Inside a UK compliant dusk sensor switch. (with schematic)
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- เผยแพร่เมื่อ 20 มี.ค. 2020
- This unit is clearly made down to a price, but it still manages to be a good logical design.
In a sense it almost looks a bit old fashioned, but if it works then it makes sense to keep using the same circuitry. It's very similar circuitry to the cheap eBay boxy looking dusk sensors, but with proper cable connection facility as opposed to the slightly shady individual cores on the Chinese ones.
These units are also designed for easy maintenance. If the circuitry fails or the relay welds shut with a high current load or fault, then you can just twist the old unit off and twist another on. There are also bypass versions that bridge the live and load connections for testing, and there are more specialist versions with smart circuitry that measures the length of the night and then switches off at a surprisingly accurate mid-darkness time based on the previous night's duration.
I've installed this to test it and also to test some LED festoon for storm and time resilience. It was easy to mount, but did require four core cable (don't use earth as a circuit conductor, even if sleeved).
Products like this make you realise that the humble 555 timer chip is not going away soon despite being one of the earliest integrated circuits. Even the name "photocell" is a hint to the heritage of these units.
There's an error on my schematic. The MOV transient suppressor is across live and neutral and not across the contacts. I guess it's probably to protect the circuitry, especially the dropper cap.
One thing that might have been an interesting addition is an NTC inrush limiting component to take the switching stress off the contacts. I'm not sure if the extra heat it generated would be an issue though. Now that I've just typed that I've realised that the 470 ohm resistor will be acting as a heater. I've just calculated that it will have about 24V across it and dissipate about 1W at 50mA. That's possibly to keep the unit slightly warm for reducing condensation and stop snow from sitting on the sensor. That's clever. It also explains the 2W standby power. Just over a watt for the heater and about 0.75W for the zener. (15V * 50mA).
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
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This also keeps the channel independent of TH-cam's advertising algorithms allowing it to be a bit more dangerous and naughty. - วิทยาศาสตร์และเทคโนโลยี
Back in 1967, when I was a teenager, a friend and myself did a 4 day camping trip in a US National Park. This was just after the US Government had dumped huge amounts of money upgrading the National Parks and their infrastructure with a project called the Mission 66 project, celebrating the 50th anniversary of the National Park Service. The campground had brand new restrooms and I noticed they had put dusk sensors to turn the lights in the rest rooms on at dark. The sensors had no time delays in them. I recognized that fact and we teenagers, doing what teenagers do, hid behind a bolder and shown our flashlights on the sensors causing the lights to go on and off while listening to the cuss words coming out of the restroom.
a bunnch of bla'-guards hiding!! in the rocks shining lights all nite.. sounds like good alue times!!!!
Mustard mitt that I, at >60, have done this. Modern LED torches with nice tight beams mean you can now do this at considerable range.
@@Graham_Langley its a site altogether when ya look back and it's at the silliest of things ya found funny & still do!!!!
I just like it when Clive does a tear down, reverse engineers the thing, takes the closeup pictures, draws the circuit diagram and then explains how it works. Very interesting and informative. Thanks 😊
Indeed! Me too!
everyone: we need to panic buy toilet rolls
Big Clive: I need to panic buy spiral notebooks and purple pens
Shipping clerk: Six gross of purple pens for the Isle of Man?
Shipping supervisor: Big Clive...
Shipping clerk: Oh. Right.
And LED lights of various types. Here's a video of Clive's light collection, set to music: th-cam.com/video/pWBjl-jPcVM/w-d-xo.html
Interesting use of the classic 555. I'm not sure that I've ever seen it being used in this particular configuration before. Nice to see a 50-year-old IC being used in modern products. It just goes to show what a superb design this tiny chip was that it's still being used all these decades later.
I really enjoyed the explanation on the time delay circuit feeding into the 555. Every time I watch one of these videos i always learn something. Thanks BC!!!!!!
We all wish we had another 1/4 inch on the gland end
Don't use a gland! Ziptie the cable on the inside for strain relief and let any excess moisture drip out the bottom.
It's the glans, not gland.
What's a 1/4 inch between friends?
It is nice to see the young interested in technology too.. ;-)
I like it when you point out the most common point/component of failure.
So what's the alternative for people in other countries that don't have UK-compliant dusks?
Before you start looking for an alternative dusk sensor, check if you live in Canada, Australia, India or any other country in the Commonwealth, as they should all have UK compliant dusks and dawns by order of the Queen.
@@Gameboygenius wtf order of Queen 🤣 ? Is IT a joke ?
