Inexperienced and need to find/design 2ch remote control+audio receiver combo

** Desperate Code Scribbling Groper Alert

** Don't tempt me........

** Then go to someone who damn well is.

Explain your loopy app and wanted specs to him.

Have a bank loan ready to pay for the design and development costs.

Off shore manufacture needs to be looked at.

....... Phil

For un-licensed operation, the 418 and 434 MHz freqencies in the U.S. are for remote control purposes only. The signal must be manually actuated and must be intermittent, not contnuous, e.g. garage door opener, tire pressure monitor, keyless entry ... to name a few applications. Encoded voice may be transmitted in the ISM bands, e.g.

915, 2450, 5800 MHz. WCS bands may be used depending upon the aplication.

Aside from that, to achieve several hundred feet (or more) range in a shopping mall using a low-power (

"Frank Raffaeli"

** Like "spread spectrum" or "DECT " cordless phones do.

** Huh ??

A cordless phone could not reliably do that and they use much more than 1 mW.

** See my post for that line of thought. ** But don't expect credible ones from the OP.

He is not the organ grinder, just the code scribbler.

....... Phil

indeed. You're right about DECT. However, other commercial methods are superior. SS phones and DECT have little or no process gain. Also, I'm presuming some infrastructure: repeaters, etc ... and assuming the OP is limited to low power. It's not a trivial task. It also depends upon what the OP means by "voice quality", and the expectations of reliability.

Frank

"Frank Raffaeli" "Phil Allison""

** But have other nice advantages. ** I think that is a bit too much to presume from folk so naive they gave this task to a "programmer". ** Amen to that.

BTW:

Wonder if a GIANT audio induction loop might just do what the OP actually needs.

Need more details to say.

....... Phil

Thank you, Frank, for your helpful post. This all just landed on me the other day, and in addition to the technical matters with which I have little experience, there are the even more daunting legal (FCC) matters with which I am even less familiar. Obviously, no matter how hard I study, there are limits to how much I can learn in a short time, so any pre-processed input from someone who has experience is greatly appreciated.

I *think* I may have found a way to get this project taken on by a professional in this area. It's a tricky business. While Phil has hit upon the "naivety' factor, he missed the "extremely limited resources" part. Here's hoping.

In that case, all I would have to do is create a demo unit for presentation that *does* what we need it to do. It wouldn't have to have the range. It wouldn't have to operate at the frequencies that the end product would. And would not have to have the security. It's the difference between building something that 'works' and designing a 'product'. I feel well up to the former task. The latter scares the hell out of me.

Anyway, I'm still very interested in coming up with the best solution I can, if only to compare it to what actually gets designed assuming that we can get this taken on.

To that end:

1. The target size is about 10x10x3 cm.

1. Battery life needs to be at least a few hours.

2. It needs to have a two channel remote control.

1. The first channel would power up a circuit that flashes a set of LED's marquee style.

2. The second channel would operate a small buzzer motor.

1. Independently, monophonic voice quality audio would be transmitted to the device. It would need to be loud enough to be heard and understood by the wearer.

2. All devices would be performing these actions in unison.

1. The channel 1, channel 2 remotes, and the voice, may occur either alone or in combination with each other.

2. All actions would be under manual control. But the operator would be selecting combinations of actions from a menu in a browser based application and executing them that way. He/she would not be pushing a button on an appliance device like with a garage door opener. The audio would be the output of a sound card in the server. It could be reproducing either decoded mp3 or ogg files, or passing through real time voice from the operator.

1. The transmission would be intermittent, not continuous.

2. It is understood that licensing for use of a higher power transmitter and/or use of the particular frequencies used, may be required.

1. I had been considering the possibility of using repeaters, but am not sure what the legal requirements for that might be.

2. The thing about all of this that scares me the most is the security issue. The fact that I need to operate all devices simultaneously, and that the wearers would actually own the devices, taking them home with them, plus the fact that these people are essentially anonymous, makes it virtually impossible to secure this in such a way that someone could not commandeer control of the devices for their own purposes, if even in a limited area. This is particularly worrisome for the audio. The "normal" methods of securing transmissions between pairs of transmitters and receivers don't apply, here, so far as I can see.

In general, I would be interested in advice as to a general strategy to pursue. There is obviously too much for me to learn in a short time. So my current strategy is to find a direction that looks reasonable, and focus my efforts on familiarizing myself with the specifics of that. And, of course, seeing if I can get this project transfered to people who know what they are doing. ;-)

Thanks again for your help, Steve

Not a problem.

I think this would be your biggest problem. To transmit reasonable voice signal uncompressed would be tough. Using compressed voice would bump up your cost and power budget as well.

Scaling this back, for the moment, and assuming that I am successful at getting a qualified person or team to take on the real work, let me ask about the demo/presentation unit that I would have to build to make that happen.

This would have much less in the way of constraints. No range issues. No security issues.

I am currently planning on using a small off the shelf 418MHz AM 2 channel remote control. And then add a small TDA7000 or TDA7010T based receiver with an LM386 as the amp. Plus a simple marquee flashing circuit for the LED's. The transmitter for the remote controls would be controlled by a USB relay controller from the PC.

