A ucontroller story from another forum - Your opinion

[whiz115]

Hi

long time no see and also long post... (if you want.. you can jump to capital letters text and then
to the bold ones).


for the ones who happen not to remember my id i'm an old member but i rarely login
anymore because for some time i keep a distance from soldering irons and pcbs..

the reason i'm back today it's because lately with all this ARM uC "revolution" i thought it
might be interesting to see what are they capable to do in contrast with the ones i was
somewhat familiar Pic16f628A, Atmega328

so i found a forum talking about the development board i bought the other day... and i joined
them with great enthusiasm!

So what's the problem you might ask? the problem is that i started doing threads about
this that and the other, asking help so i can choose and start an interesting project.

...and here goes what happend!

among many ideas i had, (such as building an MP3 player etc), i typed one tiny magic
sentence:

"can i make this uC to do FM transmission?"

initially i got a warning from a forum member that i shouldn't ask that question
it wont go well and --at the very least-- the topic will be locked and he gave me the link
of a similar thread which was locked after a similar question.

and then 3 members and one moderator jumped into the thread started blaming me
that i am contempt for laws and regulations because i replied that an FM transmission
in your private place which is only few meters long can't be illegal (never was) and in
fact all these years small FM transmitters were sold at electronics shops either online
or in the physical stores and also jack plug to FM transmitters for the car are sold up
to today everywhere.

after that they started to reply to me in capital letters and the moderator told me

ANYONE WHO TRIES TO BUILD A DIGITAL FM TRANSMITTER IS LIABLE FOR
JAIL SENTENCE AS DIGITAL SIGNAL EMIT SQUARE WAVES WHICH DOESN'T EMIT
ONLY TO THE BASE FREQUENCY BUT TO ALL IT'S ODD HARMONICS. SQUARE WAVES
EMIT HARMONICS INTO AVIONIC AND MILITARY BANDS!

then i asked who does these things on this thread? and i was blamed that i was about
to do! although i don't even know how to program my uC since i'm a beginner on
this programming language.

and now i wanna ask...where's Nigel to say his opinion? because these guys i was talking
they were English nationality and also they had the language fluency advantage!! what's
going on there in England Nigel?

Audioguru is around? i remember once he has posted his tiny battery powered FM transmitter
and helped whomever wanted to build it to experiment with.

first thing to say, if i'm not wrong every transmitter and (not only square wave ones) if there
are no filters can transmit to neighbor frequencies and it's harmonics can be strong enough
depending how close you're, right?

also i wanna ask, how much power can a microcontroller 3v3 I/O pin output at 12-15mA?
still after all these years i haven't managed to become an electronics master but i think
the RF power can't be more than 50mW, which is enough for a couple of meters
transmission... how many meters does anyone knows exactly?

with that power if you want to extend the range you need to build an amplifier with
many gain stages so you can get a usable power output, the design of an RF pcb can
be tricky and needs experience, is that right??

also why somebody who wants to build an FM transmitter for broadcasting (and not for
experiment) to choose a device which isn't capable of sinusoidal signal as it normally
should? what's the point?

does anyone knows a project called "tempest for eliza" http://www.erikyyy.de/tempest/
it's too old and it was about using a CRT monitor's electromagnetic field to do
AM modulation and receive in your radio.

smart project and proved that for years we were living inside electromagnetic fields
in our homes which extend enough meters, has anyone tried it ever?

such electronics experiments were legal to do at your home? or illegal and we
should never learn how far our devices emit electromagnetic waves?


i really got disappointed and kinda lost my interest to do soon any project with the uC.
why? because it wasn't just one person with not friendly behavior if it was just one
person i could think it's just his / her view about it.

 

[rjenkinsgb]

Certainly a rather bad approach, but the warnings themselves were valid.

the RF power can't be more than 50mW

That is exactly 1,000,000 times higher than the UK power limit for such "audio sender" type devices and 500,000 times higher than the US limit; 50 nanowatts and 100 nanowatts respectively.

FM transmitter (personal device) - Wikipedia

en.wikipedia.org

You would be amazed how far radio signals can travel at extreme low power levels - there is a type of Amateur (Ham) Radio called "QRP", dedicated to getting the longest distance communications using very low power.

Some example records are 1650 miles using one microwatt and transatlantic communications with 78mW
They were using "short wave" band, on around 30 and 15 MHz respectively; it would not work on the broadcast FM band due to differences in propagation.


There is nothing to stop you experimenting as you wish, as long as you do not deliberately transmit!

 

[JimB]

for the ones who happen not to remember my id i'm an old member but i rarely login
anymore

I remember you, welcome back.

"can i make this uC to do FM transmission?"

Yes it is possible, I saw an article somewhere describing how to do it.