@@pierre-alexandrelemay1720 I don't think so
@@ghmusic8116 _Whooooooosh_
That was the sound of a compliant dusk going right over your head.
@@pierre-alexandrelemay1720 I can understand why some people might not have got my original joke as it was rather subtle. Gameboygenius expanded upon my joke for the benefit of the hard-of-thinking. You still didn't get it...
The time delay on power up is legacy from the mechanical ones, it's a handy feature that will test the light strikes, and normally won't be an issue for the rest of its life.
To get around the problem if using a timeswitch, connect the sensor direct to the supply, and run its output through the timeswitch contacts (timeswitch would also be permanetly powered)
I've lost count of how many of those we installed
Now you are trying to explain an advanced circuit for average Joe. We electricians already know about this but your target group is DIY who should not tinker with that stuff. Besides that, it would involve some wiring back to the box and a lot of colors to keep track of. The perfect source for errors.
Fitted this exact model today. I tend to stick to this type love the fact the head can be swapped out if it fails. Wondered why there is always a delay when you cover the sensor to test. Now i know...thanks Clive. I will tell my customers next time I fit one to make me look smarter than i actually am!
Clive, we have every faith in your ability to sort out your glands.
I must have fitted dozens of these. Reliable, rarely fail. 555 timers must be about the most adaptable components , excluding microprocessors.
Do you have the approved " test rag " to , you know , test it with ?
Wonderful seeing a 555 in the 21st century when most engineers would probably use a cheap microcontroller.
I'm no electronic engineer but I'd used something like LM397 a voltage comparator.
@@koitk I feel like that would cause flickering in the case of say headlights or the strobes on an emergency vehicle.
Thing is, most probably a cheap modern microcontroller would actually only draw a fraction of the power a 555 draws...
@@frabert Yeah, but this thing is made for mains powered lights so even a 555 is minuscule compared to the primary draw. I think we're seeing more micro's because that's just how engineers are trained now a days. It's refreshing to see a classic simple circuit based around an IC with a grand total of 25 transistors.
It makes a grumpy old bastard like me smile.
@@rayceeya8659 I have to be honest with you, I don't understand your point. Using a microcontroller would (maybe? I don't know the exact economy of scale here) be cheaper, more efficient and maybe even smaller. It's just a better solution all-around, to me. I see no point in using something more specialized if it doesn't make the job easier or more efficient.
Thanks for giving us something else to think about in these troubled days!👍
These are excellent pieces of kit. My preferred supplier is TLC Croydon (for reference). Damn good service and they sell proper equipment!
I've been using one of these outside for a couple of years and it's always worked fine. Seems a decent design
I remember in 1993 for work experience I was working with an electrician company who were replacing the older system in blocks of flats for the local council and I was able to to get a complete 'used' system of sensor, time switch and external light fitting.
@@johncoops6897 Well it was going to be disposed of so technically recycling something that was just going to put in some rubbish tip. This was because it was the contractors responsibility to dispose of removed equipment and no longer the responsibility of the council.
555s are my favorite IC :)
Although, I'm definitely a novice in the building of electronics. I think I just love how flexible they can be for so many different applications.
I have a small pack of those exact same 555s that I'm going to use to make some PWM led dimmers.
haha I'm a professional engineer and they're my favorite IC too.
I think it's definitely the favourite IC of most engineers and enthusiasts of my generation, probably because it's just SO versatile, and it's always cool to see old devices like this in applications where modern designers would just use a microcontroller. The thing is, if the 555 ever failed (very unlikely as they're really tough) you can just replace it. With a mirocontroller, it has to be programmed so you'd need access to the programming hardware and the code as well, which is not always an option for independent repairers. OK you wouldn't normally do a repair on such a cheap device (I would if it were my own, but you could never do it commercially) but you get my point.
While microcontrollers are great, nothing beats good, old-school analogue designing - it's just so much more fun :)
@@countzero1136 I mean, I don't know what generation you're in, but I'm in my mid 30's and have been slowly learning electronics and circuitry. For the super basic stuff I do, the flexibility of the 555 and a few others means you can do SO MUCH.
I think one thing I love about learning basic circuitry is knowing with a handful of basic components and a breadboard you can create something that does just about anything you'd ever want.
