Author Topic: Optical Bench REDUX: Digital Switching can have Analog Functions!  (Read 26304 times)

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Offline RJHayward

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Hi there:
   Continued from previous thread, on using Solar Yard Lights, for investigating various switched networks, without interconnecting wires.
   Having some difficulties, getting (proper) experiment settings, and especially, focus on 'edge trigger' logic.  The gist of this is, a solar light contains a (digital) switch, for only operating at night, by using the very same little solar 'panel' as a light sensor.  So, in digital terms, you have a means for 'mixing' various inputs, that are then combined into a totalized 'analog' input, for the level check.  If threshold is exceeded, that means the solar light is now in substantial (ambient) light and will shut off the LED output.
That is basically a 'logical NOR' gate, obviously also useful for 'And gate' functions, equivalent.
  An interesting aside to this; the little yard lights can be operated / switched, by application of two signal 'inputs', optically, where each input is (barely) above
50 %. There things, roughly speaking, can start to resemble neurons, where various input synapses bring analog coded signals for combination.  Of course, there isn't any 'negative' polarity of light, in same sense as electric, plus and minus, but the meanings can still be carried: Most signals, into the solar light, are 'inhibitory' anyway, and inverted logic can conveyed, this time by presence, or lack of presence (of any light).
But in general the inhibitory and actuating aspects can both be expressed, in collections of yard lights, into various relation structures, (like a simple 2-state flip-flop).
   Picture shows, a causally built 'Optical Bench', having top with many mounting holes, for putting gates (yard lights) individually related.  Underneath, is provided various battery packs and solder less proto boards.
A LED blinker provides a light source, for some testing.
 
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Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #1 on: April 21, 2022, 07:25:25 pm »
In this enclosed photo, I'm showing the difficult process, of obtaining a decent 'EDGE TRIGGER' on the light beam, from a first 'gate' and to the left, is seen a second gate, meant to be an inverter, in a classic edge detecting circuit (although here it is optical, not electric).  Problem was, mainly with various light levels, in that little, 3 component circuit.  For solving that, edge detector circuit, it was necessary to separate the solar panel (optical input), from the direction the output LED is pointing.  This way, the third gate, will get the full LED output, even while that 2nd gate is no longer inline...the output direction has been manipulated, just do that mechanical alignments are correct (for transfer of enough light to cause switching).
   If all that works, should be able to reproduce those very short pulses of light output, that I've already verified, (but on more 'shakey' informal experiments.)
The classic principal is simple: A delay through an inverter causes a short 'AND' condition to be satisfied, so an electrical pulse output happens. Then, as the inverter catches up, in matter of nanoseconds, the AND gate output goes 'false'.
 
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Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #2 on: April 21, 2022, 07:27:10 pm »
This photo showing the transient light (gate on the left) is off, in this view.
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #3 on: April 21, 2022, 07:28:43 pm »
(this view) shows the transient light gate inverter, with LED output ON.
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #4 on: April 21, 2022, 08:41:10 pm »
This current photo shows a kind of dual-nature, in the sense that, in upper, first example it's all digital, gate to gate, while second example, (lower in photo), shows two inputs, reaching the 100% threshold by combined intensity of light input. 
   So can have either, it really depends on context of use, whether you are getting a 'NOR', (with equiv AND, of 'not' inputs), or you are getting a 'NAND', style, where both inputs are needed, to get a logical output (zero).
It's a bit muddied, by the mixing of analog terminology, for inputs, unusual, with typical digital resolved output.

   For more 'context' illustration, a good example can be a design, for an optically sequenced A to D converter, acting to monitor ambient light levels.
By running a 'calibrated' light source into a gate, for comparison with ambient levels, it can be determined when the threshold is crossed, of a TOTAL light input.
So, let's assume today's light is at '30 %' ...an arbitrary number.  Then, by essentially adding in a D to A generated 'light' signal, the 100 % threshold is crossed when your D to A output climbs up to 70%. Thus you get a reversed or inverted answer result that can easily be inverted, to the correct result, of 30%.
The method is classic A to D by creating a source, via a D to A, for comparison.  Either a ramp style, (slow), or a successive approximation style can be used, in the A to D scheme.
   For the OPTICAL A to D subsystem, each of 4 bits are  (individually) raised, then tested, against AMBIENT, and subsequently canceled, if the trial (light level) went too high. That happens 4 times, for each bit (weight).
At the end, you have a 4 bit result, inverted, but it's an analog measure, of ambient light level.
The sequencer and test logic involves some thing on the order of 40 to 50 of those little yard lights.  Makes for interesting and intriguing exploration of digital analog, and neurological concepts, for sure!
 
