Photoelectric light controls are weirder than they seem
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- čas přidán 25. 08. 2023
- I had no idea that's what's going on inside.
Technology Connextras (my second channel where stuff goes sometimes)
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I don't know what kind of magic Alec uses, but the fact that he releases videos on topics that I really couldn't care less about, and that I watch them, is a testament to something I suppose. He finds a way to make things that are rather irrelevant to me interesting, and I rarely pass up the opportunity to watch a Technology Connections video.
Usually the magic of buying two
@drumset09 Somewhere there is a streetlight that is oddly missing a sensor and a bulb.
@TonyP0927 It's probably the one at the end of my street that hasn't worked right since I moved in and all calls to the city have gone unanswered...
His videos are curiously entertaining and educational. His voice is generally calming. And the detail he gives during explanations are usually so good that I can visualize what’s happening even though my eyes are closed and I’m using the video as a bedtime story 👍🏽😉
There is even more edu-tainment if you actually *watch* the video. Especially if watching with captions. 😊
anything is interesting if the presenter is interested. That’s what I think :)
Always a joy. After a 45+ year career in IT, I love how you elegantly summarized the challenges of software in a few seconds. Spot on, LOL
The software issue was amazing hahahhahahhaa
undoubtedly a dig at adobe premiere 😆
@blaknoizee A picture is worth a thousand words.
To be fair, the software required to control this particular application would be very simple and easy to verify correctness / test. But as others have said, a microcontroller-based solution would suffer from other issues which this design avoids entirely, and the circuit design would need to be proportionally more complex/expensive to compensate. If it ain't broke, don't fix it.
@Michael Calvin new installations are micro-controller based and this allows for load shedding and features like turning every other light off after midnight, dimming and other such features. They can even tell if any have failed and wait until that meets a threshold before they send a man with a pole out to smack it. I would imagine such features would be mandatory if they are not already especially in the EU. North America tends no to bother with that nonsense (for now). You don't need to worry too much about the MCU having issues because the LED fixtures fail much well before!
We had a little craze here in Brazil in the late 90's, where kids would use laser pointers to turn off streetlights. Sometimes a single lamp would turn off, other times a whole block or more would go dark. Good times.
that sounds like something i should try. but then again...i have a key to open the street lamps and could just turn them off forever. :D
While I don't approve of this, it is ingenious!
@MoosWhere I live there is a side road with the new led illumination and someone rotated the streetlight to use it as a free illumination for his garden, where originally was illuminating a corner with a wall.
Not even a week after, a car slammed on the wall that was now in complete darkness.
As a kid, I discovered that if I took a small mirror and held it up against a light-sensing nightlight, angling it so that the light from the bulb would be reflected to the photoresistor, the nightlight would go into a feedback loop and start flickering like a strobe light.
I ended up with an outdoor light that did similar. I installed a screw-win dusk to dawn sensor in the lamp. The photoresistor was catching a reflection off the shiny lamp housing and was causing the light to cycle on and off
Obviously it had no hysteresis built in.😎
That's how Disco lights were Disco-vered. ;D
I was able to do that with just my hand, it was fun.
Laser too
While explaining how the mechanism delays turning on the street light, I'm sitting here thinking "This is a really clever hysteresis. I really hope he explains that it is"
"Some people would like me to say the word 'hysteresis'. You're welcome!" - I've never felt so cared for and shouted out before
I work at a hardware store. This video has taught me how one of the products we sell works. This isn't the first time you've done so, but it's the most direct time you've done so and I want you to know I appreciate it. Your videos on regular switches and thermostats and LED bulbs are probably more important, but this one is illuminating in a way I had no idea it could be.
Illuminating, you say...
Here in UK, when I was young in the ('50s and early '60s) street lights had simple timer switches, not controllable over the supply. I discovered that the ring magnets from old B&W TV sets could be used to switch the lights on or off by swiping the magnet across the metal access panel. What really happened is that the switch phase was changed, so when the light should be off it was on, and vice versa, and it required a visit from a person to reset the phase.
anarchy in the UK
@Dan B It was scientific experimentation. Honest!
Back in the 70s as a kid I 'err, rescued' one 'hanging out of a lamppost' and used it to switch the Xmas lights on and off. Turns out they are quite sophisticated and can automatically adjust for BST and the sunset / sunrise time.