That's SUCH a cool experience. There's creativity, science, engineering, and a final result that's just so fun for me. :)
Many, many years ago I built a motor speed controller for a remote controlled electric model speedboat for a friend. The boat had a 12V motorcycle lead acid battery powering it and he was trying to control that either resistively via a potentiometer or a big bipolar power transistor. Neither had a hope of working for very long because of the amount of power that they'd have to dissipate at half power. They'd just nuke out and die. But it occurred to me that if I used a 555 to produce a square wave at a few hundred hertz and then varied the duty cycle ( PWM style ) with a small potentiometer passing almost no current and then fed that square wave into a couple of mosfets, they could control the motor speed. Since the mosfets were either off or on, there was almost no resistive heat dissipation. I mounted the mosfets on a big heatsink anyway, just to be safe and put the 555 and associated components on a small pcb on the reverse. It worked really well, and was the terror of the local duck pond.
I had one back in the early '80s which had a large LDR connected in series with a relay coil. The relay used to chatter like crazy as the coil current approached the switching threshold. It was originally used to switch the outside lights at a primary school I went to. The pins on the back were identical to the one in this video.
Good old 555 timer, threshold detector and relay drive :-D
One of the many things a 555 can do.
Odd name for an IC without a clock in it !
@@millomweb by the way that chip can be used for a clock.
Pretty easily.
But yes I like the point I thought about that years ago I first heard about those Champs and got to wondering about it.
You'd be surprised how many uses of slaves have besides being a timer.
For example this circuit 40 on at dusk off at dawn switch photocell as we call them here in the United States.
Also called a full electric switch.
By the way as big as I was saying about the older ones that used to big ldr light dependent resistor and a thermal relay a bimetallic strip and heater that is.
I have seen even some more modern photo controls that would mount in a junction box on a plate or inside a pole light.
That are about as big as a dimmer switch maybe a little smaller at least the internal package.
Those at least most of them I've seen work the same way.
Also I got an old photo electric switch that had a cord on it a big round bullet shaped kind of thing they used it for the chicken coop at one time.
Used it for about forever but one supposedly died.
A trip to the park to see what I could Salvage it turns out it was the same type of thing as the old school ones mentioned above.
Also from the same person I got old time switch.
AKA altered time clock.
That was used for the same an application at one time. And a chicken coop.
It actually had two outputs that triggered at different times to simulate the the sun setting so the chickens would return to roost.
Evidently chicken for return to roost if the lights are suddenly cut off instead of getting dimmer.
And also they need 14 hours of light for egg-laying evidently as well.
I also got some other things from them as pretty interesting stuff I found over the years.
That photo switch the one the bowl Chapel on we use on their garage light for years for the outdoor light.
Was a flood light for the backyard where are dog tie out was.
Then I switch you to a timer that is old time switch I got from someone else.
The later on that light was replaced with one on the side of the garage it was old high pressure sodium.
What I call wall box fixture with a built-in photocell.
Can't remember where I got it but it was when they were updating a building and they had tons of those.
I think it was somehow I knew that worked at a place.
Either or get weed electrician or something.
@@millomweb Why odd? Time delays and clock generation from RC circuits goes back to the dawn of electronics.
My first use of a 555 (x2) was to make a Star Trek "Red Alert" noise generator. :-)
@@aaronbrandenburg2441 It's only a switch - that's like saying a pendulum can be used for a clock !
A 555 timer. What a Gem. Nice to see them still about.
I put two of these on my house (Part P - ahem) - one is the dusk to dawn type you showed. The other has the extra components in it to calculate solar midnight after a few days and then it switches off late at night and on longer nights in the winter, switches back on again early in the morning.
Think John Ward recently showed a very similar sensor switch. He didn't go into the circuitry detail like you but showed the external wiring setup.
Love the 555.....have built lots of little led thingies with them.
We used to fit two different types of that photocell, the P3 was basic with a bimetallic strip contact's and a heating element controlled by the photocell and used on road sign lights.
The P5 was like the one you have there and used on street lighting columns, but even back in the 90's we were using more expensive SELC units that were more refined and prevented lights coming on simply because of a storm cloud passing over.
These days they are fitting units that are controlled using the old analog cell phone networks. Using remote control one of a group of lights has a master controller and the others have slave units. These groups of lights can be turned off at peak electric demand, or turned off at midnight as a cost saving measure. Because they are coded they can select which lights to turn off and which they need to keep burning, depending on how busy a junction or street is.
Where is the other video gone? The one titled "this phone can detect people with the coronavirus from a distance"? I've seen the notification but haven't had the chance to watch it yet! When I did, it was gone :-( Please, Clive, do not self-censor your content, you are too good for that (as is your content)!
th-cam.com/video/WZWZ-UgnbXg/w-d-xo.html
@@bigclivedotcom Thanks!