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Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #5 on: April 21, 2022, 09:14:51 pm »
The key to doing the A to D converter is to build a SEQUENCER, as a simple state machine, having a 'test' function, (for analog comparator), where there are 6 simple steps:
   First, everything is cleared, reset, (at step #1).  Then, step #2, will set bit D3, that's the most significant analog value.  For the (optical) comparator, the bit D3 being ON will give the most light, and so is placed closest, to comparing gate.
A 'canceling' step then determines if that (bit3) made an overflow, if so then bit3 is turned back off.
This repeats, for the remaining bits, D2, D1, and D0,
and taking up 2 sequencer steps per bit, 10 steps total, at which time the sequencer sets a status bit 'Conversion Complete', and stops.  Of course, that 'optical' binary encoded result is inverted, but is available, as a 4-bit set of 'light beams', ...(for use in subsequent circuits).
 
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Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #6 on: April 21, 2022, 11:57:59 pm »
...Keep in mind, those 'analog' values are somewhat static, built in by way of input 'weights', where the actual (sourced) original signals are digital.  That attenuation is a bit 'casual'; often done by way of adjusting the distance between sender / receiver.
Also, possible to use partial blocks, for obtaining a set percentage of original, by the time it reaches the 'solar cell' receptor.
   A more fluid example, of analog 'input' light levels, is where the actual electronics portion is modified, such as placing attenuation controls, etc (but can't be PWM control, must be static DC driving the LED intensity).
   But that's THE TELL, in a regular nervous system, some of the 'analog' encoding is hard/ permanent in the synapse structure. I'm not pretending to know, much, neuroscience, but wishing more Neuroscientists would read the EEVBLOG!

   So, the outline, for doing A to D conversion, is, first, creation / design, of a simple light pulse SEQUENCER, (of course with an optical output clock), where the sequencing outputs come from a series of SPDT switches, (all optical), where each individual switch separates out one output, and then goes to 'chain' output mode, for next stage, in the 10 or so stages needed, for the 4-bit analog to digital converter.
   Some of the A/d converter is 'cheating', in a sense, by using wire extended LED 'duplicates', in some cases, rather than a purely optical setup, (that would demand certain mechanical proximity of four different light beams, of the 4 bit weights).
That photo, showing a three input 'gate' helps convey the context, of having all three input drivers at full (digital) output strengths, but then each attenuated according to 'weights' assigned within the structure.
 
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Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #7 on: April 25, 2022, 05:35:53 am »
Photo shows (sorry for blurry vertical axis),  a somewhat close to linear drop-off, in the photovoltaic cell, going from 1 inch to 7 inches apart.  Upper curve is cell open-circuit voltage, typically the circuit switches at around 1.3 volts, in.  That sits well with possible 'NPN' type (input), perhaps with 1 kohm base resistor.
That's going to be, approx. 440 uA (micro-Amps).
That will allow for, along with a 1 kohm resistor, a 0.7 V transistor drop (bipolar).
The lower curve is transistor input current, a bit less, than 'inverse square law', but half's, every 2 1/2 inches
 
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Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #8 on: April 25, 2022, 06:03:45 am »
Hi:
I had been considering, what that little 4 pin (inline) package has inside (?). It controls the battery, solar cell panel and LED output.
But (see prev post), looks a lot like a NPN transistor, a black plastic rectangle, but having 4 leads.
But, along with, apparently digital switching, THERE IS one mode, for having 'analog' on that LED output.
By obtaining negative feedback, by (unusual) way of placing your LED output back against your basic 'input' (Solar Cell), that's feedback by way of the LED intensity, which, BTW seems to stabilize at a rather 'dim' setting, perhaps at something like 80 uA (micro-Amps).
   Otherwise, that LED output is fully ON, at the times when logically that works out (usually, when all inputs are 'dark', or nearly so.(

One current problem is, my 'edge triggering' circuit (made from those yard lights), actually triggers well, and brief, but on BOTH edges, rising and falling edges.
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #9 on: April 25, 2022, 06:14:37 pm »
Here is a view of one particular 'switch', or Optical 'Gate', I like to call it. Takes time, but making secure fixtures eliminates some of the distraction, placing various light-operated pieces in relation.
This piece has only the IC, battery, and LED / reflector, while another table-mount piece contains the little square solar photo-voltaic cell, also glued for upright operation.  All this takes dedication, over stretches of days, so I try to make sure that's worth (the extra trouble).
   Main problem is, there is some mechanism, not a capacitor, but something is creating a delay time...maybe could be the solar cell itself.
(Whenever I try Google 'Solar Panel Impulse Delay Time'...I get some results like:
   'Three months lead time, for Solar Installations, in Midwest...'.
(That's useless).
   But in the edge detect optical circuit, it was supposed to trigger on (just) the falling edge, of light beam input.
So I have to figure out, what's going on with the switching action, as it appears there's a delay, before a new surge of light will create a response, from the circuitry. Since it acts in invert fashion, the newly ON light input causes the circuit to flash it's LED ON.
But if that response is delayed, then my circuit will flash on that (rising) edge, of the input.
 
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Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #10 on: April 25, 2022, 06:15:19 pm »
A better view.
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #11 on: April 27, 2022, 04:58:28 am »
Well I solved a couple pesky problems; the Edge Triggered pulse gen now works: solution involves separating the housing / LED, from solar panel, I'll show that.  Other prob was, how to avoid those, horrible, circular structures, rather than on-line (preferred), again, solved with separated LED, from solar panel.
   On the Edge Trigger circuit (please see picture, of optical gates 'A', 'B', 'C' ), the gate 'B' is separated, that way each part can be put in optimum place.  For the reception, of light from gate 'A', you need the solar panel placement, broadside almost, with gate 'A'.
But then, for pointing (gate 'B') LED, that's a different direction, preferential pointing to gate 'C'.  So that's how you place that LED, so gate 'C' gets the best input.
   You get a nice flash, upon shine your flashlight at start, while avoiding that pulse out, when turning off your flashlight. The 'falling edge' is, more literally, the falling edge, from Gate 'A'.
   So, in this case, it's a falling edge detected, as there is that one logic inverter, first.  At any rate, edge triggered pulses help for conveying overflow from each counter bit (falling edge).

   For the Flip/Flop, a simple, on-line form has two gates, labeled as Q -not, and Q.
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #12 on: April 27, 2022, 05:01:41 am »
This photo shows the on-line Flip-flop circuit, where the first gate is 'Q-not', seen in the left, and is with LED 'ON', meaning illuminated.
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #13 on: April 27, 2022, 05:12:38 am »
This view, the gate on the right is illuminated, being the 'Q' gate output.  That indicates the 2-state thingy is 'SET'.  For doing a SET, or RESET, you simple put a pulse in, into the opposite gate..., so to RESET, you could pulse the 'Q-not' area / solar cell. Actually, literally, that solar cell, is on the 'Q' part of the flip-flop.
(This stuff gets tidious, to get straight, often).
   In the end, you have a beautiful Optically interfaced flip-flop, that gets a light impulse in for the RESET, and another one, to do flip-flop SET.
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #14 on: May 01, 2022, 08:21:22 pm »
Mired in stagnancy / stalemate, that's for sure.
   I've carefully built a couple of separated components; A lamp with reflector that can be positioned independent of main light sensing circuit and battery.
...An upright mounted solar Voltaic cell, on long wires, for the 'bench test rig'.
Plus, a 'Christmas' style LED blinker, for creating repeatable 'Scope traces...
   Now, I can, sort-of, get that goal, of having a full sweep pulse output, detecting a 'falling edge', of a light pulse, but the AMPLITUDE is always low; a dim and very brief light pulse.
It's a lot of 'figiting' and poking at it, as, for one thing, some of those little 'Light Pucks' don't barely emit enough light for causing triggering at the next (component in my edge detect).
   Ever had one of 'those' type stalemate, where everything seems muddied..., and even the failure parts don't express well, or vigorously! (No 'Chi' force, lol).
   At least, I've figured out, the optimum placements, for the 'sensor', vs 'output' (LED), are located in completely different places, relative to other components.
That's why I had to split up one of the yard lights, in the first place.
...more later, thanks.
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #15 on: May 02, 2022, 01:11:43 am »
To show what I mean, by 'flakey' results...Even some of the 'failure modes', are flakey...like, for example, my trial edge detect circuit, currently exhibits a pulse output on BOTH edges, rising and falling.
..intermittently.
(See photo) That photocell 'splitter' allows for 2 inputs, while blocking any light leakage.  The items feeding the top half must not get any light, from the lower light output feed: that's why you can see the divider going across the cell (#3).
That (friggin) divider, had to push and pull that, just for having both light inputs be enough to trigger the #3 unit.  As in the classic edge detect, the upper signal (signals going left to right), the upper signal is the straight input, although inverted by gate unit #1.
The other half, is sent by way of gate #2, the solar sensor being #2A, there.  The purpose, via gate #2, is to provide a (very short) delay, before the delayed signal causes gate #3 inhibit (lower signal path).
This is all very solid, in theory. However, first of all, any light that leaks, forward through the logic, can cause a 'linear mode', where you have negative feedback, thru the solar voltaic cell, in the loop. That exhibits as a very dim lit LED...I'm not yet sure if that's oscillating, depending on phase, around 180 degrees, and other factors, as I'm not familiar with the 4 pin IC controller (inside each yard light).
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #16 on: May 02, 2022, 01:12:47 am »
...here is view, of that separation wall, for the solar cell.
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #17 on: May 02, 2022, 01:28:52 am »
Sorry, if the presentation is cryptic: those rectangles in the last 2 pictures, represent each individually operating solar light, with gate #1 being the input. Now, the circuit is called a falling edge detect, but input is buffered, so that, logically, the whole module acts on the RISING EDGE, of your ultimate input.
The gate #2 performs the logical AND using low going signals, so literally it's a NOR gate.  It's just that it's used (Thevinin Equiv.) so it needs both inputs low, to deliver the pulse (-P type) output, from gate #3.
For an NPN transistor, like a 2n2222, I could expect, maybe 100 nano seconds switching time.  There aren't any capacitors visible, inside the little lawn lights.
That means to expect, current delivered to LED output, will be interrupted soon after the #2 solar cell stops issue voltage. (That's why considered as an inverter).

