I am planning to build a small project involving 15 single button remotes. All remotes would be sending their signals to a single arduino. Question is what form of signal shall I use? It must be reliable and free of interference. RF? This project needs to be relatively inexpensive. These remotes will simply give the receiver its unique identity and the ardunio will do the rest of the work.

 

RF
Pre-made RF links, like Linx (http://www.linxtechnologies.com/).
Coded identifiers for each remote. See: Holtek. The Holtek chips were/are basically pre-programmed MCU's.

John

 

What sort of range is needed? Is it line of sight? How big/small do the remotes need to be?

 

The remotes don't have to be to small. preferably no larger then an iphone hopefully no higher then an inch high... (The the prototype may be a lot larger) They will be in line of sight with the exception of objects such as tables and chairs. The range should probably be around 5 meters. But do keep in mind that reliability is absolutely necessary.

 

Standard TV remotes are $5 or less if you watch the salesand each would have at least 15 buttons I think. So assign a different button to each user and you're done. You'll need an IR receiver module and then the software to decode the pulses. Problem: what happens when there are overlapping signals?

 

The signals sent when the button either pressed or released. The arduino should be able to receive and log them fast enough. Its hard to get an overlapping signal in milliseconds.

 

But do keep in mind that reliability is absolutely necessary.

Can you expand on that comment a little? What will happen if a remote sends a signal and the receiver doesn't recognize it as valid?

John

 

I'd recommend sending the code multiple times and with a different repetition rate and code for each transmitter.
If for example you have 2 transmitters pressed at the same time they could interfere with each other, but one transmitter repeats every 100ms and the other repeats every 150ms then it will always be possible to recieve both codes (assuming the code length is fairly short).
This is the method used for those IR controlled helicopters that you can fly 3 together.

 

This sounds like a wireless Jeopardy style game system. Is that you're project goal? IR is way too slow and subject to multiple-input interference. RF will probably require 15 TX/RX pairs at 15 different frequencies (not codes) to prevent single channel interference. I've seen many posts from people wanting to do it, but never seen one completed. I would be very interested if it can be done.

Ken

 

I hadn't thought of jeopardy. I did consider a couple of the Tx might step on each other, thus my question about recognizing a signal. Unless they are playing Final Jeopardy, I don't see why reliability is absolutely necessary.

My real concern was that this was going to be used in some sort of medical monitoring or life support device. If that is the case, I think it needs to be out in the open.

John

 

Can you expand on that comment a little? What will happen if a remote sends a signal and the receiver doesn't recognize it as valid?

John

That would be a problem. I don't see why it wouldn't see it as valid if the signal is reliable.

 

This sounds like a wireless Jeopardy style game system. Is that you're project goal? IR is way too slow and subject to multiple-input interference. RF will probably require 15 TX/RX pairs at 15 different frequencies (not codes) to prevent single channel interference. I've seen many posts from people wanting to do it, but never seen one completed. I would be very interested if it can be done.

Ken

My goal is much the same as you have suggested, yes.

 

I hadn't thought of jeopardy. I did consider a couple of the Tx might step on each other, thus my question about recognizing a signal. Unless they are playing Final Jeopardy, I don't see why reliability is absolutely necessary.

My real concern was that this was going to be used in some sort of medical monitoring or life support device. If that is the case, I think it needs to be out in the open.

John

No it is not a medical project at all. I had considered the possibility of the receiver only having to recognize the first remote but I think if possibility I would like to have them all recognized, even if it is a little more complicated or expensive.

 

I think KMoffett explained how a coded signal can be scrambled by another signal on the same frequency. That is why a lot of the chips for this sort of thing transmit the code twice. John

 

Are you looking for a pre-made solution to buy/use off the shelf, or something to build from scratch, including enclosures?

 

Are you looking for a pre-made solution to buy/use off the shelf, or something to build from scratch, including enclosures?

I would like to wip this whole thing up from scratch, unless a small pre-built circuit would make the remotes much simpler beyond what I could do myself. Project enclosures aren't extremely expensive, so they would be a possibility.

 

I think with your requirements, to "wip this whole thing up from scratch" will be impossible. There are a lot small Tx/Rx modules out there for not too much money. But, from what I see they are all based on single frequency, transmitted-code differentiation. Contacting some of the companies may prove me (happily) wrong.
Try LINX, or SparkFun, or Arduino... maybe others can make more suggestions.

Ken

 

The signals sent when the button either pressed or released. The arduino should be able to receive and log them fast enough. Its hard to get an overlapping signal in milliseconds.

The remotes I've seen keep sending the coded signal as long as the button is held down.

OP, is there anything wrong with the proposal to use multiple cheap IR remote transmitters? If you need absolute isolation of 15 channels with no risk of overlap, this becomes a more elaborate project by far.

I've seen bluetooth laser mice for under $15. Maybe you could use one central computer with 15 paired mice to act as clickers. Can BT be used with 15 simultaneous paired devices? Using a wireless router would allow the device number but then you'd need a b,g or n-enabled clicker. Not sure what that would be, other than an iPod, smartphone or a laptop.

 

The repeated mention of a standard remote being used for this project has got me thinking. I think the concept of the tv remote is absolutely brilliant and is exactly what I need if it can be adapted. I am looking for more of a finished product so the idea of hacking 15 different remotes to do the job is not necessarily what I had in mind. Although that could be used for prototyping. If anyone has anymore information or knowledge on how I could adapt the same concept I would be delighted.

 

Well, my idea didn't envision any alteration of the remotes. Just assign a different button to each user.

If you used programmable universal remotes (still very cheap), you might be able to find enough different device codes so that each remote issues a different pulse even when the SAME button is pressed. That'd make it a lot handier, if everyone could be told to use the "power" button, for instance. So one remote would think it's controlling a Sony and another remote a Panasonic, and so on. Still doesn't address overlap.