Would anyone have any recommendations for off the shelf boards that might combine some of this functionality into a smaller space?

Thanks for any recommendations, Steve

Are you having one remote station, or more than one? We planned on building something like that, and decided that they have to be transceivers. First of all, the master station has to determine what remote stations are in range. At the very least, determine if the remote stations are powered-up, before jamming the airway with data.

Thanks for the details on the application. I may be oversimplifying, but this sounds like a restaurant pager - flashing lights and a small moter, e.g.:

Do you require two-way communication to the (10x10 cm) device, or is it receive only? Security: See "rolling code" algorithms, e.g.:

Other security methods may be superior. The most reliable ones need

2-way communication.

Is the voice arbitrary or can it be a pre-recorded message? This may ease the agency aproval task.

What is the annual volume? Maybe you could interest someone in a speculative R&D project.

Perhaps for your demo you could use one of the jtech units.

Frank Raffaeli

"Steve Bergman"

** That would obviously be because that phrase was NOT in your original post.

BTW: YOU missed this:

" Wonder if a GIANT audio induction loop might just do what the OP actually needs. "

Avoids RF completely and uses only simple audio electronics.

....... Phil

We need one-way communication only.

Yes, I am familiar with the jtech units. They do pretty much everything except the real time audio. The audio needs to be transmitted from the server. I believe the jtechs do have an option to play an internally stored audio message. But, unfortunately, we need a larger repertiore of sound bites, selectable in real time from the base station/server. Still, I should probably go back and reconsider just what I might do with the Jtechs.

Would a rolling code algorithm be compatible with controlling a large number of these acting in unison?

The volume could end up being in the tens of thousands. And yes, we're planning to pitch to a third party who might take this on out of self-interest.

Thanks, Steve

I figured that would be obvious from the fact that they put me on it. ;-)

I didn't miss seeing it. I missed your *meaning*. I thought you were talking about a big loop antenna for the rf.

If I understand you correctly, you are proposing that the loop carry an audio frequency signal and that the receiver devices just amplify the AF directly?

What would be the implications for someone who wanted to cut into the broadcast? They wouldn't have a loop of their own, obviously.

I guess my receiver would just be an AF amplifier with some sort of coil antenna?

I'm guessing that in doing it this way, I'm not really limited on power. The loop could just have the appropriate impedance and be fed by a power amp at whatever power level is necessary.

Thanks, Steve

"Steve Bergman"

** Funny how it says " audio induction loop " isn't it then ?? ** Google " audio induction loop " .

Come back when you are better informed.

....... Phil

communication only.

Thanks for the additional info. If the audio repertoire could be stored in a data-flash, then you may be able to license this device under the remote-control restrictions. MP3 playback chips are cheap if you require compressed storage. There would be several advantages to using the remote-control model that may improve range and reliability, as well as time-to-market.

Yes, rolling codes can be used with many receivers and one master. Each receiver must be addressed separately. I'm assuming the address and command is part of the encoded signal from the master. The tricky part is keeping sychronization.

Frank

Learn from the Boss dumping on you and: DELEGATE!! I.E Just go Buy It - doing this job yourself is a certain loser.

.... Perhaps something based on the guts of those el-cheapo walkie-talkies would work (the ones retailing at USD 40 a pair, a couple of km range and a keypad for "sekrety"). Someone will already have done that.

How come "ressources" is suddently your problem??

If "the man" wants a job done, "the man" can effing well pay whatever it really costs - or - decide that it is not worth doing at all. It is really that easy. Your responsibility is to give some realistic numbers for that deciesion; the easiest way to do that is to ask for some tenders - You *cannot, ever* build a deployable one-off design any cheaper than the stuff you can buy.

Hack a walkie, apply some cardboard, hotmelt glue, spraypaint and whatnot!

In My Experience what people like to see in demo's is "What this product/technology can do for me?" and "WHY do we want this?" NOT the "How is it done?". If one points out that one is cheating, then I.M.E. it is totally accepted as long as one has an idea of the technical issues in order of risk (riskiest goes first).

Your strategy is to stay well away from tasks that you cannot perform with confidence!

All that really counts are the results - if you "cheat", go buy the stuff and it works, what people will remember is: The Result, that the task was handled and done successfully!

The exact same principle applies if you spend 1,5 years hacking some barely working stuff up: people will remember that recall of the crummy product made by that idiot designer (now looking for new challenges) for a long time! Therefore, you cheat!!

First off, I would suggest looking at Zigbee and the various micros out there to support it. It would provide the power levels you need, the long battery life, and the ability to send encoded audio. It would also provide the security that you want. Even simpler would be to use an IR LED broadcast system, with the caveat that you need a lot more base stations...

Charlie

I would look at Nordic Semiconductor. They have low power RF chipsets and data rates fast enough to support spoken audio. Their newest transceiver part, nRF24L01, would be able to address to up to 6 different 'channels'.

-G

Steve Bergman wrote: