On Sun, 26 Jan 2014 21:54:48 +0000 (UTC), Kaz Kylheku
wrote:

On 2014-01-25, Jerry Peters wrote:
dave wrote:
On 01/23/2014 06:05 PM, Michael A. Terrell wrote:

dave wrote:

On 01/23/2014 06:45 AM, Michael A. Terrell wrote:


It is not a switch or a valve.


It's a solid state diode that oscillates. DC in, and ~10 GHZ out.
Search on Gunnplexer. You see them on automatic doors in almost every
store. A microwave mixer diode takes a sample from the Gunn diode and
compares it to any reflected signals. This results in a low frequency
signal that is detected, amplified and signals the door to open. How can
a passive diode do that?


Like I said. You can hit a piece of quartz with a hammer and it will
oscillate; that doesn't mean it's considered and active device. An
active device uses one signal [current, voltage] to control another. As
in amplify or switch. Thermionic valve, transistor, SCR, Triac is what
we are going for.


An active device uses one signal [current, voltage] to control another.

So a relay is an active device?

We should probably apply the "active" or "passive" designation to circuits
rather than devices. When we say that a device is active, it means that the
only sensible way of using it is in the role where it provides an active
circuit.

A passive circuit is one in which the energy source for driving the output
signals is derived from the input signals, rather than from some auxiliary
power supply.

Anything else is an active circuit.

Because the energy for driving outputs is derived from inputs in a passive
device, a passive device can never amplify power; though if it contains
inductors, it can step voltage up or down and thereby modify impedance.

A logic inverter circuit built on a relay is definitely active. Justification:
the device produces an output which is based on the input, but which does not
draw energy from the input at all to power the output. Power is applied to the
switch, in series with a load resistor. This energy source is not considered
an input signal.

If the relay's switch is used to pass through or cut off a signal (say as part
of a multiplexer), then we can regard it as passive. When the signal passes
through the relay, it does so without amplification: the output is powered by
the input. The next and previous device are not isolated from each other's
impedances in any way by the relay; it is transparent. Moreover, the relay's
coil is powered by *its* input: the switching mechanism itself does not have
its own source of power.

(Note that by the same logic, we could argue that a FET used for signal
switching also gives rise to a passive circuit.)


And just to trip you up,what about USB to TIA 232 converters?

?-)