R/F - with the most easy-to-get/cheap parts

[Xyz123]

Hi all

I wish to build the most simple R/F system, a transmitter and a reciever - BUT - it's always a problem for me to find and buy parts, because my electronics shop only sell the most common parts, TTL's and CMOS's, res's and cap's :,( hehe. And plus, I almost don't have any money at all.

That's my challange. Help?

 

[Nigel Goodwin]

For a start you need to give a lot more information?, such as what it's for?, what range, and what band it needs to be? - bearing in mind that licence free is VERY limited.

 

[RadioRon]

The simplest RF system of transmitter and receiver would be best done by a beginner at a low RF frequency, like 1.6MHz or so. In this case, you can build with very simple circuits including simple transistors like 2N3904 or 2N2222 and similar common types. These are usually available for very little money. Of course, you will need some inductors and they will probably have to be significant value inductors, like in the tens of millihenry range so you may have to do some scrounging for those. The resistors and capacitors don't have to be anything special, just try to use ceramic capacitors where-ever a low value (that is anything below 1 uF) is required. You can use breadboard construction on a blank scrap of pcb by cutting the copper areas using a knife or rotary grinder (ie. dremel). Do not use the solderless plug board for this type of project as the capacitance between the rows of connections is just too high for RF circuits like this.

You should find a transmitter schematic using a single transistor LC oscillator (not crystal controlled. At these low frequencies it is easier to use LC and suffer a bit of frequency drift) followed by an output amplifier using simple NPN or PNP transistors. Such a simple two transistor approach is fairly easy to build. You will probably want to modulate the carrier but we can't tell what you want to do so the choice of modulation is not clear. If you are just building for experience, then the easiest is to use AM modulation of your output amplifier using voice or music from an audio source. I recommend that you do the research to find some sample schematics in a library or similar place where books are kept. I would be happy to comment on which schematics are most appropriate once you have narrowed down the choices and show them to us here.

The nice thing about using such low frequencies is that you can debug your transmitter and see if it works using a common broadcast AM receiver at, say, 1.6MHz to start with. Once the transmitter is working, you can build the receiver and use the transmitter as a signal injector. The receiver is usually a bit more difficult, but this depends on how sensitive you want it to be which in turn depends on how far you want your little wireless system to reach. And this depends on what you are trying to do, so why not explain it to us a bit more, please?

RadioRon

 

[mramos1]

I have found a couple on the internet. I tried them once and they did not work (I was short on time and just tinkering). Google for simplest rf trasnmitter, and maybe single transistor.

Radio Ron. Do you have an single transistor transmitter and receivers in the 1.6Mhz range, that would do 100 feet line of sight? On a 9volt battery?

Not sure if this might be was Xyz123 is after.

 

[Xyz123]

thanks to all

My final purpose is to create a wireless inter IC communication for room control. Since i'm a totaly new to electronics, I thought I'de start with someting as simple as transmitting any degenerated "data", such as "blik-blik blik-blik" - to get my r/f learning curve over with :wink: , but, in the scope of minimalising time/effort/cost of my overall purpose, I'de be willing to bypass some espects in that curve

The market offers R/F modules that look extremely fun and easy, but are costly. So, I thought, R/F has been around for many many years, there must be a way for a person living in the year 2006 to build an extremly low cost R/F system for extremly low bitrates.

Have an extremly nice day

 

[mramos1]

I agree, but I never find a solution. Maybe this time. I do not like the cost as well.

I kow Nigel has a tutorial on signalling on his website (Manchester I think you want to look at).

I would like the same item as you to play in my yard, so my range is a little longer.. I can have micricontroller, beep beep X number of times to know what area of my yard has someone in it.. Probably be my cat though.

 

[Xyz123]

Url-me, please

 

[DirtyLude]

The radio modules I use are from radiotronix and they're $5.00 each from mouser.com, hooked up to one of the $2.00 lynx matched frequency antennas. I think that's about as cheap as they come.

www.radiotronix.com
www.mouser.com

I'm currently making a simple little remote for turning on/off my gas fireplace.

 

[mramos1]

That is Nigel's site.

 

[mramos1]

I will do look at the radiotronix. I figure that is $5 for each side (pair). And $2x2 for antenna... $15 will not break me..

I was hoping for a simple TX/RX 1 transistor myself, and use the uC to turn on and off to signal what unit I want or command to happen.

 

[Dan East]

I've never used these, but I hope to experiment sometime in the near future with them.

cc2500 transciever

Dan East

 

[RadioRon]

Those RF modules look relatively easy to apply. I note that the CC2500 is an integrated RF transceiver IC, but will be tricky to get working properly without a correct pcb layout to properly implement the output/antenna circuits and to provide low impedance bypasses. At 2.4 GHz you have to be careful to use well-designed transmission lines (like microstrip) and choose good quality SMD inductors and capacitors, preferably 0402 sizes. Such things are typically not easy for the beginner. That's why using an RF module like the radiotronix will be a lot easier and you are more likely to succeed at your ultimate goal which seems to be to get a signalling system to work.

