence. The devices you propose
> are probably very efficient and trouble free. However, one needs
> to be able
> to take a pointer to the device and say, "See that little thing there?
> That's where the data comes from. See this other thing over
> there? That's
> where it goes. There is only one light and things can't go
> backwards, see?"
> Cynics could wonder if there is something else your little black
> boxes do.
> --
> Edmund R. Kennedy, PE
> 10777 Bendigo Cove
> San Diego, CA 92126
> -----Original Message-----
> From:
> []
> On Behalf
> Of Charlie Strauss
> Sent: Friday, December 01, 2006 8:29 PM
> To: Open Voting Consortium discussion list
> Subject: [OVC-discuss] data diodes
> Looking at Doug's Schematics, I find myself unclear about what
> features of it are so important that it needed to build a device from
> discrete components on a circuit boards. Anyone care to educate me?
> Specifically, monolithic chips that perform this function have been
> available since the 70's. They go by many names, vactrols,
> optoswitches, optical isolators (not to be confused with a faraday
> isolators) or optical relays. One side of the circuit activates an
> led and the other is a photo-cell. Thus the directionality is not
> reversible.
> _______________________________________________
> OVC-discuss mailing list

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Received on Sun Dec 31 23:17:04 2006

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