Saturday, November 29, 2014

Student Discovers a Light for a Fading History, Adds Dimmer Circuit

This evening, through careful study, I have learned how to emulate my grandfather's light-sensitive shop-light -- pretty neat, one might say.

Personally, I would use a solid-state relay (SSR) in the mains-facing part of the circuit -- perhaps, in a circuit similar to that illus. p. 3 of the data sheet for the Sunrom LDR 5 mm, in which the current across a photoresistor provides -- in inverse proportion to the intensity of the light source -- a current to the base of an NPN transistor. In the circuit as described in the data sheet: When during the daylight hours, the sun's light would be of a greater intensity, then the photo-resistance would be lower, in the circuit, and the transistor would have a base current. With an NPN transistor in the circuit, the circuit to the base of the transistor effectively activates a relay, namely when the photoresistance of the photoresistor reaches below a certain value, in an inverse proportion to the intensity of the light source. There's to a theory of operation of the item.

As far as an implementation of the manufacturer's original circuit design: If the variable resistor was to be implemented with a dial, then a variable resistor might be selected with an "Inverse slope" for the gradient of the variable resistor -- for the dial's setting, then, to appear to be in direct proportion to the light sensitivity of the circuit, in the original construction?

Substituting a PNP transistor into the circuit -- with a small translation of the schematic, for the current pathway, in the PNP construction -- the current to the base of the transistor would have a functionally opposite effect, contrasted to the design as in the schematic.  With base current to the PNP transistor, the relay would be deactivated. With photoresistance at a maximum, then -- as when sunlight, as at light source, would be at a minimum -- then the base current would be at a minimum, and the relay would be activated, in the alternate PNP circuit.

If the variable-resistor was implemented as a dial, comparatively in the PNP construction, then perhaps it should rather be placed on the collector, along with a similar, static-value resistor there -- that circuit branch, then replaced by a ground wire, in the schematic -- and likewise implemented with an "inverse gradient."

Insofar as type of relay, an SSR would certainly allow the relay portion of the switching circuit to last for a while -- as contrasted to a circuit with, instead, a mechanical relay. If there would be an SSR element of sufficiently compact design, then perhaps it could be implemented all within a base for a light bulb -- or alternately, in a grounded enclosure, with a two-wire cable leading to the base of the light bulb, perhaps to something cleanly done for a residential application ... if only that could all be done in an AC circuit, without any further translation of the manufacturer's original design.

In an AC implementation: The relay would provide an interface to control the AC portion of the circuit. Secondly, there would need to be a DC current source for the switching component of the circuit -- perhaps, something that could be made with a simple, full-wave bridge rectifier -- between the relay's switching component and the rest of the circuit -- with capacitors sufficient to smooth the rectifier's output waveform to a nearly linear current. If that would be all patented-up, already, one could put an Arduino into it, wire it for IoT, and call it "Public Domain," or optionally under some kind of a formal license. "DIY engineering," the poor engineer's alternative to patent litigation. 

I'm sure it's all been done more efficiently, already, but there's a thought to how it could be done, nonetheless. Schematics might ever appear, here, if there's ever a place one would put such a thing.

What one might also say: If I had a shop or a house to emulate it unto, that would be even more nice? If my parents even had a house of their own ... then that would be different than how this year has been, in my family's life. But now, I can emulate a light-sensitive light switch for a disappearing history, for however long the light switch would last. How novel. The things I might make if I was an electrical engineer could outlast my family's own rustic pre-consumer heritage, until it's all been consumed by the consumerist "Modern". What good would that be?

That someone later could put it into a museum and say it was not how it was? That I myself could try to paint any too bold picture of our simple, rustic origins, to entertain any too-bold "old west" romanticism going by? Or that it could just dwindle after the shop light burns out -- that's how I imagine it'll go.

I had seen one of something like the Sunrom LDR 5 mm, once upon a time. I will not ever again see the house I was raised in, and neither the house in which was my grandfather's family. This is the life I know.