Hi. Today we are going to use our genius to create a pranking device, one
that senses you passing by and creates a massive sound and light of an explosion
which is created by exploding something I figured is easiest.
I am not an explosive expert, but I've blown enough capacitors in my time.
If you apply a voltage higher than its rating, it will blow up
like so...
Oh not plugged in...
like so.
Awww #$&$@
HAAAAAA!
Of course, if I would be running it from the mains power, it will be dangerous.
So you must not repeat this, but it will make for a good educational video.
Now to switch the high voltage over the capacitor,
I'll be using a five volt relay.
I can connect the power through the switch to the capacitor
that is connected to the normally open contact of the relay.
So when I apply five volt to the relay coil, the switch closes and bang,
let's give it a try.
We just need to follow the relays data sheet now to connect the wires correctly.
#*^$%
Oh, it says bottom view.
I thought it was top view and connected the circuit to the normally closed contact
which connects to capacitor to high voltage right away.
Let's try it again. Okay.
All good.
Now, if we connect the five volt to the relay coil,
it should blow up
the hell...
when you want it to blow up, It doesn't blow up.
When you don't want it to blow up, it blows up.
What is going on?
OUCH! %#$^
The relay contact was welded short.
See, I thought because my capacitor was ten micro Farad, its impedance at 60 hertz
would be around 260 ohms switch at 120 volt AC would draw less than half an amp.
But that's wrong.
These capacitors behave kind of
like this, conducting much more current outside the rated voltage.
So although my relay is rated for two amps when the capacitor blows,
it draws a lot of current fusing the relay contacts short.
So the first time I accidentally connected it to normally
closed contacts, they were already fused and when I flinged it, I broke it open.
So I guess after every use I'll have to fling the relay
to make sure the contacts are not fused or pick a higher rated relay.
Eh, I'll just fling it!
Now, I need a sensor and for that
I pick this photo cell or photo resistor
which basically changes its resistance based on the amount of light it receives.
The plan is if somebody passes casting a shadow on the sensor,
we want to detect it, switch the relay and bam.
So I placed the follow, as
you saw in series with another resistor between the five volt supply.
This is a voltage divider
which creates an output proportional to the resistance values.
So this voltage changes as the amount of light changes.
I placed these on my brand new breadboard
that comes with three power supplies and two voltage and current meters.
These are parts of a bundle I put together with Circuit Specialists to provide
electronic enthusiasts with some good low cost equipment to start their journey.
I'll explain it more at the end if you need one.
Now you see the voltage is changing
and instead of a fixed resistor I'm using a potentiometer because this way
I can change the threshold between shadow
and light based on the room lighting.
Now I fit the voltage into a BJT transistor, and
because the transistor might be drawing too much current from its base
and effect the voltage reading here and effect the gain,
I place two transistors in this configuration called Darlington.
I explained to you in my ElectroBOOM 101, one how BJT transistors work.
Go watch that one afterwards.
Fortunately, nothing went wrong in that one,
so it didn't get many views.
But I'm
putting my life on the line in this one, so you better like and subscribe now.
But basically the collector current is much larger than the base currents
by a factor of beta, which for my transistor is around 200.
But in this Darlington configuration, the two transistors together function
like one transistor with their overall beta equal to the product
of each transistor beta which will be very large, like 400,000,
and the base-emitter on voltage would be around 1.4 volts.
Okay, now the circuit is together.
We tune it with the potentiometer.
You hear it?
Okay, let's
connect the capacitor to the circuit.
Okay, good, good.
The circuit is off, the light is on, so it's not going to blow up
at the beginning.
AHHHH $%)#^$
[Anger, frustration and urge to break something]
Oh, the photo cell resistance reduces with light,
so it pulls the voltage up, turning the transistor and relay on.
But in my application I need the switch to be off when there is light,
which means instead of normally open, I should be connecting
to normally closed contact.
AWWWWW!
[Cries in sad charged particles...]
Oh right.
Well, if the five volt supply is off, the relay won't switch and stays on
normally closed at the beginning even if there is light and the capacitor blows.
So I have to connect it back to normally open contact
but switch the place of the photo resistor and potentiometer.
Now when there is light photo cell resistance is low, pulling the base
voltage down, keeping the transistor off until someone casts
a shadow on the sensor, raising the resistance and base voltage,
turning the transistor and relay on and bang.
[relay clicking on and off]
BANG!
[CHEERS OF JOY!]
My relay died.
Have to pick a stronger relay.
This relay can do 40 to 60 amps,
but I have to run the circuit on 12 volts, which is fine.
Let's turn the circuit into something usable.
I'm going to solder all these onto a board first.
You know, I think it is safer to add an LED to the circuit as well.
So we know when the relay is switching the live voltage to the capacitor.
[singing] Always look on the bright side of life...
Like so I'm using two alligator clips to hold the capacitor
so it's easier to replace and reload and I added an LCD too.
Now I'm sure everyone can find
an old wall adapter in their old stash of wall adapters.
I have this 12 volt one and we cut this open.
Now we have access to both the 12 volt supply and 120 volt contacts.
So we solder our circuit on.
[singing] Life is a piece of $^#@, when you look at it!!!
And what a beautiful product.
Let's try it.
Also for added accuracy, I put a cone around a sensor
so it's more directional towards a certain light.
First we plug the circuit in without a capacitor to tune it.
With the sensor pointing to the light.
We tune the potentiometer until it just turns off
like this.
See?
It switches!!
Now that it is off and safe, we place the
capacitor, OOOH $%@$, damn it.
PHEW!
Good thing I put the LED in to tell me when the circuit is on.
So we unplug it first, put the capacitor in,
then plug it back in...
OOOAAAAHHHH
#!&^$
@*$@
#@%^&$
This project is hell.
Okay, so we plug it in without blocking
the light.
Okay.
Okay,
#*%$&
HARUMPH
@%^*&
%@&$%%
[PIAN... SUFFERING... and general “why are we still here” vibes]
Piece of #%&*@$
Well, at least I hope you learned some electronics.
Just remember you can always start at safe levels with these tools.
For a long time I was thinking it would be nice
if there was a bundle of basic electronic tools and components
I could offer to people so they could start on their electronic journey easily.
And now there is Circuit Specialists and I put together a great bundle
that includes a large breadboard that includes two variable
power supplies with embedded voltage and current meters,
a whole lot of basic electronic components to play with,
a ton of jumper wires cut for breadboard,
a digital multimeter,
And a few... ElectroBOOM stickers??
which are very important for...
your circuits won't work without them.
And the whole kit is only 200 USD and is available globally.
Just that.
If you buy it from outside US, you will probably be slapped
with some import fees and duties, but it is still a good price.
So get it from the link in the description.
We can use these together in my ElectroBOOM
101 series to learn about electronics or you can get it
as a gift for someone who loves to play with electronics.
Do it now!!!
don’t click away yet! WatcH tILl tHE eNd!!!