Where I live they use either blue or red-brown sensor modules, with the actual light detection diode/resistor being on knew side of the unit.
These are mounted to the underside of the street light unit, meaning if the lights are on a road which runs East-West, the lights with the east facing sensors will all turn on first. So you get this weird effect where all the lights on one side are on well before the other side.
I remember the old days of using a large PE cell and a bimetalic relay.
Damn... I missed the coronavirus phone detector video. I guess YT didn't appreciate the big clive sense of humour. Naughty naughty!
th-cam.com/video/WZWZ-UgnbXg/w-d-xo.html
another cool thing learnt for the day.. thank you Clive your a pure legend.. and ya! given me an idea with that tear down,, CHEERS!!!
The voltage dividing part that goes to the input of the timer would explain why you would sometimes see street lighting flashing on and off before eventually stopping on, the capacitive dropper failing could also cause the relay to cycle aswell.
13:18 @bigclivedotcom that diode on the output of the 555 is to keep the reverse voltage spike from the relay coil from back feeding into the 555. otherwise soon as the relay is turned off there is a significant reverse voltage spike that would kill the 555 timer. Normally the diode is placed across the relays coil contacts but as long as the diode is able to prevent reverse voltage spikes it don't matter where it is. That circuit basically has two reverse current shunt diodes :)
Nearly. It's there to convert the push-pull output of the 555 to single-ended. Without the series diode the lower transistor will pass all the back-EMF current as it will short the relay coil when the output is low which may put a damaging current through it. Putting in a series diode means the parallel diode can do its job.
Hi Clive did you observe the North arrow on the base case just like the old bimetallic type. There LDR’s were sprayed black then scratched to set the on time value. The failure of the old Royce Thomson was the flexing of the red wire to bimetallic strip used to break off. Not sure if it was the flexing or heat from strip. I still have a couple with the remote LDR. Still working fine too. Another great video thanks Clive.
Looking as a nice simple circuit
Thanks for sharing :-)
We used a much more rugged version (glass cover) of a similar device, in conjunction with a solid state relay, and Austin ring transformer to turn on tower lights at dusk on AM broadcast antennas.
As always, excellent explanation
Even with the bimetalic style, the delay was useful with street lights for lamp test purposes. The delay would be enough to check the lamp strike properly. Obviously it wouldnt show a failing lamp but by removing and replacing the slidelock fuse at the base it was useful
LOL, we had one installed yesterday, and the poor guy stood for 15 seconds with a cardboard box over the sensor to test the circuit, and repeated several times due to faulty wiring...
This excellent video is rather good timing as I have one of these attached to my electronics shed that's failed, and I've never gotten to taking it apart to find out why. Armed with your schematic I can do some fault finding now!
watch out because the capacitive dropper means its directly connected to live mains...
Thank you clive, so intresting!
I never would have imagined a 555 was used to drive a relay directly... (despite the fact that I have studied some electronics, I've only seen it used as a timer device, but I know it's used for much more than that...) So you tought me something new today! :)
It can switch about 100mA. That's why it has such staying power. Multi-use with threshold detectors and a high current output.
I watched some LED lights in a Wal-Mart parking lot rapidly flick on and off when it was cloudy last week as people ran to get what was left in the store. Now I know those lights were missing that extra capacitor that Clive mentions at 11:45. Those lights will probably fail soon all because of a 3 cent part missing.
More interesting than I expected.
I've had one doing its thing for about the last 15 years! Agree with other comments, turns on a bit early (not quite dark) and keeps on when daylight.
Nice teardown and review. I have one of these photocells but from eBay rather than an outlet. Will have to see how it goes; we currently have PIR based lights and the PIRs always tend to fail over time, so we're upgrading to a photocell based light.
Will have 2x LEDs and 1x CFL running off it :).
I designed a machine to press those brass lugs into the plastic base. Customer really liked it.
Proper photocells are the old thermal type with a giant LDR and a heater resistor attached to a temperature compensated thermally actuated microswitch mechanism. No semiconductors required! Takes 3W in full sunlight and nothing at night. The warmth drives off any moisture which might get inside. Lasts for years until the spring in the mechanism finally gives out!
I used a blind rubber grommet (cut in a cross to allow the cable through, no worry about the unit filling up with water as it can still drain) instead of the gland on the timed-off version of these when I installed them on my house. Still good 5 years on, so no water ingress.
