World's smallest lightbulb flasher? Flashing Light Prize 2017-----make money online

today on Applied Science I'd like to

show you my entry for the 2017 flashing

lights prize this is kind of a fun

contest where people get to come up with

creative and unusual ways to flash an

incandescent light bulb so this is my

entry and I think it is potentially the

smallest self-contained incandescent

flashing light ever built it's very

small as you can see this is my thumb

and the light bulb itself is actually

from a model makers store so if you

build doll houses or model railroad you

might want a light bulb that is of scale

size right so super tiny and empowering

it from an SR 416 silver oxide battery

and the flashing circuit is just a

Schmitt trigger inverter with a resistor

and a capacitor so it's really the

smallest simplest thing that I could

come up with and that was sort of my

idea for this entry you can hear a fan

running in the background and what that

is it's actually a heat gun so here's

the nozzle of the heat gun that I'm

waving at the device and the trick is

that we're pulling so much current out

of that poor little SR 416 coin cell

that it needs to be pretty warm to

deliver enough current to power the

incandescent light bulb it's about 12

milliamps just to get visible light at

all and the light bulb itself is rated

for 15 Billy amps at 1.5 volts so what I

do is I have the heat gun set on pretty

low and every minute or so I just wave

the heat gun at it to make sure that

battery stays it you know maybe 30 or 40

degrees see when I first built this

circuit I tried powering you know

powering it just from the coin cell that

had been sitting on the shelf and it

just barely worked I would say it didn't

really work so we're right at the limit

of what we can get out of that battery

and conveniently it's just enough to

light up the smallest of the

model-makers bulbs so they had slightly

larger one so I can get one in the frame

here this is a what they call a micro

bulb so even for model makers this one

is pretty small but as you can see the

one that I'm lighting up here is a

cylinder shaped

old and you can get them even smaller so

that's 750 micron in diameter okay let's

take a look at the individual components

that make this thing work the six lead

device is our inverter it's actually a

single inverter so it has power ground

in and out and two of the pins are not

used and then we have an O two O one

capacitor and an O two O one resistor

and the convenient thing about using O

201 with this particular package is that

the lead spacing is just about right so

that you can put this on here and

without even a piece of wire was just a

blob of solder we can connect this up in

fact what I needed to do is make one go

diagonally and the other part go between

leads and the spacing is just about

right to make this work then we have the

bulb itself this is the 0.75 millimeter

tube shaped light bulb tungsten filament

bulb and the SR 416 battery I'll put

links to all this stuff in the

description by the way you can see that

I attached a piece of magnet wire to the

battery with a spot weld so actually

don't have the spot welder here to show

you this right now but it's basically a

capacitive discharge machine so what I

do is you can see where I put one probe

goes here and the other probe goes on

top of the wire before it's welded of

course and then I press a foot pedal and

it sends about 10 joules of energy very

quickly through that joint and it welds

the copper wire to the steel case of the

battery the fact that it's capacitive

discharge is good because the current

happens or the flow of current is so

quick that it doesn't have time to cook

the whole battery before it welds the

thing in place although I have quite a

bit of experience welding wires to tiny

coin cells and the SR 416 being

essentially the smallest coin cell you

can get has a really thin metal case so

thin that if you put about 20 or 30

joules of energy into the spot weld it

actually ruptures the case pretty

reliably so you can really only get by

with about 10 joules of spot-weld energy

let's take a look at the test setup that

I use to build this circuit so on the

left you can see the flashing light

there and it's

connected to the same six lead package

on the right it's just taped down to

that piece of wood there and using

larger parts just to make it easier to

swap values in and out and I've got a

really nice power supply they're

supplying 1.5 volts to the whole thing

and I'm supplying the power through a 10

ohm resistor to simulate the battery

internal resistance and a power supply

as measuring total power going in and

then we've got the scope measuring the

voltages on the input/output and the

power supply of the inverter so it took

a little bit of tweaking to get all this

working and this was before I discovered

that warming the battery up just 10

degrees C improves its characteristics

quite a bit okay here's the circuit

pretty basic here's how it works so if

we turn this thing on and it happens to

start up success that this node is at 0

volts then the inverter inverts that

into full power or full voltage and

let's say we're running at 1.5 volts so

the output is now 1.5 volts so this

capacitor will get charged up heading up

towards 1.5 volt through this resistor

