I've spent many hours trying to figure this one out, and I need some help.

I am trying to find components which will allow me to have 8-12 transmitters that can each trigger a channel of an 8-12 channel receiver. I don't need to send any complex data, I just need the transmitters to each send a high or low signal (depending on the logic) to a multichannel receiver. To each output on the receiver I will hook up an LED. So if Tx1 is activated then Rxch1 will turn on the LED.

So far I have looked at RF and RC solutions, but mainly RF. So far I have found plenty of already-made Tx and Rx modules, but as I read into them, they won't do what I need them to do.

For example, this Tx/Rx combo is for one channel. This would be okay, too--it would not necessarily have to be 1 receiver. I could have one Rx module for each Tx module. I'd just install them next to each other. There's a problem with that, though. It seems that previously-linked-to combo would interfere with others in the close range I intend (Rx modules next to each other, Tx modules spread out within 150m radius, preferably farther). I asked two suppliers of these, and one told me they would interfere with each other, and one said they would work just fine. Who is correct?

Another solution I found is actually having a 12-channel receiver (here) with 12 transmitters (here). The Tx module is encoded by soldering a fixed code to the circuit (as in the picture on that page). Would this be a good option or will those Tx modules not work all at the same time?

Both of the above options are limited in distance. It'd be nice to transmit up to at least 300m. I've read about XBee modules that transmit/receive up to 1 mile, but those are more expensive.

Earlier I mentioned RC devices. I could use a multichannel RC Rx but I cannot seem to find any 1 channel Tx modules.

Thanks for any input.

 

I also noticed the use of encoders and decoders in these type of applications. My understanding is that this automatically encodes the output of the transmitter, but then would I have 12 decoders trying to accept that same signal? Or does the learning process change that?

 

I think you are over complicating things. Or confusing me.

How far are you transmitting? 300m?

Have you seen these:
http://www.rentron.com/PicBasic/RemoteControl.htm

Choose what you want send what you want. Unless you are trying to reinvent the wheel, this is pretty straight forward. Have a look at some of the products and read the datasheets. I think you will find it is much easier than you thought.

 

Yes, I have visited that website before. They have long-range receivers and transmitters for 3,000ft, but they are over my budget. I am trying to keep this project near as $100 as possible. I ultimately only need a 350-600 ft range.

I guess I just feel overwhelmed and excited to get this project finished.

I understand that a logic 1 on one end will simply transmit a logic 1 on the other, but I just do not know which modules to purchase. Will 12 transmitter modules, as long as they are the same frequency, be compatible with a 12-channel receiver to send that logic 1 to each corresponding channel?

On the rentron website, will the TWS-434A and RWS-434 work? I'd rather have 1-channel transmitters with multi-channel receivers though.

 

If the transmitters are all on the same frequency, you will have a huge traffic jam. You will only receive the signal from the nearest transmitter.

Ideally, you need one master station. The master station sends out an interrogation signal that is addressed to a unique transponder, one at a time. The transponders are slaves; they only "speak when spoken to". This means having receivers/transmitters at each site.

If you want to "go cheap", then you might get away with transmitting only extremely short bursts of information from each transmitter, but the likelihood of the reception being garbled is very high.

 

SgtWookie

That's what I thought (the traffic jam). However, what if only 1 transmitter sends a signal at a time?

I know RF ID tags and readers use transponders. Beyond that, I don't have much knowledge of how they work.

So if all 12 sets or Tx/Rx cannot be active at the same time (using the individual pieces), could I try to design a sort of state machine that cycles through powering up each Rx at a certain clocked rate? That way only one receiver would be active at a time. Some Tx modules shut off after 10 seconds of transmitting, so the cycle would have to be 833 mHz (10/12). When one detects a logic 1, it would latch an LED. Or is that way too complicated?

 

SgtWookie

That's what I thought (the traffic jam). However, what if only 1 transmitter sends a signal at a time?

Who's going to act as a traffic cop?

I know RF ID tags and readers use transponders. Beyond that, I don't have much knowledge of how they work.

So if all 12 sets or Tx/Rx cannot be active at the same time (using the individual pieces), could I try to design a sort of state machine that cycles through powering up each Rx at a certain clocked rate? That way only one receiver would be active at a time. Some Tx modules shut off after 10 seconds of transmitting, so the cycle would have to be 833 mHz (10/12). When one detects a logic 1, it would latch an LED. Or is that way too complicated?

I don't know what your requirements are, as far as reporting time. I don't know what the minimum cycle time is for the transmitters. If you have access to the transmitters as to the sequence of their power-up, why not just send the information down that same line instead of going to RF?

Am I missing something here?

 

Are you thinking you need 12 transmitters and receivers to send a 12bit word?

You only need 1 Tx/Rx at each end, and you can send data packets that are coded for which relay.
On the remote end, the data that is received can be read:

[ARE YOU THERE] (YES) [GOOD, STARTING TRANSMISSION]

[FOR UNIT 1] HIGH [END]
(RECEIVED: UNIT 1 HIGH)
[CORRECT]
[FOR UNIT 2] HIGH [END]
(RECEIVED: UNIT 2 HIGH)
etc, etc.