Same circuit as the dusk switch you did previously except that one used the LDR (light dependent resistor) from May of 2017. Nice app for the 555. It will not trigger immediately if a cars headlights hit the sensor at night or if lightening flash hits it. Nice side effect. I built a few for myself since then. I used an Optocoupler to drive power triacs instead of a relay to control the mains. They are working great 3 years and counting..
Why waste an optocoupler when entire circuit is live at mains voltage?
@@johncrowerdoe5527 Mainly for built in zero crossover switching circuitry in the opto. Saves on electrical noise and surges into your load.
@@jp040759 Ahh, the wonder of chips with unused functions for the job, just like our friend 555 .
They were sometimes used without the wall bracket when the socket was built directly into the top of a lighting fixture such as a street light lantern.
Got one of these on the light for a house sign. Was surprised quite how warm it gets.
The one thing I know about these, the connector is a US NEMA Twist-lock plug & socket setup, used across the pond where it's likely that someone could pull out a regular plug from the wall (such as for a camper, generator, outdoor power equipment, garage/workshop, etc.), not sure which pin/voltage variant these are, but guessing it's a 20 Amp-type sized version... :)
(Though connecting the sensor to an actual twist-lock socket would result in a bit of a bang I'm sure!!!)
Yeah, looks like a NEMA L5-20p/r (120 V) setup but maybe the device is configured with a different blade set due to most having a slight bend on the grounding blade.
It depends how 'badly' the thing is wired. If wired completely wrong, it'd be fine. The device is a switch connecting 2 of the wires together. So Lin and Lout will get connected together - so for these, use the pins for neutral and earth - connect those together, no bang - leaving the unit's neutral wire to connect to live feed. The switch would then work but all it would do is connect N to E.
@@millomweb Which may either trigger or bypass your GFI.
@@johncrowerdoe5527 It should trigger it. But still no bang !
Thanks Clive Stay Safe my friend
The series diode in the 555 output is there to convert the push-pull output to single-ended - without it the back-EMF current from the relay will go through the lower transistor and not the parallel diode.
I'm a big fan of having my gland near to the insertion point.
I’ve missed you bigclive! You’re the best for Coronavirus 👍
You could probably move the connections of the 100uF cap so it's +ve is on the 15v rail and the -ve is connected to the 20k resistor and 555. At power with the cap discharged the input of the 555 would be pulled high instead of of low, so the relay would not be energised.
skywizardless...I was waiting too see if any one saw that design option...great pickup...designed many similar ccts and don't understand why it escaped the original designer...i.e. zero cost
@@mekuranda I did wonder if the 15v rail sagging when the relay was energised could cause problems. In the original design this would effectively introduce additional hysteresis i.e input goes high enough to trigger 555, relay energises, 15v rail drops and so do the switching thresholds in the 555 but input voltage stays the same. With the cap to 15v rail this additional hysteresis is lost as the input will follow supply rail transients, but there should be enough hysteresis from the 555 anyway.
Oh it’s one those 5G death ray thingies people are talking about! 😝
Somewhere on the top part there will be a mark, and you can orientate the lower part of the bayonet socket such that the mark on the upper part faces north, or as close as possible.
I did that. Partly to point the sensor away from other light sources.
The "mystery" diode in series with the relay coil is to make sure all the flyback current when it turns off flows through the external diode parallel to the relay and not through the intrinsic diode within the 555 IC. The point is, all the circuit packed on a common silicon substrate has a drawback: Parasitic structures (mainly transistors are the pesky ones here) that may form unintended and not much controlled feedbacks in the circuit, making it not work (or with more modern CMOS those parasitics tend to even form a thyristor short circuiting the supply once activated, yielding immediate destruction). These parasitic transistors are unavoidable and their arrangement and parameters will vary among manufacturer and the generation of the seemingly the same standard IC. So the only way to avoid any problems, the application circuit designers should make sure the parasitics are never ever activated, here this extra diode.
Bought a Red Arrow branded one of these from a CPC flyer a couple of years back to gut and use to house a light sensor.
Its PCB was mounted copper side up making soldering /desoldering the contacts a lot easier at the expense of having to hand-solder the relay, pot and photodiode. The pad pattern for the contacts looks identical to yours so I guess one firm makes the case and others put their PCB in it.
The 555 side of the cct is absolutely identical but used an unbranded open-frame relay with very chunky contacts. The PSU side used a 100n dropper cap with no series resistor and the MOV was between L & N . [Edit] Just read your correction re. the MOV.