Some still use timers, not so simple ones though :D. For example the lights here go out again about 1am for the remainder of the night.
@Ewan Marshall The timers were usually set to switch off at 10:30 in Leeds, after which time it was pitch black.
It's back!! The painfully smooth jazz, the patrons, bloopers, funny closed captioning joke at the end. I live for that at the end. My boyfriend introduced me to your channel a couple of years ago, and when you have a new episode, we get excited and wait until we are together to watch it like a little date. He's a mechanical engineer, and I'm just a lady who enjoys good puns and having my mind blown by things I never knew. I really enjoyed the toaster episode.
aw thats adorable, hope things always go that well for y'all
What's even more crazy to me is that he doesn't even have any formal engineering background, it's all self taught!
In the 80's we only had a single one of those at a central junction box, controlling all the street lights for miles around. We kids back then would sneak there in the dark, climb up and put a flashlight over it. This was particularly fun during the dark fall and winter season, of course. Thinking back it seems strange how this sensor was not covered in disabling snow and ice, but maybe the heat from that thermo switch was less of a quirk and more of a critical feature...
I am one of the hysteresis people! I feel so seen and I think you do a great job dealing with us pedants. Actually you even got praise from my favorite youtuber this month acollierastro about how well you explain stuff so everyone is satisfied a couple months ago in her video on Gell-Mann Amnesia. Highly recommended!
This might be the most in-depth electronics-focused video I've seen from him, and it's very well-produced. Several times I thought "I'mma leave a comment if-" and then he immediately quashed my urge. Strong evidence of good research and planning. Never change, Alec!
Alec, I've been watching your videos for years now and they've only gotten better. I'm wondering though, why no video on the central vacuum? I feel like it'd fit your channel perfectly and it's definitely an interesting topic, considering how nearly every home at one point was retrofitted for one and yet it died out so fast.
I worked at GE for Lightgrid V2, that was funny to see something I know so well on this channel (amazing work btw!). I just wanted to add: they definetly do put microcontrollers in those, the nodes (the thing with the three prongs) linked together and form a mesh network to send data on usage and breakages, it's actually a really neat idea, and was really useful to facilitate negotiations for power bills of big cities. But sometimes you can't outsmart simple: the city of Montreal (who was our big customer at the time) had all its light fixtures on a timer circuit, by the time the microcontroller was all up and running and the network reformed it was daylight and everything was shutting down again. In the end the data was still gathered and the system was useful, but looking back the timer was probably doing most of the actual work haha
17:15 This device is much more tolerant to lightning, too. Important when it's setting atop a tall, grounded metal spike.
I mean if that is a worry, give it a Faraday cage, problem solved
I doubt it would survive a lightning strike. Even if it did, plenty else in the street lamp wouldn't. Including the lamp itself.
Source?
@Lilly P that ads more cost, complexity, and points of failure. It can be easy to solve a lot of the problems that can arise when engineering something, but its very difficult to do it in a simple, cost effective manner that increases longevity. there is a reason why "over engineered" is a common phrase.
Funny you should say that. The last time I saw the insides of one of these controllers was when it had just been turned into plasma by a lightning strike. I was stopped at a red light and was across the street at the time, about 50 feet away.
That's quite an amazing way of doing it tbh. I assumed they would've used a standard circuit using a comparator etc but it's quite ingenious done with a thermal switch and resistors acting as a heater. I literally lol'd when you said hysteresis because I was thinking exactly that. I enjoy nerding out on your channel :)
My favorite photoresistor nightlights are a couple of LED units which happen to dim the led smoothly as the light increases. This means you can control the brightness by how far away your hand is from the sensor. It’s not better than a simple on/off, but it is more fun. 😀
Absolutely love the bimetallic modules for a couple of a reasons; 1) for a simple automated switch they can handle HUGE continuous loads relative to their size (rated 1800w but in reality can handle up to 2300 safely for years and years) 2) high reliability and 3) they fail in the 'on' position which is super important for apartment & security lighting. They really were and still are an elegant solution
I enjoy your videos. Interesting information that often takes something I knew about - but afterwards I know more about. Just enough cheesy humor to be fun but not annoying. No annoying looping music track playing over top of your speech. Calm, good video editing without adding a bunch of annoying 'busy' effects the way some youtubers do to make their videos more 'interesting'. Keep up the good work. :)
This guy has figured out the secret to having a successful channel without putting up an obnoxious Subscribe/bell button animation every three minutes. Turns out the trick is quality. Who knew?