so the time constant between the

resistor and capacitor what determine

how long that will take

obviously if the resistor is smaller it

will charge up this capacitor more

quickly and if the capacitor is smaller

it will take less time so it really

really rounds numbers the frequency that

you'll get is about 1 divided by RC and

in this case we've got 2.2 micro here

and half a million here so multiplying

those together is about 1 + 1 over 1 is

1 so that the frequency of the circuit

is about 1 Hertz and that's pretty close

I think I was measuring on the scope

that it's more like 600 really hurts or

something like that but it really rounds

numbers that's what it is you can see

what will happen when this when the

cycle continues so let's say we're

charging at this cap and we get up to

the transition point here then the

output suddenly goes low and so now it's

discharging this cap through the

resistor and the cycle continues now the

trick is that we definitely need this

inverter to be a Schmitt trigger

inverter if it's not a Schmitt trigger

that means that there is some input

voltage for which this will be a stable

circuit so if you tried to build this in

it word and it wasn't a Schmitt trigger

you might get one or two

oscillations out of it but what will

happen is eventually the input will

reach the switching voltage let's just

pretend it's 0.75 volts the output will

then become 0.75 at some point in time

and then the end point is 0.75 and

everything is stable and the thing won't

oscillate so the trick with a

trigger is that the switching point

changes depending what the output is so

if the output is high that means the

switching point is suddenly quite a bit

lower than it used to be it's a type of

positive feedback or hysteresis on the

oscilloscope you can see that the yellow

trace is the output here and that's

moving up and down very drastically

which is good because we want our light

bulb to flash on and off you know

definitely to have nice sharp

transitions but then this node over here

is the purple trace on the oscilloscope

so you can see that that node between

the resistor and the capacitor is

varying voltage slowly over time as it's

charging and discharging the capacitor

and then the green trace is monitoring

the voltage supply to this whole circuit

so to simulate the battery internal

resistance on powering this whole thing

through a 10 ohm resistor and then

monitoring the voltage drop on the

circuit side of that 10 ohm resistor and

we're dropping maybe a couple of tenths

of a volts I also characterize these

tiny light bulbs to better understand

how I could build a circuit around them

and one cool thing we can do with this

power supply is sweep the voltage while

measuring the current to get a really

good understanding of what this light

bulb is going to do so we can instruct

this thing to generate a voltage sweep

linear let's say starting at zero volts

and going to 1.5 and it's going to step

up and we can set a current limit just

to make sure it doesn't blow something

up step once and so we'll generate all

this and then we can press trigger and

what's happening is it's stepping the

voltage up slowly and measuring the

current and so then if we check out the

graph of what just happened we can see

starting at zero volts of course zero

current and as it gets up to about 1.5

volts it's doing you know 15 milliamps

just like it says on the package

so let me run that again and this time

as it's turning on so right now it's

generating visible light so it's it's

easier to see by doing this kind of a

few times but if you watch the LED and

the graph at the same time right where

this thing starts to bend there's

there's a sort of a discontinuity in the

resistance of this thing and the light

bulb will start generating usable light

right around here right around ten

milliamps where there's sort of a step

change in the resistance of the bulb so

you know if this is current dependent on

voltage the slope of the line is

actually the resistance of the thing

that we're measuring and when the bulb

is cold it has pretty much a constant

resistance and then there's this

transition point and it changes into a

different resistance they're kind of

interesting so no matter what you do you

can't really get into useable light by

giving this thing less than ten

milliamps let's say just because you're

rewriting in this different region

originally when I started designing the

circuit I thought there might be

something really clever that I could do

with a MOSFET to try to make an

oscillator without even a shim it

trigger inverter to make it even simpler

and just do it with untransparent quite

get it to work in my research I found

there are certain weird types of

transistors that might be built into

oscillators but in this case I was

thinking maybe I could be tricky and

used the gate capacitance of the MOSFET

and the source resistance of the battery

to make some kind of an oscillator or

use the fact that the voltage will dip

when it switches and then try to get the

MOSFET to switch back into the other

state or something anyway I poked at it

for a while and didn't get very far so

my challenge to you is to make an

oscillator even simpler than this one

okay see you next time bye

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