I'm pretty sure the new one of those we just installed on the outside lighting late last year still has the bimetallic strip/CdS-controlled heater inside... (USA)
As far as I'm aware Tork, Longjoin & Fisher Pierce still produce the cadmium/Bi-metal strip type.
If you move that 100 microfarad so it's it's connected to the positive rail instead of ground, then the device will power up in the "off" mode and there would be a turn on delay if it was dark.
But why would you, though? Think about it. Would you rather... have the lamp light up for a couple of minutes if you screw it in during daytime, or stand there in the dark for a couple of minutes if you screw it in during night time? One of those options could clearly be much more annoying than the other.
@@johncoops6897 I can certainly imagine a scenario where one of these fails at night time, and gets replaced.
@@johncoops6897 Does this flimsy thing look like something the city would put up? This clearly you'd put up on your own house.
@@Gameboygenius He was just making a point which was rather smart not that it would be any use, dumbass.
@@johncoops6897 who said anything about wring it at night? Doh!
Fitted some of these recently, they are tricky to wire especially in fp200! They were being used to switch some new led hi-lo lights in communal flat stairwells. The lights had their own built in photocells but the management company insisted we fit these and disable the built in photocells.
Yeah, FP200 would require careful shaping.
I guess the one I have (from the 80s) is of the other type as I think it has a large tube pointing up to the centre of the outer cap. Also, the click from it sounds a lot heavier than relay contacts ! It isn't a plug in and twist but pre wired with three wires coming out of it.
We have a newish LED street light and yes it has come on during a passing cloud and gone off again - whereas this old style thing would have ignored the cloud.
I wonder if the fact that it briefly turns on when first energized was a purposeful design decision. It will tell you that it has power and is working without having to block the sensor or wait for dark.
I think a useful side effect rather than purposefully done.
Clive, the diode on the output of the 555 is to stop the relay turning on by the 555 sinking current due to it being driven from a capacitive dropper from an AC supply...I seem to recall!! :)
More likely latch-up protection.
I have been wanting to see what is inside these commercial ones. Kind of surprised they used the humble triple five. Thought there might have been some kind of micro controller! Although this circuit could have been done with the Schmidt Trigger style arrangement with just two transistors. Then a 24 volt relay could have been used and the overall dissipation of the unit reduced substantially.
The connectors that these use on their bases is a NEMA connector - a North American standard. It's of course is a "twist lock" and looks similar to the connectors that are used in the US for generator power leads etc.
Some domestic extractor fans have an on time delay so if you briefly go in (PIR sensor) or turn on the light in the bathroom/toilet, the fan won’t immediately turn on.
In re the delay/hysteresis: could you do something similar with a Schmitt trigger? I am very much an amateur, and would be interested to learn why this wouldn't work when the 555 does.
It's being used as a single Schmitt trigger. The advantage of the 555 is that it's common and can drive the relay directly.
This PCB use IC555 different than Zodion photocell ss4.Hope to durable to use.Thank you for your teardown analysis.
That photocell socket is very similar to the 30A (American?)Hubble connecter. We still have some of those in our theatre for the 5 KW dimmer circuits!!
Was going to comment the same thing! You're probably thinking of the Hubble L14-30, very common in the production/entertainment industry in North America. This looks like they use something similar to the L5-20
Zener diodes are named after Clarence Zener, and he pronounced his own name "zeener" (although the name is originally germanic, and pronounced closer to "dzehner").
I've always pronounced it zeener, but it seems to get a barrage of corrections every time I say it.
@@bigclivedotcom +1 for zeener as the other pronunciation it should rather be written with double n in the middle: zenner
Or, to put it another way, it "enhances viewer engagement" and "promotes target audience interaction". ;^)
Great video bigclive
Regarding the “question mark” diode. I sometimes see these in other relay circuits as well. My best guess is that they are protecting the output transistor in the 555 against a brief positive voltage spike that happens when the relay coil resonates with the capacitance of the parallel diode on relay turn off (the parallel diode doesn’t discharge the coil cleanly, but often there’s some ringing after switch-off). In my experience it’s never been a problem, but it seems some designers believe otherwise.
avian6 I had never thought of resonance there, interesting idea.
My first though is that the mystery diode is reducing the negative voltage on the 555 output pin while the fly-back current of the relay coil is dissipating and allowing one diode drop below the negative rail due to the coil snubber diode.
Could it be that the small negative voltage on the output pin could otherwise lock up the 555?
Otmar Ebenhoech That also sounds plausible to me.
