You could use keyfobs from several different cars, they are gotten from junkyards for cheap to free depending on if the battery is good or not.

They can then be converted to IR instead of RF by ripping out most of the circuit except the PCB buttons, add an LED, etc.

Most of a universal remote's size is the PC Board button area, you could try a couple brands to see if they could be cut up to fit inside each keyfob.

 

I don't think IR will ever work. The problem is near simultaneous responses. Try pointing two different brand remotes at your entertainment electronics stack. Push one button each remote near simultaneously. Likely nothing will happen. The IR decoder circuits see an overlapping mix of pulse codes strings that it can't decipher. The likely event would be that the last button to be released would score.

I did contact LINX about RF solutions. They have pairs of TX/Rx modules that can be DIP switch programmed for 8 different carrier frequencies, or others that can be serially programmed for 100.

http://www.linxtechnologies.com/Products/RF-Modules/HP3-Series-Multiple-Channel-Radio-Frequency-Module.

http://www.linxtechnologies.com/Documents/TXM-900-HP3-xxx_Data_Guide.pdf
http://www.linxtechnologies.com/Documents/RXM-900-HP3-xxx_Data_Guide.pdf

But...at about $50 per pair.

There may be others out there too.

Ken

 

RF will have the same problems as IR if run at the same frequency (IR is a frequency).

Would need some sort of spread spectrum Tx/Rx solution, and that gets a bit spendy with the number of remotes, especially for a single button push signal.

 

RF will have the same problems as IR if run at the same frequency (IR is a frequency).

That's why the links I posted are for modules that you can select 8 (or 100) different "carrier" frequencies, not just data codes on a single carrier frequency. If you were in a room with no lights, you could do the same thing with a bunch of emitters and detectors with 15 different narrow band optical filters from IR to UV.

And yes, they are spendy! That's my big limitation. If I were doing a commercial system that I rented out, I would do it in a minute. Return on inve$tment, you know.

Ken

 

KM- Thanks a lot I like your advice. RF is what I was thinking mainly but I do have a question. Would it be possible to have a receiver for each remote either RF or IR? The receivers size is not necessarily restricted so if necessary it could contain a separate receiver for each of the remotes. If this would be done would it be possible to use IR? Or is it to slow and pron to interference? The same question for RF.

 

The RF units would need to be 15 transmitters and 15 receivers. Each pair operating on a different frequency or RF channel. This not really possible for IR in the real world. My example of optical filters was just a whimsical comparison to the RF channels.

Ken

 

Light can be focused easily. Wouldn't 15 lasers give the same effect as different channels, if you had 15 receivers?

John

 

Interesting. How do those laser tag things work, as far as identifying who shot who?

 

Post #4:

They will be in line of sight with the exception of objects such as tables and chairs.

And maybe heads.

jarblue never spelled out the specific use, or other limitations of the environment. Lasers might work with individual receivers. There might be an issue of safety, even with low power pointers. And setup would be a a hassle. If they were table mounted, bumping the table would likely miss-align them. Just not enough info to go in that direction for me.

Ken

 

Light can be focused easily. Wouldn't 15 lasers give the same effect as different channels, if you had 15 receivers?

John

No sorry the laser idea is to fragile, not dependable enough.

 

I found this article to be quite interesting. I am wondering if this piece could be used for 15 different remotes.

 

Like I did with LINX, email them. This what I asked:

I'm looking into the possibility of making a wireless Jeopardy game style response system. Currently I'm using a wired system with 6 remote pushbuttons. The first button pushed locks out the others. In thinking about an RF option, it looks like multiple transmitters with individual data codes and one receiver would run into the problem of two transmitting simultaneously and interfering. Is it possible to get Tx/Rx pairs that transmit on several (maybe up to 16?) different frequencies, similar to the technique in R/C model airplanes and cars?

Let us know what they say.

Ken

 

So, is there some reason to NOT use bluetooth?

 

So, is there some reason to NOT use bluetooth?

I'm not familiar enough with Bluetooth. Ease of implementation for a single pushbutton, multi-frequency transmitters/receivers? Range? Cost?

Ken

 

I'm no expert, but a brief read of the following sources suggests it has merit. A simple hookup is limited to 7 devices, but it seems there are ways around that.

The limiting factor with this approach may be the software. Something that might be easy for a programmer can be be nearly impossible for the rest of us.

http://en.wikipedia.org/wiki/Bluetooth
http://electronics.howstuffworks.com/bluetooth2.htm
http://www.bluetooth.com/English/Technology/Pages/Basics.aspx#5

It's remotely (hah!) possible that users could use their own cellphones to communicate to the central PC, with no need for individual remotes.

 

I have been involved with RC airplanes for quite a while and I had thought about it that you can fly several of them at a time. I know that in order to do so you must change the crystal on both the transmitter and receiver. Is this a possibility? Does anyone know about this type of thing?

 

I have been involved with RC airplanes for quite a while and I had thought about it that you can fly several of them at a time. I know that in order to do so you must change the crystal on both the transmitter and receiver. Is this a possibility? Does anyone know about this type of thing?

There are "channels" that are different frequencies changed by a crystal, but using the R/C aircraft frequencies for non-aircraft use is a no-no by the FCC. It is technically possible, but it may be clumsy.

The radios and receivers today are Frequency Hopping Spread Spectrum (FHSS) in the 2.4GHz band, and automatically 'hunt' for unused frequencies to transmit on. These are fairly common modules for hobbyists, but will get expensive, as nearly all are designed for at least 4 communication codes or binary data streams, rather than a single digital channel required for your application.

I mentioned the FHSS above, as it seems exactly what you need, but had no luck finding the Tx and Rx at a reasonable price. This is the same concept Bluetooth runs on.

 

It would be nice. Looks like in the 72 and 75MHZ bands there more than enough of channels. But...Googling I don't find any simple single function transmitter or receiver modules.

Ken

 

Frequency hopping technologies beg the question of what you mean by simultaneous or first. It is entirely conceivable that someone using FHSS could be first by a millisecond, but not recognized. Multiple fixed frequencies avoids that.

To the OP: How close do you consider simultaneous? 1 mS, 10 mS, etc?

John

 

From experience with my jeopardy system, emotionally wired contestants hopped up on caffeine, can be milliseconds apart. At one time I thought about using the transmitters and receivers out of the tiny, $10 ZipZap R/C cars, but the delay time for switch-encode-send-receive-decode-activate is ~100mS. Way too long.

Ken