AM transmitter for antique radios and other project updates-----make money online

today on Applied Science I thought we'd

talk about building AM radio

transmitters and then in the second half

of the video I'd like to show you the

upcoming projects on the channel which I

think you'll find interesting

but first a.m. if you restore antique am

radios as a hobby you've probably run

into this problem so after spending

hours getting the radio working you'll

find that it sounds terrible but it has

nothing to do with the radio the problem

is that AM broadcast just doesn't have

any good music on it and I thought that

in a sort of a major metro area there

would at least be one station that plays

old music but no so you know you could

just cut the speaker wires inside the

radio and put in hide an mp3 player in

there but that kind of defeats the whole

purpose of restoring the AM radio so in

my case I bought a 1938 Ford pickup

truck and it likely has the original

1938 radio in there and after a little

bit of work I got it working but like I

say there's just no stations and so what

we want to do is build a simple little

AM radio transmitter and then we can you

know broadcast decent music

to our own radio so here's the schematic

and the circuit built up on a perf board

just point-to-point wiring and the trick

here is that we have a 5 volt oscillator

but we're going to feed it 3.3 volts

from this regulator here and the idea is

that we can make the voltage go up and

down relative to 3.3 and the oscillator

won't burn out because it's a 5 volt

component but luckily it also keeps

oscillating when the voltage is lower

than 3.3 so at steady state let's say

there's no headphones connected to this

circuit we have 3.3 volts going through

the coil and will be a little bit of a

voltage drop here and then into the

oscillator and our output is just a 1

megahertz square wave at you know 3

volts let's say or 3.1 or something now

if we put an audio signal into the

transformer the impedance is matched

such that the headphone jack is

supplying a good amount of current

through this smaller winding of the

transformer and then we end up with a

much bigger voltage signal on the longer

winding of the transformer

so the current adds and subtracts to

what's already flowing through from this

DC supply and that's what gives us the

AC way of superimposed on top of the DC

there

okay so let's hear this thing in action

I'm just going to play some music from

the phone and as you can hear it

actually sounds pretty good I was

actually really impressed with the

fidelity and as it happens the matching

transform and everything just about have

the right levels so that this all works

out so the volume is pretty high on the

phone but it doesn't have to be

ridiculous and the amount of modulation

that we get into the am signal is is

about right I mean it's close and I'll

put the part numbers all this stuff in

the description if we look at the scope

the purple trace is the audio signal

going in from the headphones and the

yellow is the output from the oscillator

so we can see our carrier being

modulated by the audio here and if we do

a single and zoom in you can see the the

1 megahertz carrier there and if we kind

of scroll around you can kind of see the

carrier change height relative to the

audio signal that's going in so it's all

working fine oh I should also point out

yeah AM should not be a square wave

because we've got all kinds of harmonics

mixed in there but even still this is a

super hacky circuit and the fact that it

works so well with just three components

it's kind of its main feature okay so

that's all well and good but since this

is an automotive application what I

really want to happen is you know I get

in the truck and turn on the ignition

and good music starts coming out of the

radio without me fiddling with my phone

or plugging in an mp3 player queueing up

the music or whatever so I went

searching around for sort of built-in om

mp3 players and was surprised that these

are actually pretty common so this is

five dollars on eBay including shipping

from Asia and the remote five dollars I

mean it's crazy and so I got a couple of

these just to see what it's all about

and these are actually surprisingly good

you can put an SD card in here

or a thumb drive it even has an FM radio

in here too and it's a single chip and

its output is line out so originally I

tried connecting this to the previous

circuit thinking that it might have

enough power to drive like a headphone

style thing but it doesn't and so I'll

show you what I did to make this work I

also want to point out that one of the

main features of this thing is that when

power is applied to it it automatically

starts playing the last song that it was

that it was playing so if you have a

hundred mp3s on this SD card and you cut

power to it and then put power back on

it will pick up where it left off at the

beginning of that song so it basically

accomplishes everything I want with the

power switching on and off and starting

to play the music again

so I started probing the circuit and

found out that the two output lines it

has a left and right output that are

meant to be connected to your car's

amplifier and as I mentioned it's not

really a headphone jack output it's

actually a high impedance very weak

signal output so it won't work with our

previous transformer circuit so I traced

these back and it's actually just the

connections through C 22 and c-26 those

are the coupling capacitors and then it

goes right into the chip here so since

we since this thing doesn't output

enough total power to actually modulate

our one megahertz oscillator what we

need to do is add an active component to

amplify the amount of power in that

audio signal so that we can modulate our

amplifier and I did that with an op-amp

there's actually another nice convenient

little happenstance the whole circuit

here is a 3.3 volt circuit and that's

the 3.3 volt regulator there and the

chip is set up such that if you if you

tech or if you steal the audio signal

before it goes through those AC coupling

capacitors it is centered on about 1.6

volts DC and the audio signal swings you

know about a volt or something like that

around 1.6 volts DC or half a volt or

something like that so conveniently if

we add a voltage doubler to it with an

op-amp the

the baseline becomes 3.3 volts and we

have like a 1 volt or even

one-and-a-half audio signal superimposed

on top just like what we needed to

modulate to give to our oscillator to