   The two extra lawn lights, are options placed into the gate #2 path, in attempts to cause an increase, in the blink time, of the pulsed output.
Driving the input of unit #1, is a typical flashing LED.
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #18 on: May 04, 2022, 07:03:22 pm »
      On The Optical Circuits, Generally:
   Progress on some details, of the bi-stable bit latch, and on the pulse edge-detect dynamics.
A few more sketches on that Analog to Digital layout scheme, a favored aspect because of the somewhat close analogy with neurons (...if I got that right, lol).

   Due to the output weakness of LED light, for causing triggering, one method helps; by splitting a signal into 2 separate copies.  That way, no worries, about 'sharing' some output light, between a couple of different receiver (cells).
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #19 on: May 04, 2022, 07:28:11 pm »
Plus, adding to all this, those little Solar Light's LED for output, often are pointed, grossly, off somewhere very off-center, and the ones I'm testing generally use LED lense/housing. I estimated, those LED directionality is to take up approx 50 ° (degrees) horiz; and 50 ° degrees vertical, for about 1/25th of a full sphere.  So that comes to, estimated, a X 25 factor and a ÷ by 27 factor, for geometric 'R cubed'. That starts to fit my results, where the solar cell response has voltage dropping off, a bit slower than some 'R squared', but it's close to R squared.
   I find it a bit interesting, (and vexxing): here we have that large Solar Voltaic cell surface, ...acting like a summing node, in analog circuitry.
But yet, the LEDs 'sending' portion has those flakey directionality flaws, or at least inconsistencies.
   A newly built test lamp, has surface mounted 'green dot' LED emitters, already precisely positioned in reflector, so that's nice. 
Another variable in this process is the Solar Cell efficiency, relative to all these various LED emission color options.
(Those newly built lamps, are obtained by salvaging parts out of DOLLAR STORE flashlights, on sale).
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #20 on: May 04, 2022, 08:11:54 pm »
This photo shows: I'm having troubles, getting the screw terminal blocks to work, decent, with the delicate wires, often part of a separated, Solar Cell and nearby LED decorative light.
Problem with screw terminal block is the GAUGE; that light gauge wire does not 'squeeze' securely, underneath terminal, and, worse, those screw-down terminals can actually crush / break any soldered or tinned wire lead ends.
Best I'm going for now, is to solder a short (1 inch) piece of heavier solid wire, for direct insert into a regular IC solderless breadboard.
 