Yet again as a software developer I’m impressed that electrical engineers come up with some odd ball solutions to make things work
The little bit of heat they create probably helps melt snow off them in the winter, keeping the light from being on all the time because the sensor is covered up. Like how stoplights had to add heaters when the went to LEDs.
*_BUT SOMETIMES!_*
Although don't traffic light heaters only operate when it is snowing and thus still end up using less power than incandescent?
@soundsparkEven when heating the snow away it probably uses the same if not less power.
Or we have heaters as option to more efficient ones to turn on during snowy days, and you can control it with a tiny LED and a fibre optic, if snow can reflect the light to a light sensor, heater go on, no snow, light isn't reflected, no heater
@Lilly PNo need for even that much complexity. There are transistor output thermal sensors packaged in TO-92 that come with factory calibrated thresholds that can serve the same role as the LDR, but for temperature. This would just kick a heater on when the temperature goes low enough, which would obviously be a bit less efficient than controls that need actual snow to activate, but it would work and it would bypass the need for fiddly fiber optics, the chance of unskilled assemblers screwing up placement and alignment, the addition components to read and react to the level of reflected light, and the need for the clever physical engineering required to make sure that snow falling with any vecor activates the sensor.
Here in Brazil these sensors are completely diferrent! they use a Whetstone Bridge to click a relay, they even have a trimpot sometimes to regulate the amount of light it will turn on or off. I think its a better design because it don't get efected by the temperature of the place, they are a little bit smaller too.
My dad installed streetlights as a side job for years and would bring me to help. I remember installing quite a few of those light sensors (the cities did 1 per light pole) and even needing to take down a few poles because I forgot to put it in.
It's cool to see how those little boxes actually work.
I have a pretty solid understanding of electronics and controllers(do a lot of hvac work) and I find the breakdowns on some of these oddball topics MASSIVELY useful. I am not a lineman or a dishwasher repairman, so being able to see inside of some of this stuff has helped me work on my own stuff because they end up using the same types of controls and components across a boatload of industries. There's so many appliances I look at now and have an idea of what I'm getting myself into before tinkering around trying to fix them, because of this channel. I don't think I've gotten bad input from a single one of these videos(even when corrections happened for some) because there's such a no-nonsense approach to how and why something does what it does.
As someone who knows nothing about electronics, I’m curious: if the light sensor activates during the day, what stops us from just using a NOT gate to flip the output?
@Colin Hulme Pretty sure he covered that. I assume the NOT gate is provided via a plc or something capable of flipping bits on and off in your question-
It's because a plc or controller that's similar have many more failure points inherent to their build/design. Each additional wire, chip, board, connector, etc is another way the control circuit can fail on something like this.
In the lamp and controls being discussed, this is already a mechanically applied NOT gate - you can view the temperature as the i/o. Above X degrees = 0, below X degrees = 1.
If you're a programmer looking to learn a bit more I'd suggest looking up ladder logic and plc programming guides. Lots of free resources and tools that show you how to approach electricity. Flip switches for your lights are just mechanical i/o. If 'yes', light=on. For something like your dishwasher it'll check temps, open valves, close valves check water levels, release soap dispensers, etc with pretty much all mechanical inputs that work based on ladder logic, ladder logic just being another form of truth tables
Thanks @Terro Viscenscity !
This felt like a real old school video, just interesting information delivered in an enjoyable way
I'm finishing my undergrad EE course some time soon and I always liked the relaxed and fun way you conduct your videos. I can't recall you presenting electronic schematics in your older videos and it caught my attention! I truly believe you're helping to encourage some young folks into this wonderful world of electronic engineering (as well as other engineering areas) through tinkering with some basic problem-solving-devices. Nice!
Before you finished there are two critical things to do. Have an internship and take the FE exam. This will help so much in getting your first job. It is much harder than expected. I’ve been there.
Yet again, you’ve used your technological powers to shine light on an interesting subject. Thank you for your illuminating video. You’ve brightened my day.