get a decent AM signal out so that's

what I did set up an op-amp here and

since we don't have bipolar voltage

supplies I used a op-amp that can go

down to ground but this one happens not

to be a rail to rail opt amplifier so I

have I added a 5 volt regulator so we're

giving the op-amp 5 volts and then the

signal directly from the mp3 player chip

and it doubles that voltage and we just

put that right into the oscillator so

let's hear how that sounds ok I'm going

to apply 13 volts here simulating the

car's electrical system being turned on

and the thing boots up and accesses the

SD card that I've got in there and you

can see it's transmitting we turn our

radio up

sounds pretty good and the fact that it

has a little bit of like am sort of

characteristic noise on there is kind of

part of the whole point of doing this

right I mean if there's a little bit of

static and it's it should sound like an

AM radio basically so that is kind of

okay I'll zoom in here so you can see

what the box looks like okay so here we

are stealing the audio signal before the

output coupling capacitor and there's

our op-amp we're only using a quarter of

that chip this one happens to be an LM

324 but it really doesn't matter almost

any op-amp would work and then this

funny setup here I have two RCA jacks

and coupling this into the antenna

wiring for the car was kind of a little

bit of a challenge you can't just have

like a paper clip hanging out that

doesn't provide enough coupling to the

cars antenna so what I did is I cut the

coax going from the radio to the roof

antenna and put RCA jacks on it so I can

basically just slip this in line with

the car's antenna wiring and then if by

some miracle AM broadcast is you know

okay or worthwhile listening to again I

can just tune off of this station okay

and so then you can kind of see how this

whole thing looks here what I'll do is

mount this you know in a hidden location

in the truck cab maybe even underneath

the radio or something underneath and

that will actually allow me to use the

remote without this being visible or at

least kind of hidden under there so it's

a pretty stealth setup basically it's

just as if AM radio broadcast was worth

listening to it you know you just start

the car up and hey it sounds good

[Music]

okay so let's talk about some upcoming

projects on Applied Science ok project

number one I'm going to do a cable modem

teardown and talk about cam modulation

which is pretty interesting and I have a

whole bunch of test equipment from tech

that allow me to show cam really

interestingly and hopefully talk about

the firmware that's in this modem - I

was actually able to get some

interesting stuff out of it

okay project number two here we are at

the scanning electron microscope I

recently backed a couple Kickstarter's

they're going to let me do some really

interesting stuff with this I've got the

latest teensy from pulsed African and I

need some help with the high speed USB

interface on that so if anyone knows who

to talk to about that and much

appreciate it and I also backed the

Mehcad we know project which is a

low-cost servo motor project made by

tropical labs and so the idea here is

I've got three axes of servo motor and

I'm going to connect them up to the

controls the motion controls on the

scope and then do image acquisition with

the teensy while controlling the servos

so that I can make animations with the

SEM in a fully automated way and then

this guy is way faster than previous

teensy so I can do much better video

acquisition especially if you get

high-speed USB working okay speaking of

high-speed my friend David Cranston has

built this amazing high-speed camera and

we're going to be seeing a lot more

stuff with this in the future since this

happens to be completely wireless it's

battery powered what I want to do is put

that high-speed camera on a really

high-speed motion platform this one's

linear but I have some other ideas in

mind and then I can move the camera at

really high speeds while capturing

high-speed video and that should make

for some really interesting dynamic

shots

I've been collecting parts to make a

really high pressure chamber like a

hundred thousand psi pressure chamber

and you can do some pretty weird tricks

with that and so I've I got this gage

which even goes up to 150 thousand psi

and have also been buying these unusual

high-pressure fit

that are used in water jet cutters so

this thing's been kind of on the books

for a while but I think eventually we

are gonna get to this and try some

extreme pressure experiments I also have

plans to build a really powerful and

precise temperature control system so

these thermoelectric cooler units are

really common these days and what we can

do is put one on this off-the-shelf CPU

cooler if you haven't seen these is

actually a pretty good deal for what you

get it's like 60 bucks or something like

that and you get a prefilled radiator

system so that if you put the module

here it has a really good heat sink on

the other side and then the other half

of that project is a really powerful

beefy bipolar DC supply I should also

mention I've had some temperature

measurement equipment donated to my

channel which I haven't gotten to yet

but it would trust me it's coming and I

do appreciate the donation and finally I

have been working on the gecko tape idea

someone came up with a really really

great idea of anodizing aluminum to

create this porous structure and then

casting silicone into the porous alumina

and I've had some early experiments with

that nothing's quite worked out quite

yet but that's still in the works too

okay see you next time bye earn money online by clicking, online money income site, money earning sites, online earning sites, best website to earn money, free money earning sites, money earning websites, get money online, online earning tips, online earning without investment, earn money online without investment for students, earn money by clicking ads, earn money online without investment, online earn money website, online jobs to earn money, best online income site, top 10 online money earning sites, easy income online, easy online earning, earn money online from home, make money online legit, earn money online free fast and easy, online earning websites list, genuine online money earning sites, online work to earn money, online surveys to earn money, earn money through internet, best online income, earn money online data entry, easy ways to make money online, best online earning websites