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #21 on: May 04, 2022, 08:17:13 pm »
Here is photo of some of the separated LED lamps, each with a fairly long lead set, for connection at that solderless breadboard or with a set of screw terminals.
By the way, using only one battery cell, at 1.3 V there is no external LED resistor, so any (future) testing that involves higher supply voltages (5V, or even 12 V), requires some resistor (range 220 ohms up to 1 k or so.)
 
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Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #22 on: May 04, 2022, 11:40:45 pm »
It's the analog aspects, of the Solar Light switching that is interesting.  That's why an example, Analog to Digital conversion, helps show the digital sequencing along with the analog response, and how they relate.
The scheme differs slightly, from conventional AtoD subsystems.
   Firstly, not much hope of going beyond about 4 bits of resolution just simply for mechanical reasons, too many components, in small spaces
Example includes a 3-bit layout, with maximum A/D count of '8'.  Each bit will contribute according to binary weight.  Now, it took a lot of thought, but I've set the A/D system up for 1 count = 200 mVolts.
The 'overflow' value used is '7', a little unusual, but at that scale, a resultant A to D voltage reading is 1.4 volts.  Readers may recall, the value, near 1.35 volts is where device switching occurs.
Conventionally, a different choice would have been, to use overflow (to '8', a binary boundary), and to assign each count as 160 mV each.
   The rationale for using '7', instead, for the overflow, has to do with so-called 'Two's Complement' representation:. Consider, an ambient (light) condition causing something around a quarter of total light, from natural and from (yard light LED) sources:
So, an ambient level, at count of 2, would require the REFERENCE Digital to Analog source to count up, reaching overflow status at count = 5.
Notice, that '5' is directly a complement, of value under measurement: level of '2'.  Otherwise, with more conventional overflow, at '8', will produce a result,..
.I.E. '6'; which would require 'Two's complement' additional process, so total process, for an AtoD answer would then require COMPLEMENT (easy), and then an INCREMENT (slightly tough, using all optical register logic).
   At any rate, the explanation is unconventional, but is mere conjecture anyway: The little light simply switches, nominal, near 1.35 volts, 1.40 volts being 'nicely' represented, by AtoD count of '7'.
   The other unconventional aspect, is that there are TWO analog sources, between the ambient light (about 2 out of the 7 total counts, and the Digital to Analog source, giving out '5' counts worth of light (that would be 5 X 200mV = 1.0 volts. ). Adding then, the ambient contribution, of 2 X 200mV and you reach the trigger level, of 1.4 Volts.
   There was concern, initially, that some A to D full counts are not there, thus some loss of already low, resolution.  However, when asked, to regurgitate an analog value, a Digital to Analog converter WILL produce, normally, all amplitude counts, 0 thru 7, even though original converter only utilized, up to count of five.  All this is normal, as also, when ambient light factor is 'zero', the system has to count up to '7', then invert, to show a correct value, (of 000 binary).
So you have full range and resolution, (within that, crappy counts 0 through 7 range), it's just that most Analog to Digital conversions only involve one single parameter, not two, that have been summed.

   It seemed perplexing for a second, as I contemplated, how to construct that Optical Logic A to D converter, how to bring analog values in, for summing (at the photo cell).  But THEN realirzed, NO, those signals are still digital (meaning rail to rail voltage swing), with analog process only at the destination; the analog weights tweaked by filters, reducing intensity, so that bit 2, for example, the MSB, is done with a '50%' blocking or partially obscure filter. That would be placed in front of the LED emitter for bit2.
Of course, distance to the 'comparator' gate is another potential manipulation method...having nothing to do with the very very very slight increased (light) propagation time, a couple extra inches...that's negligible.
   So there you have it: An intro to a digital gate system, having analog qualities, briefly or in one specific region (near to the switching input).
Reading, in biosciences book 'NeuroScience for Dummie', this is almost exactly similar to neurons, except one (interesting) aspect:
   Neurons do their job, having, sometimes HUNDREDs of little digital inputs (synapses).
I can't solder that fast, but interesting results to be had,
(If I can wrestle out all these variables.)

   "N cans, holding 'N' worms..."

--Rick B.

