RF Module

[dhouston]

Is there any way we can make our own RF modules from basic components and maybe a PIC?
Here in Bangalore, India, there is no one who sells RF modules...
So has some one tried making RF modules???

It really depends on the frequency you want to use but ASK RF transmitters, in general and with frequencies below 500MHz are fairly easy. You can find schematics on the web. RF receivers are a bit more difficult but you can find schematics for superregenerative receivers also. In the past, Ming had schematics for both their ASK transmitters and receivers (~300MHz) online.

Unless there are import issues, you can also buy them readily online from vendors in Asia and Australia (as well as elsewhere). Futurlec, in Australia, stocks the same Wen Shing (Taiwan) modules available from many vendors around the world.

[shahidali55]

I need a simple design , in the 433Mhz range.
I searched a lot on google but couldn't find anything ...
I can buy it from an international vendor, but, the problem is the delivery charges are like two times the cost of the modules itself...
If i get a schematic i will be able to make it for a really cheap price as i will not mind using standard components...
I think the commercial modules avaible online are costly because they use SMD components...

[shahidali55]

I found these schematics on the net for the ming TX-99 and ming RX-99 modules...
The only problem is that in the TX schematic the values of L1, L2, C1, C2 and C3 are not given...
Could someone help me out???

[dhouston]

http://jap.hu/electronic/rf/el9805.pdf

[Melanie]

Your Transmitter Diagram (mxmit) is unsuitable for UHF due to poor stability in that design, the data-rate will be very slow (eg 300 baud), with a very short range (only a few metres), and create large amounts of inter-modulation product that will almost certainly be well out-of-band (it will NEVER pass any form of approval), however the general frequency will be determined by the formula...

f=1/(2 x pi x (rt (L1 x (C2 + C3))))

where

f = frequency in Hertz
pi = 3.141592
rt = square root of 2
L1 is the value of L1 from your circuit in Henries
C2 + C3 is the combined value of C2 + C3 from your circuit in Farads

You will have to do two calculations... one with C3 at minimum value, and another with C3 at maximum value, and that will determine your tuning range.

[dhouston]

Melanie,

As much as I hate to disagree with you, I'm afraid I must. X-10 has used that same basic transmitter design for about 25 years in all of their RF remotes sold in North America and they have passed FCC certification tests. You're right about the low data rate but it's fairly easy to get >100m range by using an efficient receiving antenna along with an MMIC wide-band preamp which costs less than $2. Out-of-the-box range is usually in the 10-15m zone.

In Europe, X-10 uses the same basic circuit (with exactly the same RF daughterboard) but with a SAW resonator and higher power since your regulations allow for much higher power but also have tighter frequency tolerances. I have no idea what the regulations may be in Pakistan.

I would have referred shahidali55 to some of X-10's designs on the FCC's online site but, a few years ago, they asked the FCC to block access to all their schematics. But I have attached the schematic to one of their universal remotes which I downloaded before they blocked access. I should also note that the North American versions like the attached use 310MHz.

[Melanie]

shahidali55 was talking about 433MHz... if you build that LC Oscillator circuit as shown, it'll move by several MHz if you approached it with your hand or finger (or even if it's damp or dry weather!!). Also, you're keying the Oscillator on/off with a square-wave (rich in harmonics), that alone would guarantee out-of-band radiation. Unless it's professionally built to extremely high tollerances with a lot of consideration to board layout, I'll stand by the comment it's unsuitable. A SAW resonator is a completely different ball game - but this isn't - it's a crude one-transistor LC Oscillator...

[dhouston]

I can buy it from an international vendor, but, the problem is the delivery charges are like two times the cost of the modules itself...

That's only true if you're trying to buy in very low quantities. I bought non-standard (i.e. the frequency is not one listed in their catalog and required different SAW resonators) 310MHz TWS-A type transmitters from Wen Shing in Taiwan for about $3 each in quantities of 100 pcs. Shipping charges were about $25 for air express to the USA. On the other hand, they wanted more than $5 each for the RWS-310 receivers (which are in their catalog) and I can buy an identical receiver (of better quality) made by another Taiwan firm from Mouser Electronics for $5 in single quantities.

There are several excellent application notes on the Linx Technologies website.

• http://www.linxtechnologies.com/inde...ection=support

RF Monolithics also used to have some good app notes but I haven't checked that lately.

• http://www.rfm.com

If you are looking for lower quantities I think you are still better off to buy the TWS-434A transmitter available from 20 or more vendors around the world. Even Velleman sells it.

If you haven't read it, the third page of the PDF I referenced earlier in the thread gives a schematic, with component values, for a SAW controlled 433.92MHz transmitter that uses pretty much the same circuit, merely replacing the LC frequency components with the SAW resonator.

[ra68gi]

Here in Bangalore, India, there is no one who sells RF modules...

Hi Shahid,
There are many vendors selling RF modules in India. Checkout these...
www.modielectronics.com (Chennai, Tamilnadu) or www.vegakitindia.com
I even found linxs tx,rx module capable of transmitting over long distances in Chennai.
www.rentron.com is another place with a lot of resource on rf modules.
Mr.Bruce who is a member of this form and also proprietor of Reynolds electronics (www.rentron.com) can help you on this subject.
Raghunathan.

[shahidali55]

Hello dhouston,
The file you posted (UR19A.PDF) has a nice transmitter schematic.
But, the complete details of L1 are not given.
Do you have a reciever schematic for this transmitter ???

[dhouston]

Hello dhouston,
The file you posted (UR19A.PDF) has a nice transmitter schematic.
But, the complete details of L1 are not given.

L1 is a circuit board trace that acts as the antenna. If you're going to build something, build the one in the http://jap.hu/electronic/rf/el9805.pdf link.

Do you have a reciever schematic for this transmitter ???

X-10's RR501 used almost exactly the same circuit as the Ming receiver for which you found a schematic. Or, you can do a Google search on "RR501 Orysh schematic".

The RF1 transmitter and receivers shown on the site cited by ra68gi http://www.modielectronics.com/RFPG_1.htm are the ones made by Wen Shing (or are clones thereof) that I mentioned earlier. You cannot go wrong with them.

OOOPS! The RF modules in both links from ra68gi are from HiMark (Taiwan). X-10 now uses similar HiMark modules in their latest interface (CM15A). As I recall, HiMark has schematics and parts lists on their website.

[shahidali55]

I finally found something on google that looks real easy to make.
Can someone tell me if these circuits will work and what range they might have?
http://www.cappels.org/dproj/LCRFLIN...tr/TRFxmtr.htm
http://www.cappels.org/dproj/LCRFLIN...rF/TRFrcvr.htm

[shahidali55]

Has anyone got any other ideas???
I just need a simple circuit that is capable of transmitting and recieving data.
Range - 25 to 30 metres...
Frequency - Anything . . .