today Gordon's going to explain how smart doorbells work ding dong terry thomas going
i'd like to take this one gordon but i feel it's probably more your patch to explain how a smart
doorbell works well gary got away lightly on our last video where we installed this netatmo
smart doorbell in our smart home takeover yeah and that install it that went swimmingly well didn't
it go we managed to get everything working first time without any problems now you may have arrived
at this video because you've installed a smart doorbell from various brands and you're having
some problems so what we're going to look at in this video is how the system works and some of
the problems you can encounter and specifically how this little clever little black box here the
chime module works so you built this rig to support the evidence of how this is going to
work gordon is there any bits in here you want to highlight to us um i guess the the key thing
people forget about smart doorbells is the way the actual work themselves in terms of most of them
have an actual battery inside and you have to keep that battery charged remember the
battery's there for functional purposes that we'll come on to later but these are
powered off the bell transformer that's already in the circuit right okay and we didn't change any of
the wiring did we were in that smart home takeover we used exactly the same wiring was there but we
managed to charge the battery inside the smart doorbell yeah so the battery is there obviously to
keep the camera alive at night you might have some infrared infrared leds on there and at certain
times the camera may take more power than possibly the transformer itself could provide so it's got
its own sort of power reserve in there and then obviously compromises at the same time it has to
function like the old bell switch right okay yeah because it activates the bell charm we've already
got in the installation so not a lot of the work to do electrically but there's some really clever
stuff in here hence the rig you built should we take a closer look look so here's what we'll
have in a typical consumer unit we've got our bell transformer fed by an mcb 230 volts on the primary
side and eight volts at rated at one amp on the secondary side and that feeds along to our um
l that we've got here we've added a lamp as well we'll come to that in a minute and then down to
our switch we've also got a couple of points there for testing both the current and voltage across
the switch as well as the voltage across the belt yes just so we can see how this setup works and
then compare and contrast so here's my schematic which obviously we've got a collection of wires
on the bench but it really is a simple circuit out from the transformer down the bell down the
switch yeah very simple circuit almost possible that's why wonderful LS Lousy right so what you
can do first yeah so let's check the uh what happens in the conventional so press the button
no it rings yeah and we've added that lamp so if you're watching with the subtitles on
you can still enjoy the action that's going on okay so that's what we've conventionally got
in our property so you're going to measure some voltages for me now yeah let's just see what uh
what the operating voltages are in the system so let's have a look at the at the bell side first
well it's 28 volts isn't it well you'd think that gary you would but um what you find is these bell
transformers are really quite poorly regulated so unless you're loaded to the absolute maximum load
significantly higher than that on the transformers so we've gotten about what 12 13 volts there
weren't we yeah exactly okay so you're now going to measure the voltage across the switch yeah
so let's uh well let's just check that so there's the 15 volts that's the unloaded voltage from the
from the transformer yep but then obviously you'll also see there is now a voltage present across the
terminals of the switch yeah and opacity may have had a little incandescent lamp there to
illuminate the switch so you could see in the dark obviously that's because the uh obviously
the voltage flows through the tran through the um windings of the of the bell itself
okay
obviously when we push the switch because that's obviously closing the circuit will you measure
the current now for me yeah just see the current so again this is why we have this uh this problem
where the voltage is a lot higher than we'd expect obviously this transformer is rated up to an amp
right as we'll find out here we'll just see what sort of currents we're dealing with here
so again we're just setting the multimeter up to measure current
yeah it is okay so so that's what we conventionally got in an installation then
so you can introduce your smart Netatmo camera next yeah so here's uh yeah we're using
attack modes there's lots of similar uh similar devices on the market but we particularly like
this one check out the videos if you haven't seen that so again just removing our existing
switch and it's just simply two wires and we're going to use that voltage to power
our smart doorbell and charge a small battery in there that's required when it switches out
of circuit okay so it's just booting up there now yep oh oh you've got a problem gordon yeah that's
the first problem right okay so it's juddering the uh the bell and the the lamp is illuminated yeah
you can see there's a current flowing in the circuit and that's the current flowing to charge
the device up but again that's flowing through the windings of our bell down into the circuit but
what we've actually created is a sort of potential divider situation we've got some voltage across
the bell itself and the voltage across the switch so let's just take a little closer look at that so
i'm just going to take out that current loop that we put in there to do the measurements just insert
the but you're going to need that the actual uh attack mode because you can need to charge the
cell within it aren't you yeah so yes so there's current flowing but it's saying it's creating that
potential dividers remember that science lesson that you didn't pay attention in yeah i don't
know how to use it in action so let's just measure the voltage at various points of the circuit so
we're in that juddering position yeah so there's across uh so again this belt you know ah yeah
yeah it's almost at the eight volts we need that's rated at but we've also got
almost seven eight volts across the switch we're doing that potential divider
yeah it's because of the current flowing to charge the battery is obviously inducing uh obviously
the the bell to start working when it shouldn't be right so we're gonna actually obviously gonna have
to solve that problem what's this yeah so this is the chime module so this has got some really