Pack it in, everyone. Nobody's gonna top that.
These puns are too hot. I'm gonna have to wait for nightfall for things to cool down.
arghhh so much pun, i cant handle it
You are under arrest for pun crimes!
Yeah, I can never resist these videos. Any reluctance I have towards watching 20 minute videos just switches off.
This is super interesting to me knowing every one of the street lights down my street come on at random times from one another. I thought they where on timers for the longest time and where just out of sync but I guess they all have their own photo sensor lol
Another home run, Alec!!! Great vid. Love the thermal imaging. And as always I love your set. Lava lamps 7x was fun haha
I wired the black box style into my porch lights on my house. Cool to see how they achieved the delay to prevent rapid on/off conditions. I've never noticed the lights coming on immediately after a power outage (because that's never a point where I'm paying much attention to my porch lights), but I'll definitely be looking for that next time it happens.
Your videos are getting better and better! And they were pretty good to begin with. Personally, I find the low-key humor highly entertaining, and having the captions on makes it all even better!
There's a third option aside from thermo-mechanical and software: I used to control my garden lights, which ran off 12V DC, using a switch I threw together myself. You can do hysteresis purely in analog electronics. It requires a bog-standard comparator (I used the good old 741) and a couple of resistors.
I've been watching your content for at least a year, and became an electrician along the way. I'm thrilled that your content is not only still amusing, but actually useful to my work. Cheers, and thanks for making it
This was a great example of a simple thyristor switch in a real world application. They also have large ones which can handle much higher power loads, but I guess a limit switch will do just fine.
I'm also an electrician and these videos helped me a lot during my apprenticeship. I'm confident with maths and logic but I struggle with concepts, his videos on switches and all types of electrical components really helped me grasp what was going on. Hell, I'm qualified now and even this video taught me something, I put in sunset switches pretty regularly and I've never thought to look into how they work
I was looking into buying a switch like this for a bit, but this video showed me I can just use the photo resistor directly. I wanted to implement a daylight sensor in a car, and I'm already using a raspberry pi of sorts to control a bunch of junk, so I'm glad this could help me save a bit of money and complexity
Credit where credit is due. I would have to say that over the years your clarity has increased tenfold. Really excellent presentation of whatever technology you are explaining. I like the fact that you use the word contactor instead of relay as well. Nice attention to detail. You might have explained that contactor is really just a form of a high current relay with good longevity, but now I am nitpicking. Keep up the good work!
I never get tired of seeing engineering that works through clever application of technology we've had for generations instead of just checking a digital lookup table in some firmware.
18:25 I know you have a great handle on things when it comes to filming, but if you want to save a little time on redoing takes because something hit the table you could put some wide loop tape (soft side of velcro) along the back side and bottom edge of your table, that way even if you bump something into it the audio won't be messed up.
It's crazy how timely this is for me, as I'm looking into some streetlamp-based RF networking gear - one of the limitations of which, is needing the lamps that have a photo detector at each pole... And now I know why - it's required to ensure the networking components can stay on all day.
When I was working as an electrician and was keeping street lights in shape, I was quite often dealing with those sensors. And contactors they control. We used to call those photo resistors as "the eyes". It's quite the feel when you cover those and you hear that loud *clack*
If you happen to be working inside one of them when you hear the click I would probably ruin my white pants
@Maddie well, you'd be too far in such a case to hear that clack
The beauty of this simple photo switch is in the "eye" of the beholder. ;)
That loud clack, for me was in a cabinet of many contactors. You want scary, try a liquid resistor starter. ( motor starters ). 3 tanks of "dirty water", looks like big batteries, that when that first loud clack happens, it is completely drowned out by the electric arc sound from those tanks complete with bright flashing lights. When the 2nd stage kicks in it goes quiet but those tanks are still connected to the power, don't drop your spanner etc, they will bite.
This has answered so many random questions I had about street lamps and light controls that I never consciously knew I had!
Many decades ago (late 70's) those streelight controls did use thyristors and relays to do the switching. And yes, they were very prone to short cycling from lightning and sometimes even bright headlights.
There are definitely some thyristor-based streetlight controllers on the market, I have taken a few apart.
Another interesting tidbit - at one stage in the UK, streetlights were controlled by pulses put onto the mains waveforms. Early switchmode power supply’s were sometimes known to put so much noise back into the mains that they would activate nearby streetlights when used.
I think the technique you're referring to is "ripple control". To this day it is in use in the Netherlands to switch street lights, but it is being phased out. Tariff switching of meters using ripple control has stopped in 2021.
A lot of LED lighting equipment is rather sensitive to this ripple control signal leading to complaints of flickering lights at certain times of the day. Added to that it's an expensive and obsolete technology.
This was actually super cool to see, it's probably the last thing I'd think of, but also one of the simplest. I would like to see other designs, I live in the UK and the lamppost outside my house turns on and off for 10 or so minutes while there's just barely enough light to make it think it's getting dark, and obviously that is quite a different design. I also think they are newer maybe LED lights or at least not sodium, so that probably has an effect.
I was surprised that the photoresistor in street lamps did not directly control the lights but actually controlled the heating element. But preventing erratic on/off of the lights does make sense. Thanks again for the info.
I never knew how simple these devices are but just how well they do their job. This is one of my favorite educational channels.
Remember that simple in execution doesn't always mean simple in design/creation/implementation.
There are plenty of "simple" things that we don't realize we can apply to solve complicated problems for a LONG time, because it takes a through understanding of something, plus a bit of creativity, to apply it.
Take the FFT. It's not doing anything 'new'. But realizing we could use it to VASTLY simplify some things was evolutionary.
@OverwatchIf an FFT isn't doing anything new, then there truly is nothing new under the sun.
And most of the time, they do their job so well that you don’t even realize how well they do it.
Right? Seems like something that should be taught in high school. It amazes me how so many useful things can be done by pushing electrons around.
So simple. Yet so clever. I had no idea this was how they worked, but I like it. Thanks for showing us inside.
Long time fan here, just to say that I had no idea how much more enjoyable this videos were when going to sleep after a night out.
I was like "aight, now the party starts"
You just gave me a supplementary lesson in electronics, which I could have gotten in EE vocational high school but I was too busy plaiyng doom and listening to Cypress Hill... thanks! It clicked. e: figuring out to hack a gate based on the thing resistors actually do is... so brilliant it's insane, and makes for a video that stands as a perfect example of what you do :P
Awesome description as always. Another interesting side effect of how these work is if there is a poor connection on the power, usually a bad neutral, the sodium vapor lamp will get stuck ON in the day time.
Photoresistors were used in the classic 60's guitar chorus pedal the 'Univibe' and is partly what gives it its' unique character :)
Another common method you will see in devices such as those battery powered yard LED lights with solar cells, is the same cell that is used to power the battery during the day, is then used as a switch to enable the LED during night.
This is becoming very common in Australia (at least the parts I live) with basically every new street light now being LED. I assume they have electronics to control the on/off state. Yo usee both hardwired versions but also battery "off grid" versions.
Then again once you leave the cities the *whole country* is off grid.
I wonder if those thermostatic switches activate at an absolute temperature or a temperature differential. The latter would make them more consistent between winter and summer.
This has to be my favorite episode! So simple, yet so informative!
Way simpler than a uController and maybe more robust than mechanical parts, you could have something like a TRIAC driving the lamp with ceramic caps to create an hysteresis.
Anyway, love your channel! Always happy when I see a new one popup in my feed!
I have had the chance to take a couple of these apart through the years, and there have been a few different versions based on what was cheapest. I have seen a version that used a few resistors and a relay and I have seen a version that used a triac and relay (in addition to the light dependent resistor).
The turning on after a power outage sounds like a good feature - means if power comes on during a night failure it will immediately be illuminating the streets instead of a warm up delay.
Also the temp higher to turn off would probably be helped by the sunlight on the enclosure warming it during the day.
Yes please! Would love more, essentially "electrical engineering 101 classes" from you :D. I did a unit of electronics stuff for my networking uni degree but didn't really ever understand it and never ended up pursuing that path so it's nice to learn this stuff from someone who values entertainment over passing dry test materials hah
You might want to watch some of Big Clive's videos. He does a lot of reverse-engineering of consumer electronics and is pretty entertaining to boot.
@Matthew GiesClive is a legend
@Matthew Gies Is that the one that drinks while he's doing teardowns? There's a guy on CZcams that drinks and gets stuff wrong a lot - not sure you should be learning from that one 😅
@3nertia I've never seen a beverage during a teardown. He does use a SodaStream to carbonate random alcoholic beverages, though, in a very different genre of video he also does.
@Matthew Gies Yes, it was my mistake. I was thinking of pileofstuff! Apologies! I watch a lot of these sorts of channels and they tend to get all jumbled together in my head sometimes 😅
I have been seeing on my dash, clips from TikTok of lightbulbs with some kind of metal flowers in them. The flowers look like solid metal, not like the shaped filaments you've done before. They light up colors and look pretty cool. I'd love to hear how they work or if they are even real.
Really interesting video. In Europe we're gradually replacing sodium lamps with LEDs - better longevity, more useful light and also cheaper to operate. The operational advantage is that they're connected via cellular low-power WAN, so it becomes possible to provide fine control of their operation as well as generate notifications of malfunctioning infrastructure.
Awesome. I have used these for exterior lights in the past, nice to see how they work.
Alec, I can sense your concerted (and hugely appreciated) effort to suppress “comedic” injection into the dialogue. It never worked well for me, and I initially subscribed to your channel because of the low distraction, calm and rational analysis of subject matter.
I cannot tell you how much I, and I’m sure many others too, appreciate your reversion to “the old Alec” who didn’t feel the urge to transform a basic technical document into a comedy routine.
Thank you, with utter sincerity. ❤
Love your videos Alex. I hope the joy they bring me continues coming for many more years!
The brief turning on of streetlights after a power outage was a real thing. I used to see streetlights go on for a few minutes after a power off as a kid and wondering what is wrong with the lighting system. There wasn't anything wrong. It was just an artifact. 😐
Though I suppose it could be useful, too, to verify that, yes, all the lights are working. 💡
One problem with this artifact is that after a massive blackout, when one need to restart the network, any extra consumer that turns back on makes the process more difficult. So in case of several cities having to be reconnected, all those lights will actually be part of the problem
@AaronOfMpls It's not a bug, it's a feature.
@AaronOfMpls just like when you start a car and all the dashboard lights come on for a second, so you know they are in fact working.
I’ve always wondered how photo electric cells work. Thank you very much for this video.
I remember building something like this in secondary school over 20 years ago.
was an LDR, transistor, a few extra resistors, a diode and relay.
Alec, you're the best! Love your videos and sense of humour, please keep making them!
Great video as always!! I would assume that the built-in heating has the added benefit of preventing the photo-resistor from being obstructed by a build-up of snow and ice? So in colder climates, a more energy-efficient sensor might require a heating element anyway, or regular manual de-frosting. Especially if the module isn't mounted directly in top of the light it controls - in which case the an daytime activation of the bulb might produce enough heat to clear the view for the photoresistor, turning the power off again.
interestingly, my town had switched to LED streetlamps in some spots and I've sometimes seen them flashing periodically at sunset, so they must have been using some other kind of switch.
Lots of cities in Germany use a mechanism called ripple control to turn street lights on and off. Control messages are sent by the grid operator by modulating the line voltage (from what I have read), so there is no need for extra communication lines or radio. It's essentially a very low bandwidth form of the power-line communication that's available in consumer products.
12:19 Thank you!
also as an electrical engineer by training I figured on the solution for hysteresis being some kind of op-amp integrator, this solution is so much cleaner (not least because you don't need rectification or voltage conversion), and as soon as you said thermostat at the beginning I went "Oh that's so smart!"
I wasn't expecting a thermal switch because the one I have of the same type contains a relay instead, also an even larger photo cell.
Your videos are so fun and unique, so interesting, well-structured, researched, and produced. Always a pleasure to find a new video in my feed.
In my experience, our street lighting is controlled by a timer, carefully calibrated in such a way that it's still pitch dark when it turns lights off in the "morning".
This was way more interesting than it had any right to be. Well done! Plus, I learned a new word: hysteresis. 😊
When you mentioned Thyristors it brought to mind the classic “Automatic” camera flashes controlled by them. I know you’ve covered film photography before, perhaps you could do a dive into flash photography and the various ways it’s been achieved and controlled. I think that would be quite interesting especially with your presentation style.