My own opinion is "that is dirty!"
The signal was generated at some lower frequency, and the radio was receiving a harmonic in the FM band.
But the micro was also generating other harmonic signals up and down the radio spectrum. A very anti social thing to do, also illegal.

ANYONE WHO TRIES TO BUILD A DIGITAL FM TRANSMITTER IS LIABLE FOR
JAIL SENTENCE AS DIGITAL SIGNAL EMIT SQUARE WAVES WHICH DOESN'T EMIT
ONLY TO THE BASE FREQUENCY BUT TO ALL IT'S ODD HARMONICS. SQUARE WAVES
EMIT HARMONICS INTO AVIONIC AND MILITARY BANDS!

Yes, illegal.
But jail time? Most unlikely unless you persist in doing it after being told to stop.

first thing to say..if i'm not wrong every trasmitter and (not only square wave ones) if there
are no filters can transmit to neibour frequencies and it's harmonics can be strong enough
depending how close you're right?

Yes, a correctly designed transmitter will have filters to ensure that only the wanted signal is coupled into the antenna.

also i wanna ask...how much power can a microcontroller 3v3 I/O pin output at 12-15mA?
still after all these years i haven't managed to become master at electronics but i think
the RF power can't be more than 50mW, which is enough for a couple of meters
transmission... how many meters does anyone knows exactly?

The power output of such a system will be low, it is difficult to be precise without a lot more information.
But 50 mW can go a long way, more that a couple of metres, a lot depends on what type of antenna it is connected to.

There are many badly designed (ie cheap) digital devices and switching power supplies for things like LED lighting which cause widespread interference to radio systems.

such electronics experiments were legal to do at your home? or illegal and we
should never learn how far our devices emit electromagnetic waves?

Experiments on the bench with transmitters connected into a non-radiating dummy load are not a problem.
Or milliwatt devices, such as your FMing micro processor with just a few cm of wire for an antenna may not be a big problem.

As I type I see that rjenkinsgb is saying much the same as myself.

JimB

 

[whiz115]

hi

so we end up to what conclusion?

they took facts and then they started to bullying me although they knew i don't
have the coding skills to do that (if i had the skills needed i wouldn't ask if i can do such a project).

i've seen on youtube that even the ones who were able to do such project using C/C++ with other
devices they only used a peace of wire connected in one of the pins, so even for them who know much
more seems it had no real purpose to do a more extensive project and present it.


JimB i really would like to know how much RF power such thing can output the max 50mW i said
it's just a rough assumption multiplying the pin voltage output 3.3V and the current 12-15mA.
as i said these projects from what i've seen on youtube are done with a simple wire as antenna.


so what shall i do? say sorry to them that i even dared to ask if i could use an uC as a short distance
FM transmitter? and then go on with my questions on my projects?

 

[Nigel Goodwin]

hi

so we end up to what conclusion?

I suspect you already know the answer?, you're wanting to do something illegal, the only issue is they were somewhat OTT about it.

In the UK use of an illegal transmitter can be a serious offence, with unlimited fines and possible jail time - but extreme penalties would only be applied to extreme offences (and probably not even then).

Bear in mind your poorly made transmitter could take out air traffic control, emergency services, all kinds of things.

 

[whiz115]

Bear in mind your poorly made transmitter could take out air traffic control, emergency services, all kinds of things.

Hi Nigel

how are you? Audioguru is around here too? you mean the hypothetical transmitter...right? because i needed instructions
and code so i could built it.

and is a uC with a wire as an antenna on one of it's pins that strong to do all these? take out air traffic control and
emergency services?

seriously i'm asking as if i am back to the basics, without taking into account what i know or believe about it.

i don't forget that you and Audioguru of course (also other members too such as Ericgibbs) helped me with my
first steps on electronics, Audioguru taught me some basic RF.

 

[Nigel Goodwin]

Hi Nigel

how are you? Audioguru is around here too? you mean the hypothetical transmitter...right? because i needed instructions
and code so i could built it.

and is a uC with with a wire as an antenna on one of it's pins that strong to do all these? take out air traffic control and
emergency services?

It's amazing how far small power can go.

 

[Buk]

One wonders what your application is for a FM transmitter?

Especially as bluetooth chips and SoCs are cheap as chips.

 

[whiz115]

One wonders what your application is for a FM transmitter?

Especially as bluetooth chips and SoCs are cheap as chips.

there's no application, you program it to do that, you see it works
you learn some stuff on coding and you go on...

what application can have an uC outputting FM square RF while
if you really want to do something with FM transmission there are better
ways to do?

is that right?



Has anyone seen (or knows..) somebody's project called "Tempest of eliza" i posted link earlier?
this is in fact an AM oscillator you can nicely broadcast to an AM radio and play songs
the range is only limited by the CRT's electromagnetic power emission.

in that case what's the difference between building a tiny oscillator by yourself
or modulating the signal of one that normaly exists at your home??