clever electronics in it we're not we're not going exactly how that works at this stage um but let's
just do a little measurement on it so what you will notice is i'll just do that that's actually
just put the leads on we're going to measure its resistance is that yeah switch the resistance and
you'll see it's a law resistance connection across those two wires okay and what we do is we put that
across the bell so essentially we're almost almost shorting the bell out in the circuit
and what is this to get rid of that juddering sound it's going to correct it but this doesn't
say this device is clever so imagine now so it's a very low resistance at the moment yeah
there's some settings on there that for different bell setups but this is the most common one
right okay so you're backing you measure the voltage again is it yep so again so okay
right so that's yeah yeah so yeah one and a half volts across the the the bell at the moment okay
so let's settle down so what we've got there so yeah about yeah one and a half volts right
okay across the the belt yeah so now i'm going to just uh trigger the belt right okay so with that
voltage change well hopefully again but remember we're shorting out the circuit with the switch
at the bottom yeah fully working and we've got 12 volts earlier on across bell so what's happening
there then so that device when it's uh when the bell is pushed it's switching itself out of
circuit ah that makes sense so it's in circuit to get rid of the juddering but when pressed it pulls
itself out to allow the voltage to go across the belt yeah now that's clever that is clever
through the switch so again the switch is uh yeah essentially going to a very low voltage and then
back up to you can see they've got 10 volts across the device when it's when it's in-circuit because
it's having to charge that battery yeah but again it's changed the ratio in that potential divider
network that we had earlier so like with any good lesson in order that learning has occurred
i've got to explain what happened then we're in for some trouble i would suggest here
so the chime module is connected across the bell and then that's sometimes in circuit and
sometimes out of circuit so when it's in and connected it's actually bypassing the bell and
taking the electrical energy down to charge the smart doorbell is that correct yeah that's right
when i press the smart doorbell button i want the power now to actually energize the chime mechanism
so in that case it switches itself out of circuit allowing the bell to ring yeah that's it and and
uh yeah we had a we had a little look inside this before we made a video to actually find out
ourselves what's going on in there and essentially what you've got in there is a solid state relay
that does that that switching process plus obviously a lot of electronics to understand
when to switch the relay out of circuit and when to bring it back in and just to remember
obviously we've set it on the sort of default mode that Netatmo recommend there are some other modes
depending upon um different bell configurations that you may have in circuit so if we put it in
its standard mode and we still found we had chattering that's when we start changing it
from one to two and then over from low to high yes yeah okay and that changes doesn't it change the
resistance of the resistance yeah there is some of the high resistance modes in there as well now
obviously we've looked at the netatmo version here there's lots of smart doorbells on the market and
we believe some of those modules work in different ways so if you if you want if there's a different
way on the one that you've installed and you've figured out how it works then yeah please put
those comments below on that the other problem gary yeah that we found you may have noticed that
our eight volt transformer wasn't outputting eight volts it was generous it gave us nearly 15 volts
didn't it yeah and that's the other problem you've got when you're installing smart doorbells that
you're trying to add something to a circuit that perhaps wasn't initially designed to have smart
electronics fitted to it and therefore you have to fit in with what's there before and that obviously
changes by manufacturer or by different types of bell and even by the wiring now we yeah it's
been a while since i've fitted a doorbell but it would suggest that the wire supplied these
kits has got a lot thinner than it perhaps used to be in the past yeah so we got 15 volts out
of something we expected to get eight volts out of you've got another bell transformer here which has
got different tap off points and you've got it set at zero to eight volts so if i bring in the camera
should we see what that's going to give us so zero to eight there yeah yep so across our first tap
you can see that one's getting eight volts yeah well eleven eleven and a bit so again generously
you always expect on the transformer the the voltage to be high when they're unloaded yes
um so again let's have a look at the 12 volt tap on there one second so we've got 16 16 volts yes
and then across on our 25 volt tap we've got 28 volts and that's what that electronics is
fighting against isn't it to regulate that voltage yeah now obviously the the bell transformer in our
previous version that's not very well regulated at all almost double the output obviously in
a no-load condition and this one's actually yeah seems to have done a slightly better job
but remember obviously there's the transform in the circuit the bell itself this one here we found
about 0.3 amps when it was drawn we did try this on another on a classic ding dong type doorbell
and we found actually we could even get the circuit to work without the chime module in place
and obviously that's down to the parameters of the bell we don't suggest you try and fit them
without the chime module but again that's a yeah you don't know when you go up the project or you
actually need to replace the bell transformer and what voltage is getting out what's the cabling
like and yeah obviously on a long cable run if you're a long way from the consumer unit yeah so
so we found an incredibly smart camera really easy to install but actually again it's the technology
in that time module that got us out of jail wasn't it it was that brilliant piece of technology
across the bell that allowed the camera to charge the battery or the doorbell to actually charge
wasn't it yeah so as always we're interested in your comments what smart doorbells are you
currently fitting have you fitted this one from natapmo and how did you find it this chime module
what's your feedback on that remember be kind in the comments help others who've got problems
be a community and we're trying to build one here on efix and please leave those comments below