So I’ve been picking up a whole bunch of these motion sensitive night lights and performance
has been, let’s just say, it’s not been great and the battery life definitely isn’t the advertised
only charge four times a year. But I thought it might be interesting to try and hack one of these
and see if we can improve it. I do have a whole bunch of these nice radar motion sensors the
what are these the RC-WL0516. But let’s crack open one of these and see what’s inside. I’ve
got round ones and I’ve got oval ones so pretty interesting. So the tops just kind of pop off
so if you just give it a bit of a squeeze then then we’re in. So we have the the motion sensor
there is a mystery chip it’s a eight pin mystery chip they’ve removed any identifying marks there
is a light sensitive resistor here and here’s some charging circuitry. Now let’s pop this screw out
and see what’s underneath. Okay circuit board just comes out and we have a massive 350 milliamp hour
battery it’s tiny. There’s the actual PIR sensor there. Let’s take a photo of this and then we’ll
do our best big Clive impression and reverse engineer the circuit. So one moment let me just
get a photo. Now as always this video is sponsored by PCBWay. We’ve used them for a lot of PCBs now
and they’ve been great. There’s a link in the description. So it’s pretty simple it’s a single
layer board the positive side of the LEDs are all connected to the battery plus and then the
negative side of the LEDs are switched by our mystery chip down to battery minus. Now that’s
all there is to say about that bit of the circuitry. There’s no apparent current limiting
circuitry so at least I can’t see any. So here’s our mystery chip we have the PIR sensor and the
positive and the negative sides of that PR sensor go straight into our chip. There is a light
dependent resistor with R5 as its resistor divider and there’s a C3 decoupling capacitor.
Now over on the charging side we have a TP4054 there’s a 3.3k programming resistor so that gives
us around 300 milliamps charging and there’s an LED to indicate that charging is happening and
again we have a decoupling capacitor. So it’s a pretty basic circuit really not much to talk about.
So here’s my reverse engineered schematic so we have the charge controller IC with its programming
resistor 3.3k got the lithium cell got decoupling capacitor then we have our mystery chip so here’s
the LDR with its potential divider feeding into the chip the PIR sensor PIR plus and PIR minus
go straight into this IC and then we have the two switch pins that switch these LEDs on and off so
here’s all the LEDs they’ll get switched down to ground so it’s pretty simple really highly
optimized in terms of BOM. So this mystery IC is obviously quite specialized for PIR sensors
and switching LEDs. So that was pretty interesting I am quite intrigued by the lack of any current
limiting on the LEDs so what I might do is hook this up to my bench supply and just see how much
current is being drawn we’ll do the current limiting so we don’t blow the LEDs up but
let’s take a look so let’s desolder the battery so that should be fairly straightforward.
Okay so it’s hooked up to my bench power supply ah there we go managed to trigger it so I’ve got
my current limit set to 100 milliamps currently drawing 68 milliamps so there’s definitely
some built-in current limiting on this mystery chip so anyway let’s have a play
with some of these nice motion sensors so we’ll move this out of the way
and I’ve wired a pin header onto this so now these can take a light dependent resistor as well
so somewhere in my bag of bits I have some light dependent resistors
okay got some light dependent resistors let’s zoom out a bit
so these are these are pretty interesting these light dependent resistors so I’ll
stick it in some red board here and we have around 2.6k at the moment when it’s in light
and if we cover it up yeah it’s gone up to 12 kilo ohms so 2.5, 12 so what we can do is we can
solder this light dependent resistor onto this board but let’s plug this in and have a play with
it you’ve got a flashing led let’s let’s get a normal led flashing’s a bit uh a bit silly uh one
second okay there we go nice solid red led now if we stay still it’s gone out if I move it goes on
it goes out now it stays on for around three seconds
now what you can do is on this board there is a space for a capacitor that you can solder on
yeah so on this side of the board this space here ctm if we put a capacitor across there
it will increase the time out so let me grab a little capacitor and we’ll see if we can increase
the time out because three seconds it’s not really enough time to get to the toilet so not ideal so
on off on
and then off so yeah so we’ll need to uh need to have a bit more time on that so
let me get a capacitor and fix that
nighttime mode activated needs to be very dark let’s just leave this to turn off
and then we’ll try again and check the motion detection does actually work
okay so we should be oh I moved and it came on so that’s working pretty well it is very sensitive
now apparently it is possible to solder a resistor on here and reduce the sensitivity but
we’ll try this out and see how well it works
so here’s the plan let’s just zoom out of it so I have a board here that I have
stripped of everything so I’ve removed the PIR sensor and the mystery chip and it’s supporting
components so what we’re going to do is we’re going to place this module somewhere around here
and then we’ll have a current limiting resistor and a MOSFET driven from the output so we’ll
probably put it around like this we’ll power it from the battery plus and minus
and um fingers crossed should work nicely let’s try soldering it up I will get the microscope out again
on the block selling data for a home scroll wars pixels pop battles in the streams they
pimp the ads out chasing digital dreams this ain’t no safe zone it’s the wild wild web got
me dodging subscriptions like bullets to the head almost subscribe but nah they can’t get me they
beat the hook but my wallet stays gritty they want my clicks my soul my pride but I’m too slick I
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I ain’t selling my hustle for a buffering dream almost subscribe but nah they can’t get me they
beat the hook but my wallet stays gritty they want my clicks my soul my pride but I’m too slick I
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so it’s actually come out much better than I expected and the board seems to be working
I put on a much bigger battery 820 milliamp hours um so let’s see if it slides back into its case
so put the battery in and then this just needs to slot in so that we can charge it without any
problem so I think I think that’s pretty good there’s the screw hole so let’s put the screw back
in and then the lid let’s say let’s put the diffuser back in just it looks like a normal one
we can can we do that there we go and then close the lid good as new so we’ll try this out later
I’ve mastered the ability of standing so incredibly still that I’ve become invisible to the eye