The magic of the "thyristor" flash units was that they didn't waster power. Before that design, a flash unit would take a long time to charge and use all of the power to flash, even when only a short (dim) flash was necessary.
With the thyristors, the flash only put out the necessary amount of light, so often only a very short recharge time was required before the next flash could be produced.
It depends on where these are mounted, that heater may have use. When snow falls, it falls on everything, so the heater may be getting rid of a snow load on it. Also where it snows, we sometimes get freezing rain and sleet, which would block the eye of the thing
I often work with photocells, but never would have guessed that this is how they work. I never took one apart to figure it out...
I had designed LDR controlled lights before, but using semiconductor. I have learnt something new about the use of bimetallic switch in street light control devices today. Thank you.
Great video, as always! I never expected that, about how the street light switches work. I did wonder how very cold or hot climates affect the operation though. ?
There's a 'new' kind of dusk-to-dawn lightbulb sensor, integrated into the bulb itself, that I'd love to know more about how it works. No photoresistor, I doubt there's any microcontroller. They are inexpensive, and work great in my experience. The light sensor is a LED, apparently. I know LEDs can be used as a photodiode, i.e., as a light sensor. What I'm most curious about is, how does it sense light when the Sun comes up, and therefore know to turn off, because the LED sensor is bathed in the light of the bulb. It's mounted at the base of the bulb, and in most fixtures, it surely gets lit up by the bulb. I suspect they turn the light off for a very short time, probably imperceptible to us, 'take a reading' of the ambient light, and go from there. Very interesting, AND probably much more efficient too.
Thanks for posting! Would love to hear more about how you tackle weather obs…
I used to have a 104 in 1 electronics kit as a kid. The photo resistor always fascinated me, but I always understood the solar panel better. This is such a simple and beautiful solution.
As a software developer, 17:05 made me actually laugh out loud. That hits really close to home, man!
I'm wondering if extreme temperature variations in some places might affect the operation of these things.
The power dissipated while "off" may also help to keep ice from forming over the LDR window, in cold climates. Love these videos. You do such an excellent job explaining electronics. Do you have an engineering background?
17:45 _"It's one thing to learn what a photoresistor does and quite another to make something happen with it"_
I made an input lag(motion to photon latency) tester for PC using a bunch of photoresistors that look exactly like the ones in your video but smaller.
I wired like 7 of them to an Arduino, then put them next to a PC monitor(spanning across the vertical axis of the monitor), connect Arduino to PC with USB.
I also wrote a DirectX program that would by default show black across the whole monitor, and when the left mouse button is held down, it would show white across the whole monitor.
Then I made Arduino send Left Mouse click to the PC and wait for the illuminance of the monitor to change from black to white using the array of photoresistors.
Arduino measures how much time passed between the moment it sent the signal to PC and the moment illuminance changed, then prints it to the PC console in microseconds.
Worked like a charm.
I worked for lighting design firm and designed layouts for streets, highways, and parking areas. But until now, I had no idea how the photo controllers actually worked. Well done, thanks for posting! And yes, striking an HID lamp requires a large amount of current and is hard on the lamp. A system that works slowly is critical to maintain the life of the lamp. Again, great job explaining the why in addition to the how.
Interesting. I've seen a different implementation. In the version I've seen, the photoresistor directly powers a large relay (that's the why the photoresistor needed to be so large -- you wouldn't need a large one for a thyristor version). The relay ones are "cheap" versions, and they buzz quite horrifically.
In 1981, I returned home from my three year Army enlistment. While I was adjusting back to my home time zone, I was a bit of a night person. I went on walks throughout the neighborhood and noticed many street lights out. Started recording them and phoning them in to the local electric utility. They were usually fixed within two days, what a difference for safety and security! I ended up expanding the reporting to include pot holes, traffic signs and signals, worn street painting, overgrown trees obscuring signs, etc. Did this for decades and yes, I have no life, but considered it part of public service.
That was exactly when I was thinking "hysteresis" and I am glad you said it.
A thermostat would eventually oscillate madly without it.
Many of our lights here had timers in the 80s and 90s but they were very traded out for these during that time depending on the cities planning.