@@CafeElectric That was my first thought, but thinking about it again it's more likely to stop the lower transistor of the push-pull output stage passing the back-EMF current when the output goes low which might embarrass it . The series diode lets the parallel diode do what it's there for.
The pins and socket are similar (same?) to those commonly used on US street lights and smaller area lights. The detector fixture itself is quite a bit smaller and mounts directly on top of the light housing. It has been decades since I changed one or took one apart but we can still see that little bump on top of many lights.
I think they're common globally.
Thank you BC!
@3:05 - I'm in the USA and I have never heard anyone outside of an OLD electrician friend refer to "RAWL" plugs. Back in the day, we used jute and lead sleeves to fasten things to a brick wall. They were "RAWL" brand and they are the best you can get IMHO.
Here in the UK, Rawl has become a generic name. Even though it's technically a brand name, the term "rawl plug" has come to refer to all kinds of screw fixings designed to go into masonry. I use the term all the time, though I haven't seen any bearing the Rawl brand name for many many years. It's a bit like saying you're going to google something, or do the hoovering :)
@@countzero1136 I jumped down a rabbit hole and read as such. I love learning new things. That's a really good reason to watch Clive. Thanks for the reply, mate!
@@countzero1136 Indeed. One has to be very careful when writing installation instructions and refer to them as wallplugs.
I don't think it's a MOV is across the relay contacts as shown in the schematic. It just appears to be across L-N in the usual surge suppression config.
I have had one of these in the cellar for years with the intention of using it to control outdoor lights, but have never quite got around to it and am using the all-in-on sensor bulbs instead. The downside of those is that they need to turn off periodically in order to check if it's still dark...
The way to get around the time switch situation is to use the time switch to operate the neutral to the load while leaving the neutral to the sensor unswitched, needs an extra neutral wire though. Or put the time switch between the sensor and the load but that needs 2 extra wires.
Best way to test these are with a parcel tape roll wit black tape on top they fit perfectly,
also a small point there is an arrow on them that you need to align with the north.
The Diode on the output of the 555 looks like a blocking Diode to block the Voltage from the Relay coil whilst the Free Wheeling Diode does its job.
Agreed - the 555 output is push-pull so the back-EMF current from the relay will go through the lower transistor and not the parallel diode if the series diode wasn't there.
Great video.
Is that one where there is an arrow on the socket that has to be orientated to the North when fitting it?
Darn it now I've got to go look at the one I installed.
Clive, happy new year. you deserve to invest in a big bear of a soldering iron that can unsolder such joints. Excellent fellow TH-camr d-lab electronics calls it “the schnauzasaurus”
I do have a monster iron somewhere, but it is so rarely used that it's buried under other stuff.
Could you not put the timeswitch after the dusk till dawn switch, then it doesn't matter what the dusk till dawn switch does on powerup
The diode in series with the relais coil could be used to get the voltage down, since the PSU is about 15v and the coil is meant for 12v. Not sure if that realy is the case, but it could be. I've seen diodes being used that way in audio mixers too, where the PSU is 18v and they use effects modules designed for lower voltages. Soundcraft for example has 18v PSU, and they use lexicon effects boards with 3 series diodes in the power line.
I was thinking it was reducing the reverse voltage from the coil. During turn off the coil will produce as much negative voltage as the flyback diode lets it, so typically 1 diode voltage below zero. The series diode raises that up again by 1 diode voltage, so the 555 pin is only negative by the slight difference between high and low current diode drop for whatever diode model is chosen by the factory purchase manager.
@@johncrowerdoe5527 A 555 should be perfectly capable to handle that, but you could be right.
When that delay capacitor fails, the light spends 30 minutes to hour turning on and off at dusk and again at dawn. It's quite annoying outside one's bedroom window. :)
If it fails low capacity, it reacts faster. If it fails short the light is permanently on.
@@johncrowerdoe5527 I don't recall ever seeing a capacitor fail short, but maybe that's what happened to the ones (not in this circuit) that exploded.
It's not the delay cap failing, it's when the light sensor can see the light it controls. Some stupidly bright omnidirectional light fittings have been installed around some flats near here with the sensors well within range of them with the predicable result - in one case the sensor is right next to the light.
@@Sylvan_dB The only caps that regularly fail short are those horrible layered SMT jobbies that infest modrn equipment, and those horrible tantalums you get in 80s and early 90s computer gear. I've seen shorted tantalums on PC cards that prevented the whole system from booting up. I guess it's a result of trying to cram a bigger and bigger capacitances into ever smaller spaces, so the dielectric layers get thinner and thinner, so even relatively small voltage transients can easily break through.