If your goal is to learn RF, then a module won't get you very far because most of the work is done for you. But jumping into a 2.4GHz design for your first project is putting the cart before the horse. So go with the radiotronix modules if possible.

By the way, I would not use their antennas if I had little money. After all, it is very easy to make a quarter wave monopole antenna with a simple piece of wire correctly mounted on some metal. You could save yourself the $4 for the antennas if you don't care how they look.

In the meantime, I will look for an example RF transmitter and receiver design using very few transistors. I should have mentioned before, but the idea of using 1.6 MHz does have one major disadvantage. This is that it is hard to make a really good small antenna for this low frequency, so your range of communication will be quite limited and probably entirely dependent on how big an antenna you can fit. In fact, the best antenna may likely be a coil of wire of, say, about 20 mm diameter, mounted on your circuit board, instead of a wire sticking out of the box.

 

[mramos1]

RadioRon, I think this was the one I saw
**broken link removed**

I will have to dig for the receiver. it was 1 or 2 transistors. My problem, RF left my brain (or was lost) a long time ago. All the new "everything" in a chip will spoil you, and take a lot away from you.

Maybe I will order the radiotronix. See if they have transcievers for lost cost.

Xyz123: what did you end of with for a solution?

 

[Mike - K8LH]

The radio modules I use are from radiotronix and they're $5.00 each from mouser.com, hooked up to one of the $2.00 lynx matched frequency antennas. I think that's about as cheap as they come.

www.radiotronix.com
www.mouser.com

I'm currently making a simple little remote for turning on/off my gas fireplace.

Mark, which radiotronix module are you using (is there more than one)?

Regards, Mike

 

[DirtyLude]

Their one way low cost modules are here:
**broken link removed**

TX: RCT-433-AS $4.69 quantity 1
RX: RCR-433-RP $4.54 quantity 1

I've used the 315Mhz and the 433Mhz modules. I've tried to make my own antennas, but I've had little success doing so. I'm not certain if they are just very sensitive, or I just suck at it.

The microcontroller I use is 3.3v, so I'll probably order their 3v receiver next time. That's new, since I've looked last. Otherwise I have to run 2 reguators for 3.3v and 5v for the receiver. You can see a picture of a trasmitter and 1/4wave whip on one of my projects here:
**broken link removed**

The one thing I can say about the $2.00 antennas is that they look fairly professional if you have them sticking out of a project box. You can also get a 433Mhz SMD PCB antenna which looks nice. I have a couple, but have not tried them out.

You need to use some type of balanced encoding with these modules, if you want to transmit streaming data. Manchester or PWM or something. I use manchester encoding. I believe Nigels tutorials have something on this. There's also a sample PIC CCS C program on the radiotronix site that gives sample encoding/decoding.

 

[RadioRon]

Mramos, that one transistor transmitter is pretty cute. You have to admire circuits that are so frugal with parts. But I can see that it will have poor frequency stability, depending on what is moving around the antenna. This is because the antenna is tightly coupled to the oscillator and its impedance will partly determine, with the coil, what the frequency of oscillation is. Since this thing will likely oscillate at low VHF frequencies, I guess, the antenna impedance will vary if something moves nearby it (like within about 3 feet or so).

This may not be a problem for some applications but it means that the receiver will have to be fairly wide bandwidth to insure reception under all conditions. Wide bandwidth in a receiver means less sensitivity, and maybe less range, but then it can also be simple. Lots of tradeoffs to make!

 

[Xyz123]

what about Microchip's rfPic's?

 

[RadioRon]

Thanks for suggesting the microchip parts. I have not looked at those before so this was a good excuse to review some new parts.

The rfPIC series appears to be a very easy way to get a UHF transmitter. There are very few parts outside the PIC and with a bit of care, you should be able to make it work. The frequencies and powers available are suitable for a short range wireless one-way link, the same kind of range that you would get from a good garage-door opener, maybe a bit more depending on how good your antennas are.

For the matching receiver, I looked at rfRXD0420/0920. This part is not so simple to implement, but within the capabilities of someone who is determined and follows the advice in the datasheet very closely. For chips like this, it is essential (I mean really critical!) that you use a good pcb layout. The chances of undesired oscillation or poor noise performance are quite high if the layout isn't right. For this reason, I recommend that you ask microchip for an example layout since I didn't see one on the data sheet. They usually have such a thing, so it is worth asking or looking through their site. Copy their example layout precisely and the chances of making it work are very good.

 

[Nigel Goodwin]

I looked the rfPIC's a few years ago, I thought they looked rather complicated, and required too many external components. Like you say, the receivers are even more complicated though.

In the end I decided to go with licence free radio modules, probably cheaper than an rfPIC solution?.

 

[RadioRon]

I agree that using modules is the way to go if you want it to work first time and reliably. Implementing a transmitter or receiver starting with a chip can be pretty frustrating for an RF novice without any instruments.

One other source of simple RF link hardware is one that I've used before, which is to recover the transmitter and receiver hardware from a scrap garage door opener. The receivers are usually pretty good, while the transmitter, which is the thing in the little pushbutton portable plastic case, is really simple. Of course, the data that this is designed to convey is usually one a few bits, which may not be much use.