When I was a kid in the 1970's and 80's I received a "Radio Shack Electronics Science Kit". It had many components mounted with springs to attach jumper wires to build projects. One of the projects was this exact device to control a night light. I don't know if they still make any educational toys like that any more. I certainly learned a lot from it.
I had one of those. Still have it, actually. Fantastic educational toy.
Hysteresis! (12:14 🤣) Very cool to see how the thermal mass of the system adds a delay without any complex circuitry, and prevents fast/erratic switching.
that one liner XD
I know what hysteresis is, but I totally don't get this reference lol
@kindlin Every time he goes "And this little doodad makes sure it waits the appropriate amount of time" someone in the comments will immediately "correct" him and explain that it's called hysteresis.
Ok, but it's just rate-dependent hysteresis. It's just a smoothing filter. Does that really count? It's far better than nothing, but there would be a light level where a tiny amount of variation would make it flick on and off intermittently.
Ideally there would be a rate-independent hysteresis with a proper bit of memory.
@Anders Juel Jensen Oh, alright, I just didn't know the word hysteresis had anything to do with controlling electrical circuits. I know the word as it relates to energy loss over time or work done; specifically, seismic energy dissipation.
Great video Alec! As a side note I would like to add please but a reputable brand of photocell or fixture containing a photocell like RAB or lithonia. Make sure you get a fully molded photocell so the water on an exterior fixture doesn’t get in and ruin it. Those cheap Home Depot or Lowe’s lights always fail prematurely. I have been doing electrical work for 10+ years
This makes sense. I've never had the time, nor thought to open one of these up, because the generally don't fail.
It also makes sense in another way, when the sun is out, they get warm just from that, so even if the power does fail, unless it's very cold and windy, it's not likely to have that little flicker of on and than back off again.
The not-sketchiness of that totally legitimate street lamp setup was comforting to the soul for its sheer inherent safety.
Very interesting to see these simple devices. There are already smart versions of this made by companies such as Crestron, Wattstopper, Hubble and more. They not only are digital controls but are networked to allow for fine tuning and dimming capabilities.
Hey Alec, I've long wondered, do you always make those frustration noises we hear in the bloopers, or only when you're recording?
It is sadly not inconsequential if all street lights turn on after a power outage. Makes black and brown starts of a grid even more of a nightmare than it is anyways.
nowhere near as not inconsequential as everybody's electric climate control system trying to start up is though.
Eh, compared to all the other loads that are immediately trying to come on, I doubt it's significant. Besides, the power grid has to handle _all_ street lights coming on within the same 10-20 minute window every evening.
@Technology Connections Not really, group control will take roughly an hour to switch the entire metro on or off, as each group photocell has varying amounts of shade on it, and the light levels are not too tightly controlled as to exact switch point, that has a pretty large variation between each photocontrol. Biggest thing is all those cold water heaters all sitting there already on, waiting for power, that is a massive surge.
@SeanBZA Those are all resistive loads so not that big of a deal on grid restart. The inductive loads of motors though, like in HVAC systems, are a big issue with inrush current causing voltage droop.
@Technology Connections I would agree it's inconsequential, but all the lights coming on over a 10-20 minute interval, but staggered due to variations in the detectors and their local light condition is entirely different to simultaneously switching them all on when power returns.
Great video, like always :)
Instead of a microcontroller based solution, I thought about a Schmitt trigger using an OP-Amp (switching an off-the-shelf relay, maybe). Would be very robust, cheap, and consume less power than a heating element. There are probably reasons why it is not done that way, but I just cant think of any in particular.
This video presented a new method to me. Without a microcontroller, I only know of those that use an OP-Amp, Comparator or even 555 timer with a relay.
I started.playing around with different types.of photoelectric light controls back in the early 1970s when I was about 14. I took.many.apart to see exactly how they worked. One.of my favorite designs was the thermal relay. Very clever way to incorporate a delay so that flashes of.lightning or flashes of car headlights don't trip the control.
Hi Alec. Your videos are amazing. IDK if you knew about the early TV museam in Ohio. I never thought i would be interested in old school electronics but it is very fascinating to me now.
As a small kid, I can remember asking multiple times, "who turns on all these lights?" when on the highway.
For a component that sits in the hot sunlight all day long, it makes sense to use heat to keep the light off.