The circuit on the receiving end can route the highs and lows to where they are supposed to go by you transmitting on the same line, WHERE there supposed to go.

You only need one channel.

I used a form of error correction in the flow above, to reduce the chance that interference was received.

Just like a computer network, you send the computers IP address then the packet that goes to that computer. All on ONE channel. You can have many hundreds of computers on that channel listening for their IP then receiving, Ignore the rest.

 

I need 12 transmitters because I need each Tx to light up its own (1 of 12) LED on the Rx side. That's why I'm thinking I need 12 channels. The receiving end would ideally be something like this, but I'm just not sure what transmitters I can use for it.

My other option was having 12 separate Rx modules, and I suggested cycling through them just so they wouldn't crosstalk with the Tx modules all on the same frequency. I really was just throwing that idea out there.

 

I need 12 transmitters because I need each Tx to light up its own (1 of 12) LED on the Rx side.

no friend you dont.

You can do this with 1. Using a shift register on the RX side, you can fill in the 12 you want to display 1 at a time, then light the LEDs all at once (The ones that you want lit)

Of you have 12 LEDs You can hook each pin of a 12bit shift register to an led resistor combo.

You send the LED high or low for each led in order. When the 12th is recieved, the shift register dumps the 1 and 0 to the 12 leds.

So if you transmit:

1 1 1 0 0 0 0 0 0 0 0 1

After the last 1 is recieved
the leds will be sent the pulses corresponding to those pins

You can do this so fast, that no human eye will notice it is one at a time.

It is called persistence of vision.

Use a Serial in Parallel out shift register.

Serial in (One at a time in from the RX)
Parallel Out (All the led instructions will happen at once)

 

no friend you dont.

I don't what? I don't need 12 transmitters or I don't need 12 receivers.


I've used shift registers before to make counting circuits, and I understand the serialin/parallelout register as well, but the RF part of it I do not get.

I really do need 12 transmitters. They will be spread out away from each other to create a monitor-type system. When there is a change on one of the monitors, the transmitter just needs to light up an LED on the receiving end. If I had just one Tx the shift register would be fine, but would all 12 Txs be able to send to one receiver? I'm really not sure as to how that would work.

That would be very nice if each Tx sent in a contributing signal, say Tx 1 sends in a 1 and the others send in 0s. 1 0 0 0 0 0 0 0 0 0 0 0. Then one LED would light up. But could it even work that way?

In the situatino I'm designing this for there would likely be several minutes or more between each change, with only one Tx detecting a change at a time.

 

That would be very nice if each Tx sent in a contributing signal, say Tx 1 sends in a 1 and the others send in 0s. 1 0 0 0 0 0 0 0 0 0 0 0. Then one LED would light up. But could it even work that way?

Yes.

The What you do, is for every cycle, you light or dark each led. You send a status signal of the module each second or so.

The led lighting circuit on the reciever end, gets all 12 status bits in order and parallels them out to the leds.
So a 12 bit register has 12 output pins. LED 1 hooks to output pin1 LED2 to O/P pin 2 and so on to LED 12 to O/P pin 12.

The receiver circuit has to be a transceiver. It will say "Hey unit 1 how are you?"

And unit 1 will say "Good" (1) or "Bad" (0)

Then main unit will say "Hey unit 2, how are you?"
each response in fed into the shift register.
when the 12th response is fed in, the shift register parallels them out to the LEDs, displaying the lighted or darkened LEDs.

They could all be on the same channel.

They would all listen for the "Hey unit #" before it responds.

 

retched

That actually makes a lot of sense. So a transceiver is both a transmitter and a receiver. I haven't ever really looked into these, so I just did a quick search and found several transceivers that vary from 800MHz - 2.4 GHz. I really have no clue. What type of transceiver did you have in mind? And what kind of Txs would work with that?

 

You can just use transceivers. I didn't have any in mind, but I would use 13.

So 1 transceiver as home base and 12 transceivers in the other 12 areas.
Figure you may get a discount for buying 13.

 

Okay, is this what I need?

http://www.sparkfun.com/commerce/product_info.php?products_id=9582

or this?

http://www.sparkfun.com/commerce/product_info.php?products_id=9581

 

Either will do nicely.

 

I haven't worked with micro controllers yet, and, according to what I've read about transceivers, in order to apply them I'd need to program them with micro controllers. I may have to stick to separate transmitters and receivers.

 

Thats unfortunate. Now may be the time to get into them. There is alot of help here and on the rest of the In-tro-net.

At only a dollar or 2 each, they are a great way to reduce part counts in your circuits.

But, its your project.

 

Well, if I had the correct equipment to program them, would there be already-written firmware available by somebody on the Internet? I'm assuming this type of application is pretty common, so many people have done it, right?

 

RF Data transmission? yes. All over the place.

It really comes down to your budget and deadline.