Capacitors are a proper menace to anyone in the repair trade, as we all routinely replace electrolytics but often neglect the smaller ones which are very common failure points in all kinds of equipment :(
@@countzero1136 Replacing SMD MLCCs is made harder by their complete lack of markings. Without knowing what capacitor to use, there's no way to figure out by looking at a broken device. Same size resistors are marked with their nominal value in a simplified form of the old color codes. Larger ceramic capacitors have their values written on the size.
I wonder if that big 470 resistor is also doing a bit of "keep the whole thing kind of warm" to drive out moisture that happens to get inside.
I realised that afterwards and added a few extra details in the description.
That's allot bigger than the ones we use here in the US. And what's funny is yours uses a standard US 220V twist lock plug. The ones we have here in the US are crap. Very failure prone and most places just wire around them and go with a switch or a timer. You can always tell the places that have a timer instead as their lights don't come on when there is a storm or when it gets dark early in the winter.
Although the quality of this looks to be quite good, I wouldn't say it's of the standard used in street lighting for one reason and one reason only, on this cell it looks like the load is wired through the "normally open" contacts on the relay (that's how the two I have are wired anyway) which means that if the electronics of the cell fail, the load wouldn't be activated which could be potentially dangerous. With a proper cell like a Royce Thompson (Zodion used to be reasonable but their modern ZCells are exceptionally low quality) the load is wired through the "normally closed" contacts so that if anything goes wrong with the cell, the load will be activated 24/7 which is much safer and also more likely to get the problem noticed quickly.
I had a power-cut recently and the said mentioned sensor is no longer working.
Do you think that I only need to replace the sensor head? Rather than a whole unit?
Many thx 🙏🏻
I think that diode is there to protect output of 555. When 555 output goes low, relay coil keeps current flowing for a while and without that diode it would pass directly through that output to ground.
Agreed.
The other thing i was curious about is at around 0.39 you will see a capital N on the socket. Does this mean point this to North when fitting so the sun sweeps passed east to west... think so
I'm willing to bet that the light sensor is not a Photodiode, but rather a Phototransistor. Circuit makes much more sense with one.
Going in this video I fully expected this to be a re-badged Zodion (google "zodion ss4d" for fun) product, but it wasn't.
I own a spare light sensor for an outdoor light with a similar circuit, but instead of the 555 it has a LM358 that compares the light level to another set level. That circuit does require and is equipped with an additional transistor for the relay, I believe. I'm too lazy to get up and get it.
Thanks clive as always so informative. I'm preparing for the worst right now. I live in a block of 25 mostly vulernable and elderly people. I have been preparing myself to jump in to action with my mask and gloves at the ready etc.... What might be a good idea is a loud sound device that can be made with simple electronics for older people that will struggle to use a phone (hopefully most have this already)...its just an idea I have for your next video (maybe? you probably have already?)
It sounds like a classic pocket "rape" alarm might be ideal.
www.ebay.co.uk/sch/i.html?_odkw=panic+alarm&_sop=15&LH_BIN=1&_osacat=0&_from=R40&_trksid=m570.l1313&_nkw=rape+alarm&_sacat=0
A 555 with an old speaker and an on button works very well. Uses no battery until activated. Variations in resistors or capacitor can give each person a different tone. Should run fine from a fully charged 18650 cell or 3 alkaline cells, as either will be above the 4.5V minimum (max is 18V). Capacitor sizes needed would be 1μF (for frequency and power supply), 100nF (for power supply) and 10nF (for pin 5).
An alternative design is the classic two transistor astable multivibrator using 2 identical transistors (PNP or NPN, whatever you have), 4 resistors and 2 capacitors, plus the speaker, power button and battery.
@@bigclivedotcom great thanks
perhaps the diode coming out of the 555 drops the voltage for the 12v relay.
Scott Tuttle I was thinking the same, although not sure why they couldn’t just have designed the supply to provide the correct voltage...
Almost missed this, that thumbnail was a bit different than usual
I'm surprised they're allowed to have such a high standby power dissipation of 12VA and 2W, yet still comply with the regulations. The power consumption could be drastically reduced by using a CMOS 555/comparator/74HC1G14 and a TRIAC, preferably a sensitive gate one, so it doesn't need a large trigger current.
I would think that it would be a photo-transistor rather than a photo-diode. Usually photo-diodes produce fairly small reverse biased currents, I don't think a photo-diode would provide enough current to cause a large enough voltage swing with the specified resistances.