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
- 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 receievers available if you follow all of the link here->
Kits of bits that might be adapted are avaialbe from
Have a look at zeevo, and Atmel's offerings.
I am sure I would, If I had the faintest idea where to start.
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.
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...
- Dan
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.
no, but mchip does make an rfpic line, which may be what we are seeing here.
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.
the board is laying flat on the background.
More information... I found good photo of the back of the board:
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
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.
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?
Dunno what that is for tho?
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...
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...:-)
Fellows,
I may be all wet, but the above web site shows the rfPIC's and the function says transmitter. NOT RECEIVER that you are discussing!
Just an observation....
Dan Thompson (AMA 32873, EAA 60974, WB4GUK, GROL) remove POST in address for email
so figure it out mr genius.. who pissed in your cornflakes
quite unnecessary, i never made any claims to greatness, just made some observations that obviously pissed you off somehow.
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...
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
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.
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?together"
impossible... I
pretty deaf,
Why would anyone want to design a model airplane, when you can just go out and buy an ARF? ;-)
-tih
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.
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.
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