 

[JimB]

@JimB i really would like to know how much RF power such thing can output the max 50mW i said
it's just a rough assumption multiplying the pin voltage output 3.3V and the current 12-15mA.
as i said these projects from what i've seen on youtube are done with a simple wire as antenna.

This is not a simple thing, but try this:

Let us assume that the 3.3v peak to peak signal is a sine wave (ie one single frequency), the RMS value of that sine wave will be

3.3/(2 x 1.414) = 1.17v (the '2' converts peak to peak into peak value, the 1.414 covberts peak value into RMS value).

To find the amount of RF power delivered to a load such as an antenna, we need to know the impedance of that antenna.
To make an easy calculation, lets us assume that the load is a simple dummy load with a fixed 50 Ohm impedance.

Power = VxV/R = 1.17 x 1.17 / 50 = 0.027 Watts ie 27mW

The feed impedance of real world antennas varies with frequency and the type of antenna.

A half wave dipole has a feed impedance of 75 Ohms

A quarter wave vertical antenna, above a flat ground plane has a feed impedance of about 35 Ohms.
The ground plane may be built as four horizontal rods, one quarter wavelength long at the frequency of interest.

We can change the feed impedance of the quarter wave vertical antenna to 50 Ohms by simply bending the ground plane rods downwards at an angle of 45 degrees.

The antenna which you described as

projects from what i've seen on youtube are done with a simple wire as antenna

such an antenna does not have a well defined feed impedance, we could measure it with suitable equipment, but just one piece of wire without some defined other piece of wire as a ground plane, is difficult to define its feed impedance.

Does this help?

JimB

 

[whiz115]

Power = VxV/R = 1.17 x 1.17 / 50 = 0.027 Watts ie 27mW

Does this help?

JimB

that helps a lot to improve my knowledge on RF matters and also for the case i described.

my raugh calculation said ~50mW your more precise says ~27mW

i assume the wire impedance results from the length the diameter and the frequency and
that's why it's hard to make a precise calculation?


i don't know if 27mW experimental FM transmitter should be a legal issue..
i think Nigel says it could be if it happens to affect avionic or military bands.


our old CRT monitors AM modulated by that little program in the link
how far you think it could go?

 

[Nigel Goodwin]

i don't know if 27mW experimental FM transmitter should be a legal issue..

There's no such thing as an 'experimental' transmitter, it's an illegal transmitter, as simple as that. The 'experimental' rubbish is by those trying to excuse their illegal actions.

 

[whiz115]

There's no such thing as an 'experimental' transmitter, it's an illegal transmitter, as simple as that. The 'experimental' rubbish is by those trying to excuse their illegal actions.

i want to read Audioguru's opinion about that.. can somebody invite him? i can't do cuz i don't think he remembers me..

 

[Nigel Goodwin]

i want to read Audioguru's opinion about that.. can somebody invite him?

If he wants to respond he'll pop up, but there's really nothing to say - illegal is illegal - how did your 'experimental bank robbery' go

Just sticking 'experimental' in front of something doesn't affect it's legality.

 

[rjenkinsgb]

i don't know if 27mW experimental FM transmitter should be a legal issue..

OFCOM say it is:

Rules on using radio equipment

The rules that apply to spectrum use in the UK. Includes licence-exempt use and devices like jammers and repeaters.

www.ofcom.org.uk

It's all set in statute law.

Wireless Telegraphy Act 2006

An Act to consolidate enactments about wireless telegraphy.

www.legislation.gov.uk

 

[whiz115]

[My reply doesn't mean i disagree with anything written here.]

just i wanna talk about it..

law is a law ok and seems something has changed lately concerning these matters cuz i never heard here or anywhere else that restrictions apply for such a low power fm oscillators and certainly there were sold at local stores all these years and still do (the ones for the car to play mp3 to FM).

but i wanna ask again.. what about the project in the link above?

The guy who did that program in the link picks that carrier frequency the monitor emits and modulates it and shows that short range electromagnetic emitions at various frequencies exist around us anyway.

isnt this exactly as if you built a small AM transmitter?

every time we used our TV or computer monitor wasnt doing interference at the AM band? how far that signal could go? if the signal from a toy FM oscillator can be an issue?

and don't forget i was bullied in the other forum just asking about if it is possible to do uC to FM

Bullying, or Cyberbullying or mobbing? (what term could i use? or none fits the specific case?) genarally though.. that is also can be a serious crime no matter the form it takes.

there are local laws and international laws and ofc EU laws about such behaviour even for trivial cases its unacceptable and its social barden so to say the least.

dont take me wrong alright? we just make a talk, also no hard feelings for the guys at the other forum after all now... they are trying to help me learn the uC and find interesting projects to do.