 
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Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #23 on: May 06, 2022, 10:15:01 am »
More 'figiting and fussing'...  (Trials, for doing a pulse logic generator).
The incoming light (see photo, left side), goes through the series, along bottom, while also having a signal path, along the top; each signal path ending up as the inputs, to the final 'gate' (that's short-term for each separate 'lawn light').
Each separate experimental layout needs special attention, as the individual lights (Dollar Store discounted) are of limited quality, as in battery charge duration, LED pointing mis-align (path to next unit, for the feebled output), and potential for 'leakage', random,from one unit to (some) other, in the optical logic circuit.
   YUP; NOPE, this set-up does not even barely work, looking to see an output 'flash', as the inverting logic, of each gate, should create a 'rising edge' responding situation. 
   Also, the cheaper Solar Lights seem to have pretty marginal (AAA battery) running time, each evening.
The light's internal switching is done by way of a 4 pin IC, some are calling that a 'Buck Converter'...but I don't see any inductor, ...or capacitor, in the little circuits.
Found some other bloggers postings, for Yard Lights projects:. Big Clive.com has materials and actually does great job, very clear diagrams...(I should learn something, there).
Others do 'Art Projects', involving individual yard lights.  But I'm interested in the switching behavior (with analog parameters, as I've said).
   In my diagram, the upper signal path is the 'delay' line, operating a 'NOR' gate, essentially, along with the lower signal path.  Briefly, the final gate (on the right), will pulse, during the very brief interval, before the upper signal 'catches up', and supplies an 'inhibit' signal.  In theory, but it's not working. (Output stays blank).  I had been planning to attach Oscilloscope, to measure output pulse duration.
   I did realize, only recent, that the (single mh cell) likely is seen as a (large) capacitance, by the switching IC 'Buck Voltage circuit'...
   While viewing the diagram, it helps to view each 'gate', as a logical inverter, so the upper signal path (green units), is producing an inverted outcome, vs the lower signal path, which inverts twice and thus maintaining the original input state (coming off the very first buffer).
 

Offline RJHayward

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Re: Optical Bench REDUX: Digital Switching can have Analog Functions!
« Reply #24 on: May 06, 2022, 10:17:30 pm »
More filling in the question areas, on the switching characteristics of those Solar Yard lights.
   Photo shows the little PC board, no caps or inductors; just a single resistor, for the LED output current limiting.  The 4-pin switcher, (sometimes called buck converter), is a bit small, there next to the yellow wire and white wire.  Several unfilled PADs seem to imply that manufacture had other options.  This is a step up in quality, over some Dollar Store lights, so perhaps the units sold had been 'downgraded', by process of eliminating (any) possible components, especially a coil for 'bucking' a higher LED drive voltage, than the 1.3 V nominal nicad battery (in other more expensive lights).
   Also, before I forget, a strange use was made, utilizing the SWITCH HOUSING solder terminals as a conductor, (if I'm to believe my eyes).  Only guess I can make, is that there might be other models of garden light, that leave out that on-off switch, while perhaps populating other PC board 'missing' items, L1 coil, and C1 capacitor.  The battery, being a nice (nicad) AA type
holds more promising run time, at night before it drains down.
   But, for the purposes of THIS light assembly the components seem to be bare minimum, for lower price points, and satisfying a growing consumer acceptance.  Ten years ago it was different: the batteries were all AA, and typical units had a centralized driver / Solar Panel, with LED power leads going out to each individual.
Also, earlier units used a CDS device (that's Cadmium Sulfide light dependant resistor).  Funny, those Cds light sensors sat right next to any solar power cell...
I wonder, if there was an 'AH HA' moment ?
(Being that a 'Solar Cell' actually IS a potential sensor.)
   That on-off switch looks like has an option, when in the OFF position, of a second resistor, R2, for trickle charge, even when Yard Light LED is shut off.  So, yes, money was saved, by leaving out the option, for charging (the customer's) battery, even when LED was switched off.  In this Dollar Store thrift version, that penny savings, at the factor, was a GREED option..., perhaps, and in 'the dark' (yeah, a Pun), for any customers, myself included.
There's a couple of other 'short-cuts' seen in some cheap units, such as glueing or even soldering that battery in place.
   But back to my project needs: I've figured out, the LED is essentially switched to ground, on the negative LED terminal, very similar to typical low-going NPN transistor switches.
But I bet...if done over, 2012 thru to now, that particular model would eliminate the switch, and go to AAA batt sizing...just to get into that Dirt Cheap / discounted product.
Nothing wrong with, some, of that 'quality down-grade', as I've heard of older landscape lighting (low Voltage AC) costing upwards of $100 per garden light!
The inductor, in this current style, probably allows for bigger, multi-LED units, while also perhaps a capacitor helped, in some situations, for avoiding flicker, in some situations ...(??)
 
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