Help requested with 4KM long range 433MHZ RF Kit

Using Arduino Networking, Protocols, and Devices
1

Hello,

I recently purchased a few of these modules from ebay:

http://www.ebay.com/itm/4KM-Long-Range-RF-link-kits-with-encoder-and-decoder-/130545302887?pt=LH_DefaultDomain_0&hash=item1e651b3d67

I believe they are the same as the 2KM ones offered by seeed studio and others.

The problem is, these kits differ from the simple short range kits I have been using. The Tx has four output pins instead of 1, and the Rx has four input pins, as well as a "vt" pin, which indicates that a signal is present.

In addition, you must "pair" the Tx and Rx by soldering some pads on the back, which I have done.

I found a sample program here:

Which succeeds in sending data to the receiver "most" of the time. It iterates through the number 1 - 16, and send those numbers as bits. When the receiver detects a signal on it's "signal high" pin it prints the number. Some of the numbers work, some don't. There doesn't seem to be any connection between which number work and which don't.

I have tried just manually setting the pins high and low, but this doesn't seem to work.

I can't seem to figure out how these rf kits work, when compared to the simple 433mhz short range kits I was using.

I intend to use these kits with virtualwire if I can figure out how to use them.

I am nearly certain they work, since I am receiving good data some of the time, it just doesn't seem to work all of the time.

Has anyone out there used these kits, or has anyone got any idea where I might be going wrong?

Thanks!

2

Those kits use a encoder decoder chip , the sc2262 , sc2272 .
They arnt designed for sending hi speed data, but are more intended for simple on / off type functions where the data to be sent is very small and can be sent at a very low baud rate, such as garage door openers or Rf controlled wall switches.
They wont work with virtual wire , unless you somehow bypass the encoder decoder chips and just use the raw transmitter data input , and the raw receiver data output.
If you read the spec sheet on the encoder decoder chips , you should be able to work out what the maximum data rate is , but it will be very slow , less than 50 bps.

3

Ah, I see. I thought when it said "low data rate" it was something along the lines of a dial up modem speed. Not too worry, I was intending to use this as a remote control for a small robot anyway, so it should still work, I was just hoping to use virtual wire as well to send text strings.

Is there any way at all to get it to work without bypassing the encoder, if low speed isn't a problem? Or is it impossible?

Thanks for your reply.

4

Its possible , but the speed will be very slow.
The encoder / decoder chips can send data in 4 bit nibbles, so if you apply 4 bit data to the encoder inputs
they will be replicated at the decoder outputs.
The problem is that it takes anywhere from 100 ms to 1/2 a second for the data from the encoder to be replicated at the decoder.
In a noisy environment its even longer.
Its dependant on what clock rate the encoder chip is running at .
They simply use an RC oscillator and the data rate is set by an external resistor.
The data format used has a lot of overhead, which is primarily to make the link rugged and to prevent false data being produced on the decoder in a high noise environment, which is why they are slow.
The decoder chip has a Vt or data valid pin which indicates when the output data is valid, so if you keep your transmission rate sufficiently low so that the Vt pin stays high, you should be able to send low rate data OK.

5

What type of range have you been able to achieve with these ebay units and with what type of antenna & in what envioronment?

6

Hi JackStone:

Have you ever found the 433MHz kit met your demand?
What's the air data rate you need when working 4KM long range?
I

7

Folks,

Just as a side-bar ......

It should be clear to everyone buying the 433 MHz long range RF pair, that it was originally designed for a four-button priority switching remote controller. So for example, you can energize any combination of the four transmitter data pins and ONLY THE FIRST one pressed will go HIGH. All others will stay LOW. On the receiver side, the packet is shifted in to registry to match the four pins of the TX and will latch the packet in until the receiver detects all four bits of the incoming RF stream to be LOW. Only then will VT go HIGH and the new packet shifted in. Someone with more experience could correct me on the specifics.

So at any point, each packet will only contain ONE HIGH bit and the rest will be low. It should also be clear that this would not mesh well with virtual wire or any serial data scheme. You might warn your friends before they buy a set. Having said that, it has obvious value for the right application.