 

[rjenkinsgb]

Things changed drastically some years back when the "EMC Directive" was introduced to law.

That means no general products should be sold that emitted stray EM radiation at a level sufficient to affect any other general equipment, including such as radio and TV receivers.

That's one of the things the "CE" mark rules cover - everything must be certified compliant with the EMC directive.

It would (or should) need some extremely specialised equipment to pick up stray signals at any significant distance from present type computer monitors etc.

Even back when I took my Amateur licence exam (1978), a good section of it was on stray emissions & possible interference, to ensure you complied with the regs when building your own equipment or antennas.


Many things emit radio signals in most homes, but they should only be from equipment that complies with the various regulations, which means generally specific frequency bands with set power limits in each, and all items CE compliant (or "Type approved" in the UK) so they will not interfere with any broadcast or protected service.
(The signal limits are often based on "ERP", effective radiated power, device power multiplied by aerial gain).

There is no protection against interference with with other types of device operating in the same band - as with such as 2.4GHz WiFi, Bluetooth, video senders, microwave ovens and model remote control systems all operating in the same 2.4GHz band.


There are many "unlicensed" bands which you can use, if you buy the appropriate type-approved devices or radio modules, some of which have quite high power levels - 500mW on some frequencies, if I remember right?

As an example, these are not quite that powerful, 100mW out and claiming a 16Km range between two devices:

https://docs.rs-online.com/a6d4/0900766b8154402f.pdf

 

[whiz115]

that's right.. we agree although i didnt knew about this new EMC directive, because im not into these things..

nice that they are trying to control stray electromagnetic emission although i doubt they can, can they?
always there will be stray electromagnetic emission..

every type can be considered stray i.e your neibour's routers which are next wall or above you or bellow taken all channels and interfere with your router's signal quality.

 

[JimB]

what about the project in the link above?

The guy who did that program in the link picks that carrier frequency the monitor emits and modulates it and shows that short range electromagnetic emitions at various frequencies exist around us anyway.

isnt this exactly as if you built a small AM transmitter?

Yes and no.
The guy in the link was relying on the incidental short range emissions from the monitor.
Inside the monitor are many circuits with various frequencies on various bits of wire, and yes they will radiate to some extent.
The case of the monitor is not well screened and so some of the emissions will escape "into the wild".

In days gone by, television sets had quite powerful oscillators running at 15 or 16kHz to provide the line scan and the EHT. The waveform out of these oscillators was a sawtooth, and so was rich in harmonics.
Listening on am AM receiver on long or medium wave it was easy to tell if next door had their TV switched on.

None of these are intentional radiators and so get past the regulation.
But there are limits even for such things, in Europe (including the UK) the EMC directive defines what is and isn't allowed.

how far that signal could go? if the signal from a toy FM oscillator can be an issue?

I think I said earlier, a simple low power oscillator, on the bench, is unlikely to be a problem.
Connecting that oscillator to an amplifier and an antenna could very quickly become a big problem, especially if you do not know if the oscillator/amplifier combo is spectrally pure.

Going back to your microprocessor FM "transmitter", It is unlikely that it would be able to generate a 100MHz signal directly, but would generate the signal at a lower frequency, such that a receiver would be able to detect one of the harmonics.

As a demonstration, I set my function generator to give a 3v p-p 5MHz square wave, seen here on the oscilloscope:

A reasonable square wave, the rise times look a bit slow, but good enough.

Now look on the spectrum analyser:

The thing spreads far and wide.
On well shaped square wave, we would expect to see the fundamental frequency and the odd order harmonic.
Here we also have a lot of even order harmonics.

If this were connected to an antenna, we would radiate signals at
5MHz, the fundamental
15, 25, 35, 45, MHz etc, the odd order harmonics
10, 20, 30, 40, etc MHz, the even order harmonics.

Which is why, in my first post, I referred to this technique of signal generation as "dirty".


JimB

 

[whiz115]

The thing spreads far and wide.
On well shaped square wave, we would expect to see the fundamental frequency and the odd order harmonic.
Here we also have a lot of even order harmonics.

If this were connected to an antenna, we would radiate signals at
5MHz, the fundamental
15, 25, 35, 45, MHz etc, the odd order harmonics
10, 20, 30, 40, etc MHz, the even order harmonics.

Which is why, in my first post, I referred to this technique of signal generation as "dirty".


JimB

you're great...you know that right?

although i know these concepts i appreciate that you make it even more clear by showing a lab example.
what i'm not sure i know well it's the difference concerning harmonics from a sinusoidal and square.

if you can clarify that to me.

[edit]

earlier about the 27mW calculation you said the exact number also depends on the wire impedance right?

this results from the length the diameter and the frequency and that's why it's hard to make
a precise calculation?

every time getting online to ETO there's a ready class waiting and electronics lessons are given for the welcome back!