Wireless switch for power

  Thank you Michael.....that may be useful. I had a meeting with someone knowledgeable in this field and I think we are going to make some progress. I will post any solution if we can come up with one. Thank you.

Thanks Don......sounds like Latin to me.

Okay, I will be more verbose, maybe I can snow us both under, it certainly is blanco outside here in the Chi!

An opto-isolator is a device that can be described in many ways, I don't want my POV to seem exclusive.  It isn't even with me.

What one gets with an opto-isolator is the ability to separate power supplies.  Your processor/controller is a slab of semiconductor, unless you are poor, Soviet, and in the disco era.  Then it is spread about on four slabs.  Nowadays its the other way, sometimes, multiple processors on a slab.  Your power transistor, nearly invariably, nowadays, an N-channel MOSFET.  This is if you are trying to replicate an SPST switch.  Is also made of thousands of transistors.  'cept these are all alike and in parallel and series with their gates (control terminals) bussed.  Still, its an LSI.  The currents and potentials and loads that modern power transistors are rather amazing.  Since our Q is in the high-current regime, we are sure to have a positive temperature coefficient in our main conduction channel, the clappers on the switch.  This means if we want even more current, we can parallel our power transistors.  Now the only limits are the wife's pocketbook.  Even a fart or hiccup from a power system can entropize sissy-pants CPUs in this situation.  Let's look at the situation where we have a simple stepper motor driver driving a stepping motor with a mechanically reactive load.  Let's say our load is asymmetrical and out of the gravitationally normal plane.  Now, our motor must move and sometimes restrain the load.  We energize and refrain from energizing our coils in our stepper motor.  Now, normally, if one was using a solenoid-actuated-valve to irrigate the rosebushes when one was on vacation, one wouldn't care much about spike dynamics.  When the plunger is de-energized, it snaps back violently, changing (water flow) state given a first-order valve design.  We don't really care about this as a mechanical proposition 'til we are dealing with valves profoundly out of proportion with rosebushes.  This implies that our anti-spike could be a first-order constructed of a diode.  But with the stepper motor in this particular case, I am motivated to let the spike-back current out of the circuit more slowly.  There are  circuits made with Rs. Ds, Zds, Cs and even Ls and Ts, if one is a conservation-freak, that can do this.  This conflicts with my desire to avoid soft- and hard- faults in my controller, however.  I want my controller to be a confident little dictator, in an electrical lair.  The first way to do this is to make sure you have a fast uF-ish scaled decoupling capacitor across your device.  If you put any bulky-bulk on your board, consider a backwards shottky diode across it, for the power-down circumstance.  Really bulk users, like large audio PAs have to use relays and resistors and thermistors during power up/down to minimize current and dissipate stored energy, I digress.

When I impose an opto-isolator in my circuit, I get to use another power-supply.  Generally an isolator would go to a different form of energy than electricity as an intermediate:  A transformer uses the magnetic (thank Thoradson) field.  The energy inserted and extracted from this device is, ideally, in phase.  Transductor is the same thing,'cept the extraction is 180 degrees, ideally with the imposition.  Capacitive transformers use acoustic energy, but seem to have fallen out of fashion.  An acoustic pair can use ultrasound and be bidirectional.  RF could work although conceptually, it is just using a weekly-coupled transformer.  Light is an obvious medium.  So an opto is something like a photo-diode aimed at a photo-transistor in an encapsulant that is opaque.  Susceptible to radio-active decay, but opaque.  The LED is a two-terminal device, the photo-transistor is presented as a three-terminal device.  The original version wasn't DS fast.  You could make it fast.  You can current feed the devices, you can keep them out of saturation, and you can use positive feedback.  If the winter keeps up, I might be doing that for  grins.  Market progress has integrated the follow-on discretes:  Now our device, in this case is saturating (read digital -- or Schmidt) and features an ideal topology for an output, push-pull.  If you miss TTL, you can always put a diode and resistor!  The output stage can handle a fair amount of current, and it can source or sink current.  This is ideal for jocking the control terminal of an SPST device, a push-pull pair or half of an H-bridge.  Because, the control terminal of a big MOSFET, or three, is essentially capacitive if we are doing things rightly.  So, we could construct, say, our own solid-state relay out of just the opto, the powerQ and a few miscellaneous passives and connectors.

=============Don't read this if you already know how to ballast an led or you will get a headache, and you already know how==========

Meant to type: DC solid-state relay, getting sleepy.

So we only want to do 1 of 2 things at a time with this particular opto. It isn't designed to operate in a linear (continuous) mode.

-not energize the input led

-energize the led with 8.75 ma of current, in the proper direction.

If one were to give a kid a bargain-bag of LEDs and a drawer-full of miscellaneous batteries, and he caught on to the two-terminal nature of the sources and loads, different things might happen:  He could destroy a given LED in a flash of light.  He could destroy a given LED without a flash of light.  He could hook up a battery without result.  He could steadily illuminate a LED.  If this last happened, the battery was nearly exhausted.  Its Thevenin equivalent resistance grew large, as its voltage fell.  If the voltage falls below the threshold voltage of the LED, still no soap.  The first-order model of a battery is an ideal voltage source with a series resistance.  They have to put this resistance in at the factory, else a clumsy mechanic could destroy the universe.

So the chip implies that we must insert a resistor between the front-end of our opto and a driving potential (voltage) source.  We gotta make our voltage supply look like a dying battery to the LED or it will fry.  LED not linear in effort/flow.  Double the woltage, bring up the current by a factor of ten.  All diodes are LEDs.  Some are cruelly encapsulated in dark epoxy.  Some are so low in frequency (and now high!) that they are hard to see.  LEDs tend to be monochromatic, and wavelength is inversely proportionally to the drop.  Red LEDs have about 1.2 V drops (xout voltages), Violet, about twice that. We are figuring upon about a volt and a quarter of drop, cause its late, and when its late, I like to keep the math easy.  If our logic supply was 3.3V, and our outputs were CMOS, we could probably take our choice of turning on the LED when we go to the positive logic true state, or vice versa.  Pulling down to activate might be slightly better electrically, but not worth fretting over.  If our driver is TTL or nMOS, we wanna pull down.

Anyway, our LED has a potential of one-and-a-quarter, say.  This means (forward mode) in order to operate but not too much we expect such a drop.  We need to subtract this from the supply voltage, then whip out hoary old Ohm's law to wind up with our R's value.  R=V/I (think about it, more effort, more flow)

--Is that right, darn it's late!  3.3-1.25 = 2.05! ***! R=2.05/8.75*1000  = 234and a quarter, about!--

We're not done, bucko!  We still need to reckon the power we intend to dissipate in the ballast R in the active phase:  Power =IIR =(7/8/100)^2*234 (circa)

To the fella who wanted to move a bolt:  If your reach is about greater than a quarter-inch, consider a stepper-motor with integrated leadscrew.  Bear in mind that you can use micromachined sensors to tell if someone is sawing or filing on your bolt, nowadays, just sayin'.

     Thanks again Don........

           I am having a designer look at what I need to have done...........if everything works out the way I want it to, I will let you know what he came up with.

                    Thanks, Keith