# Microcontroller Based RC Receiver Project

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#### Daniel Rubin

Jan 1, 1970
0
Hello,

I have been doing some digging to find some information needed to
start a new project to build a RC (radio control) FM modulation
receiver for use with 72 MHz aircraft frequencies based on one of the
new PIC nanowatt chips. I have come up with very little on the
subject. Has anyone run across any relevent articles in the web or in
this list that may help me? An example of an existing product can be
found at http://www.slowfly.com/DetailPages/rffs100.html. Any ideas?

- Dan

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#### The Natural Philosopher

Jan 1, 1970
0
Daniel said:
Hello,

I have been doing some digging to find some information needed to
start a new project to build a RC (radio control) FM modulation
receiver for use with 72 MHz aircraft frequencies based on one of the
new PIC nanowatt chips. I have come up with very little on the
subject. Has anyone run across any relevent articles in the web or in
this list that may help me? An example of an existing product can be
found at http://www.slowfly.com/DetailPages/rffs100.html. Any ideas?

- Dan

I can't see how a microcontroller can be used to build a receiver, altho
of course it would make a fine intelliegent decoder and ESC.

What you need is access to coils, crystals, ceramic filters and probably
a good sweep generator and spectrum analyser.

If its of any help to you, there are a few schematics of 35/40Mhz DIY
http://www.norcim.fsnet.co.uk/#U and you could probably cahnge to &2Mhz
by simply using a different Xtal and a change to the two front-end RF
stage coils, and the trap coil. IF would be unchange.

Kits of bits that might be adapted are avaialbe from

Good luck!

D

#### Dave VanHorn

Jan 1, 1970
0
I can't see how a microcontroller can be used to build a receiver, altho
of course it would make a fine intelliegent decoder and ESC.

Have a look at zeevo, and Atmel's offerings.

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#### The Natural Philosopher

Jan 1, 1970
0
Dave said:
Have a look at zeevo, and Atmel's offerings.

I am sure I would, If I had the faintest idea where to start.

T

#### The Natural Philosopher

Jan 1, 1970
0
Dave said:
Sorry, I thought it was fairly obvious.

http://www.zeevo.com/
Zeevo does bluetooth at 2.5GHz on a single chip, and they do work quite
nicely.

http://www.atmel.com
You have to drill into products, communication IC's.

Yerrs, but those are not microcontrollers. They are specialised analogue
IC's. And designed for short range high data rate transmission, not long
range low rate, which is what we want.

D

#### Daniel Rubin

Jan 1, 1970
0
It must be possible to use nothing but a PIC to detect and process the
incoming signal. If you look at this close-up of the RFFS-100 in the
link below you will see no coils. The crystal for the desired channel
connects directly to the PIC.

I have extensive experience programming the PIC and would love to play
around and try to build something similiar from scratch. I am lacking
on the RF side...

http://users.joplin.com/~bselman/rffs100.htm

Thanks
- Dan

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#### The Natural Philosopher

Jan 1, 1970
0
Daniel said:
It must be possible to use nothing but a PIC to detect and process the
incoming signal. If you look at this close-up of the RFFS-100 in the
link below you will see no coils. The crystal for the desired channel
connects directly to the PIC.

I have extensive experience programming the PIC and would love to play
around and try to build something similiar from scratch. I am lacking
on the RF side...

YOU cannot use a PIC to amplify low level RF, period.

That has many other components apart from the large IC, which may, ormay
not, be a PIC. a PIC talks high level digital signals, and maybe low
frequency high level analogue. You HAVE to have an anlogue circuit
somewhere. Using a microcontroller to synthesize the local ocsilllator
is possible, but you still need a front end and mixer of some sort, and
doing without some form of filtering there is dangerous in the extreme.

As far as that reciever goes, its a two IOC design with preset crustal
solderd in. Its not possible to see what IC'ds are used, but one is
probably an integrated RF/IF/detector/Mixer/oscillator chip, and the
other is probably a pic doing decode - instead of teh standard CMOS 4017 IC.

My guess is there are a few coils on the back, and probably a few
ceramic resonators.

