Gus Calabrese wrote:
<snip>
> 4)   Any cool suggestions on power management?
> Gus Calabrese

Gus, light blocking is a nice solution but it requires light,
n almost 100% of the cases it is a power pig solution.

There are some other ways to sense objects without the use
of light.

- sound
- pressure
- physical switches
- infrared sensing
- doppler sensors
- capacitive sensors
- light change (use ambient light)
- weight

What is the material to be sensed inside the tube?

Metal is the easier to sense, while anything warm or hot
can be easily sensed with an infra-red diode. This solution
is generally used at food or any post production as plastic
or extrusion.

Accumulate energy in a long term in a capacitor to use at the
relay will just expend more energy, since the current limiting
device, normally a resistor, will dissipate heat.

Use a latching relay, Digikey has some very nice, and it cost
the same of a non-latching, around $4.00 and consumes 5mA just
at the pulse time that is no longer than 100ms.  To use a
latching relay, just use a regular 74AC.. gate with a polarized
capacitor in between the gate output and the relay coils
connected inverted.  When the gate sources, the capacitor charges
and the current makes the relay actuates, the current drops,
the capacitor holds the charge and there is no more power consume,
until the gate sinks to ground, then the capacitor discharges
over the relay coils, flipping the relay without any extra power
consume.  So to actuates the relay it takes 5mA for 100ms.

To the 74AC... point of view, doesn't matter what kind of relay
you connect there, a regular one or a latching *with* the
capacitor, it is the same, except for the power consume during
the relay "active" state.

The only inconvenience of a latching relay is that you never know
its state (actuated or not) when you power on the unit, since it
retains the state from the last time it received a pulse, except
if you save this in an e2prom.  But generally we use to send a
"reset" pulse to the latching relays right at the power on sequency
just to make sure about its state.

For sure, to "reset" a relay in a configuration as described above,
it requires the capacitor charged, so to reset a relay, you first
need to actuate it. :)  It is very common in portable devices that
use latching relays, when you powers it on, you hear a "click" for
every latching relay inside.

--------------------------------------------------------
Wagner Lipnharski - UST Research Inc. - Orlando, Florida
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