RF Controller With Limited Range

Hello,

I'm currently working on a project which requires a wireless signal to be transmitted over a range of roughly 2 to 40 meters. The application involves several receivers but only one within said range at any given time, and if the transmitter works over too large a distance there will be unwanted activation of the other receiving modules. I've been considering purchasing the standard 433 MHz RF transmitter/receiver module from the picaxe store. I lack any significant experience in the radio/wireless world, and the cost of these modules kind of prohibits me from my usual approach (experiment until I discover the correct hardware/configuration). Any direction would be greatly appreciated!

Welcome to the Picaxe Forum

First, let's clear up a few things that you may have preconceived.

1. With the proper BASIC code a receiver will not respond even if is in range. BASIC code can be written so that only the receiver you want will respond.
2. There is no such thing as a "standard" RF module. There are cheap ASK modules, commonly referred to as "dumb" modules, There there are FSK/GSK modules that have some intelligence since there is an micro-controller embedded in the module. These are usually transceivers that can both transmit & receive. There are many kinds & types of RF modules to chose from, but nothing is really standard.

To get started with RF stuff and you're "on the cheap", then get a pair of the cheap ASK modules from EBAY or elsewhere. These cost from $2.00 to $5.00 each. I also suggest you use PICAXE chips that supports the RFIN and RFOUT commands. These are either the 14M2, 18M2, 20M2, 28X2 or 40X2.

Please tell us what the project is and what Picaxe Chips you may already have and more help can be provided.

To expand on what Goeytex said in answer # 1, the picaxe can send a string to an RF transmitter which includes a "qualifier". Any (reasonable) number of picaxe receivers can look for different qualifiers, and only the one which matches responds. Then the picaxe can send a string with a different qualifier to talk to a different receiver. If there is to be handshaking because the system cannot afford to have a message missed, then other complications arise, which can be addressed at least partially with retries and timeouts.

RF reception can be so variable that I doubt you can rely on a receiver simply not hearing a transmission.

So far I've been working with 08M2 chips. I fully understand the programming side of things, more so just looking for some guidance with making the radio signal function the way I want. I should have been more clear about what I'm looking for. There is to be more than one transmitter as well, and I'd like to have it set up so that there would be no tuning to a particular receiver, just whichever would be in range. Anything outside of 50 m or so, and the transmission from one unit may interfere with the other. I understand that getting an exact range is impossible as it depends quite a bit on environmental conditions as well as hardware, but really anything under that 40-50 m would be more than adequate. The only transmitter/receiver I've looked at so far is the first under the circuit creator>miscellaneous section (433 MHz AM) which seems like it would fit my application quite nicely, but there is limited configuration information in the circuit creator section or any of the manuals; i.e. is an antenna necessary? If so what length? It states in the store that the operative range is 50 m, but is that at a certain power input and antenna configuration? I know some of these questions may seem painfully obvious but as I said I have no experience whatsoever with radio. Also, I wouldn't necessarily be "on the cheap" as long as I was sure whatever I was investing in would do what I needed. I suspect that the ASK variety is what I'd be looking for as I don't need the receivers to talk back at all. Thanks again for your time.

You are going to have to give us more details about the details.
As Goeytex has already explained, you can send a signal such that only the selected receiver will respond.
If you want to send a general broadcast that all the receivers (that are in range) will respond to, then you will need to learn and understand about radio waves / aerials because the size shape orientation and proximity to some materials will have huge effects on range.
Please explain in far more detail what your desired system needs to do.

If there is more than one Tx you may also have to worry about the case where an RX can 'see' two Tx at once.

If there a reasonable number of Rx, they could still be uniquely identified and the 'master' can poll through them, looking to see who is out there. That's assuming a two-way communication. Does your master(s) need to know this? Or will they blindly send data? Or is it simply a proximity detection thing at the Rx end?

When I tested dumb TX-RX pairs with two TX and one RX, the RX would lock onto one or the other of the signals and completely ignore the other, even whien the TX locked onto was moved further away than the one not locked onto. That may have been because of the way I was using them and it was a while ago so I cannot remember full details but I can foresee there being potential problems in reaching the desired goal in the way suggested.

The only similar project I could think of was tracking animals over a large area and the best way to do that would probably be using modules which are designed to co-exist on the same band with GPS, maximal range of transmission and multiple receivers to cover dead spots. Much like a building-wide Wi-Fi setup.

The only transmitter/receiver I've looked at so far is the first under the circuit creator>miscellaneous section (433 MHz AM) which seems like it would fit my application quite nicely, but there is limited configuration information in the circuit creator section or any of the manuals; i.e. is an antenna necessary? If so what length?

Click to expand...

These are dumb modules and as such there is no "configuration" to be done. All RF devices need an antenna. at 433.92 MHz, a 1/4 wave dipole can be a wire about 6.8 inches long.

I could be wrong, but I doubt that these dumb modules will be adequate for your application/requirements. We need more details. What exactly is the application? How many transmitters. How many receivers? How much data is being sent? What do the receivers do when they receive the data? Is the data sensitive? Will the TX or RX units be battery powered? Outdoor or indoor? Will there be obstructions such as trees or walls?

The more you give us, the more likely you will get good and relevant recommendations.

Alright I'll explain my project a little more in depth. I'm a farmer, and there's a certain crop that we have to harvest at night and load trucks "on the go" (not stopping to unload the harvester). Traditionally these trucks are directed forwards or backwards by a set of two wired light up arrows mounted on the harvester. At times these can be hard to see so my idea was to move the directional arrows into the truck and wirelessly transmit the forward/backward signal to those units. Selecting a specific receiver on the transmitter module wouldn't be ideal as it can be difficult to differentiate one truck from another at night. There are two harvesters in the field that generally don't get very close to one another, but if the transmitters were capable of say a kilometer that would cause issues. There really only needs to be three signals-forward, backward, and off. The terrain we work on is very flat and open with no obstacles. From the beginning I considered perhaps using IR to transmit but line of sight wouldn't necessarily be guaranteed so I scratched that idea.

I have used these radio units with a Picaxe to opperate a 30ft long Cable car model. So we could remotely turn in the base station motor, 3 Buttons on the remote, solder data in on to these....
The Rx box is 12v with latching relay outputs. With 12v terminals in them, It all opens up and you can solder directly too the PCB. And access radio Daughter board. All really simple inside. **50mtr range** you could measure and then cut 1/4 or 1/2 of its wave length of to bring the range down too your target range.
Each RX box can be programed too the relevant TX key fob that the picaxe sends via, each RX can remember 4 different TX units, or Just one TX..... etc

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