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#### Dave VanHorn

Jan 1, 1970
0
no, but mchip does make an rfpic line, which may be what we are seeing here.
http://www.microchip.com/1000/pline/frequency/rfcats/rfpic/
That has many other components apart from the large IC, which may, ormay
not, be a PIC.

given that they talk about firmware for the pic on that page, immediately
below the picture, it seems rather likely.

a PIC talks high level digital signals, and maybe low
frequency high level analogue. You HAVE to have an anlogue circuit
somewhere. Using a microcontroller to synthesize the local ocsilllator
is possible, but you still need a front end and mixer of some sort, and
doing without some form of filtering there is dangerous in the extreme.

there are other ways to receive rf, than the lo/mixer approach.
As far as that reciever goes, its a two IOC design with preset crustal
solderd in. Its not possible to see what IC'ds are used, but one is
probably an integrated RF/IF/detector/Mixer/oscillator chip, and the
other is probably a pic doing decode - instead of teh standard CMOS 4017 IC.

My guess is there are a few coils on the back, and probably a few
ceramic resonators.

the board is laying flat on the background.

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#### Daniel Rubin

Jan 1, 1970
0
More information... I found good photo of the back of the board:

http://www.rcmicroflight.com/images/dec02/RFFS100_01.jpg

It appears the 16-pin chip in the photo of the front of the board that
is connected to the crystal is not a PIC. This must be one of those
"integrated RF/IF/detector/Mixer/oscillator" chips you mention below.
Does anyone have a part no. for something like this so I can find a
datasheet? That 8-pin chip on the front is a LTC1516 5v charge pump
DC/DC conv.

The PIC is the 8-pin chip on the back of the board and controls the
magnetic actuators. There are other chips on the back of the board,
but no coils or apparent resonators.

- Dan

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#### The Natural Philosopher

Jan 1, 1970
0
Dave said:
no, but mchip does make an rfpic line, which may be what we are seeing here.
http://www.microchip.com/1000/pline/frequency/rfcats/rfpic/

given that they talk about firmware for the pic on that page, immediately
below the picture, it seems rather likely.

a PIC talks high level digital signals, and maybe low

there are other ways to receive rf, than the lo/mixer approach.

Indeed, and I have built a few. Mostly they don't work as well, and none
use all digital technology.

You are making sweeping statements about a subject you clearly know a
little about. I am making sattements about a subject both studied and
got a masters in and did as a profession for many many years.

There ois no PIC in the world that I know of that can do anything useful
with an NBFM modulated signla at 72Mhz, and 2uV level buried in an RF
spectrim of sheer choos, without some sort of amplification, and some
basic filtering to get the other stiff out as well as boost teh wanted
stuff.

Even DSP's which are far more applicable, need to see signals that are
of a level they can digitise - which menas at least a 60dB boost, and
that again will need some form of out of band filtering, and AGC,
otherwise other strong signals will overload it.

Of course, with a DSP, once more or less digitised, its only software to
do a decent IF strip, detector and smart decoding. But you will still
need something at the frin tend to do teh initial amplification and
filtering.

the board is laying flat on the background.

Oh well. Perhaps there is another board.

However, if you know all about it, why don't you *** off and make a mint
out of sellng them instead of asking someone else how to do it?

T

#### The Natural Philosopher

Jan 1, 1970
0
Daniel said:
More information... I found good photo of the back of the board:

http://www.rcmicroflight.com/images/dec02/RFFS100_01.jpg

It appears the 16-pin chip in the photo of the front of the board that
is connected to the crystal is not a PIC. This must be one of those
"integrated RF/IF/detector/Mixer/oscillator" chips you mention below.
Does anyone have a part no. for something like this so I can find a
datasheet? That 8-pin chip on the front is a LTC1516 5v charge pump
DC/DC conv.

Dunno what that is for tho?

The PIC is the 8-pin chip on the back of the board and controls the
magnetic actuators. There are other chips on the back of the board,
but no coils or apparent resonators.

There have to be. For decent performance at least. At a pinch you can
use ceramic resonators to do everythiung beynbd teh mixer, but teh front
end? Well you COULD just stick an antenna straight into teh mixer, but
it would have vile alternate channel and out of band rejection, and
probably transmit illegal amounts of LO signals itself.

However, if one is producing a kit to sell to the gullible, who cares?

If you want a schematic of a decent DC receiver, look
here...http://www.norcim.fsnet.co.uk/Index_files/image017.jpg

Fr9om p[age http://www.norcim.fsnet.co.uk/#U

As you will see, this uses 4 coils in all, and 2 Xtals and 2 ceramic
resonators. Its not totally 'state of the art' but is a damned good
small dual conversion superhet design, and works very well.

It has been DEVELOPED to fix and address typical problems found in real
life situations. Not just thrown together as a project by one guy who
managed to get the prototype working once, in a screened room with a
transmitter 5 feet away...

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#### Dave VanHorn

Jan 1, 1970
0
You are making sweeping statements about a subject you clearly know a
little about. I am making sattements about a subject both studied and
got a masters in and did as a profession for many many years.

so figure it out mr genius.. who pissed in your cornflakes
However, if you know all about it, why don't you *** off and make a mint
out of sellng them instead of asking someone else how to do it?

quite unnecessary, i never made any claims to greatness, just made some
observations that obviously pissed you off somehow.

D

#### Daniel Rubin

Jan 1, 1970
0
This thread started out as a request for info... why it turned into a
flame fest I don't know?

I wanted to build a RC receiever "in my spare time". I wanted it to
be small and I knew it could be done because of the existing
commercial product called the RFFS-100 (links to photos where posted).
From the photos of the product I could see no visible coils or
obvious RF circuitry. Hence the initial question. I have found a lot
of good info on the subject. Thanks also for that receiver
schematic...

The Natural Philosopher said:
It has been DEVELOPED to fix and address typical problems found in real
life situations. Not just thrown together as a project by one guy who
managed to get the prototype working once, in a screened room with a
transmitter 5 feet away...

BTW...

The RFFS-100 has a range of 1000 ft., it is FCC certified and is being
used by 1000s of RC modelers right now. Hardly a "thrown together"
project? All of that with no visible coils? Must be impossible... I
might as well give up

- Dan

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#### Dave VanHorn

Jan 1, 1970
0
The RFFS-100 has a range of 1000 ft., it is FCC certified and is being
used by 1000s of RC modelers right now. Hardly a "thrown together"
project? All of that with no visible coils? Must be impossible... I
might as well give up

i think np woke up grumpy this week.

receiver design isn't simple, unless you're willing to compromise a lot.
for example, you -could- do a receiver using a tuned cavity, and pulsed
microwave transmitter on 10.525 or 24 ghz. pretty directional, pretty deaf,
and pretty wide open to interference, but also pretty simple.

engineering is the art of compromise.

J

#### Johnboy

Jan 1, 1970
0
Just out of curiosity, why would you want to build a receiver
when you can buy one that works perfect, is built by a
100 million dollar company, has 7 channels and only
costs $75.00? T #### Tom Ivar Helbekkmo Jan 1, 1970 0 Johnboy said: Just out of curiosity, why would you want to build a receiver when you can buy one that works perfect, is built by a 100 million dollar company, has 7 channels and only costs$75.00?

Why would anyone want to design a model airplane, when you can just go
out and buy an ARF? ;-)

-tih

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#### The Natural Philosopher

Jan 1, 1970
0
Dave said:
i think np woke up grumpy this week.

receiver design isn't simple, unless you're willing to compromise a lot.
for example, you -could- do a receiver using a tuned cavity, and pulsed
microwave transmitter on 10.525 or 24 ghz. pretty directional, pretty deaf,
and pretty wide open to interference, but also pretty simple.

My first receiver used 4 transistors, one RF coil, one RFC, and two
audio transformers.

The one I flew a lot that actually worked had one less audio transformer
and one more transistor.

27Mhz single channel stuff. would receibve just about anything within
1/2 Mhz from 27

So I built a 5W transmitter. I could fly anybody elses model with that,
and in fact used it to get someones futaba equipped model back when it
ran out of range on their 90mW tranny . Nobodies signal was stronger
than mine.

T

#### The Natural Philosopher

Jan 1, 1970
0
Johnboy said:
Just out of curiosity, why would you want to build a receiver
when you can buy one that works perfect, is built by a
100 million dollar company, has 7 channels and only
costs $75.00? Because you can build a better one for$50?

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#### Dave VanHorn

Jan 1, 1970
0
The Natural Philosopher said:
Because you can build a better one for \$50?

i'm not advocating this, i'm just discussing it.
but i wouldn't take on a project like this to save 25 bux.
i would do it to learn.

J

#### Johnboy

Jan 1, 1970
0
OK guys, lets go! I have tons of circuits already, but would
like to see something processor controlled. What do you have?

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