Since things have slowed down quite a bit with Empeg related tasks, I've turned to developing some related audio bits. One such device is an SPDIF wireless transmitter. It has TOSLINK on both receiver and transmitter and is about 1 inch square including chip antenna. It's only a prototype so far but at least it works. I need to work on improving the range (about 5-10 meters through floors and walls) and make it auto select sample rates, but otherwise it seems to be great.

The nice thing about it is that it does not depend on any particular application like the Airport Express and also is lossless with error correction.

Stu

Dude.

Where's my wireless S/PDIF?

That sounds interesting, please keep us informed of progress!

How is it powered?

Also, when you feel the product is mature enough, the folks here may be interested.

Thanks. Currently it's powered by a wall-wart type supply. See attached picture.

Stu

That is so a better idea than Bluetooth A2DP SBC for wireless headphones. (Or is it too power-hungry for battery applications?)

Peter

The power level is adjustable in firmware and is purported to be better in terms of power usage than Bluetooth with better audio peroformance to boot. I have it set to maximum power for my application though. It uses about 17 mA at this setting for transmitting and 23 mA for receiving. At the lowest setting, this drops to 15 mA for TX with a 20 dB drop in signal.

It would be cool to see something like this in headphones for sure.

Stu

Also the difference in processing an A2DP stream vs. versus the variety of audio streams that SPDIF can encapsulate.

Well, I wouldn't expect it to do forms of SPDIF other than stereo PCM, and stereo PCM is surely easier to deal with than SBC. (Of course even SBC is trivial when compared to the radio modulation, but the chip used presumably internalises all that complexity.) I'm sure 95% of users would be happy with just 44.1KHz/16bit stereo PCM, and adding 48/16 would clean up most of the other 5% (i.e. the DAB/DVB listeners). People who want 96/24 can be accommodated at an alternative price point

Peter

I'm not sure if there is any handshaking on an SPDIF connection — I suspect there's not — or, if there is, how it might work. What would happen if a different stream was sent? If the headphones assumed PCM, it would be noise. If it doesn't assume, then we're back to processing it at least enough to recognize whether it's PCM or not.

All of that may be cheap, but I don't know.

It's not handshaking as such -- the receiver doesn't get to tell the sender what it's capable of -- but the stream is self-describing. Unless either the sender or the receiver is Doing It Wrong, non-PCM streams can't be misinterpreted as PCM.

Peter

If anyone is interested in reading more about this, the chip I'm using is the Nordic nRF24Z1 . It supports up to 24-bit (with compression) or 16-bit uncompressed 48 kHz and S/PDIF or I2S and also wireless SPI and I2C for control.

Currently I am dealing with a frustrating problem of the device not working with anything but 44.1 kHz sampling rates no matter how it's programmed. It may be that it only does 44.1 kHz over S/PDIF and I have to resort to using I2S via S/PDIF receiver and transmitter ICs to get the other supported rates.

Stu

Any chance of an option to power the transmitter via USB?

I can see this as being a good way to play music stored on a laptop for example.

Funny you should ask . The first design was mainly a proof of concept; it works! Yes, the next design which I started yesterday actually will feature USB and TOSlink connectivity on the transmitter end as well as some enhancements to the layout to both ends.

Now I have to decide whether it's worth it to buy a $2000 license for a USB vendor ID!

Stu

Heh, you could always borrow the empeg one. Pretty sure that isn't going to get re-used, so you could use invent a new PID and use the empeg VID

After all, each empeg owner obviously paid a little less than $0.50 toward the VID fund!

Hugo

Cool.. Perhaps I'll do that for my Frankenswitch controllers, too!

I want dibs on DIDs 32->48 !

Something that has particularly annoyed me, we have our own VID but spending $2k on a number is just a tad outrageous, now if somebody at the USB organisation went and looked at the the mechanism that the IEEE use for MAC addresses then it would be a far more pleasant purchasing experience.

You still have to pay the IEEE for an OUI or IAB. It is just cheaper if you're not going to be making many devices as an IAB is 1/3 the price of an OUI.

Yes, I'm aware of that, but you can purchase MAC addresses in much smaller blocks for a much smaller fee, what a brilliant idea.

How many companies who purchase a VID actually use all 65535 PID's available to them? How many just use a handful, say up to 32?

Sub licensing blocks of PID's would be a good thing for everybody.

It isn't quite the same however. If you have an IAB then you're limited to 4096 devices in total. If you have a VID with a tiny PID block you can reuse that as many times as you want.

Sub licensing PIDs would make sense though but there would have to be some incentive not to just buy lots of little blocks if you're a big manufacturer.

FTDI apparently offers that concept to users of their chips: unique DIDs under FTDI's VID.

Sensible.

They do indeed, we have in the past used FTDI chips in products where we've used microcontrollers that do not have USB built in.

Microchip also provide PIDs (for free) for products if you are using a PIC with USB, you just fax over a form and in return you get some PIDs allocated to you.

Just a shame that the people at the top (the USB-IF) want to charge $2k for a huge block that for most people is way over the top. (And it's also delightfully described as an "admin fee")

So is it permissible to sell a product that spits out a default PID from the manufacturer of a USB IC or is it mandated that all commercial USB based products have a unique PID? From what I've read it depends on the marketing of the prpduct and its use of the USB logo.

Stu

No, some of the "big boys" have agreements with the USB-IF that allows them to sub-license their VID to customers, in every single instance I've seen this done it's been for free and there is no charge. However, it always involves requesting your PID's (or block) from the manufacturer, it's a painless process and much less painless than handing over $2K.

You can pay your straight $2K and forego the signing of the agreement that allows you to use the "USB Logo" after your product has passed compliance testing, we went down this avenue, couldn't give a monkey if we can use the fancy USB logo on the product or not, the license agreement runs for 1 or 2 years (can't remember which) after which time you need to pay the "admin" fee again to be able to continue using the USB logo - although your VID is yours forever.

Everybody can apparently sub licence PIDs, I've seen the request page to do so on the USB-IF site, but it's on a specific product by product basis and you have to give quite a lot of detail out about it and I think that you have to be the "developer" of the product for a third party.

If you can get away with using a PIC (shudder, I just got cold sweats) then provided it has a USB interface, you can get a PID for free. I'm sure there are many more microcontroller manufacturers with similar agreements in place, just none of the ones we just so happen to use.

Adrian

Does anybody actually look for the USB logo when buying stuff?

The average user out there will look for the rectangular plug and whether it says USB on the box. They won't care whether it has the official USB logo on it. It isn't like the bad old days of first gen USB hardware with a million and one bugs.

Exactly, who cares about a tiny pretty logo? This is one of the reasons we decided not to trigger the logo license agreement. We just use the letters USB on documentation and stuff, the whole thing is a big con.

(Lets not also forget that the USB protocol was designed by sadists)

I look rather specifically for the "Hi-Speed" logo.

Cheers

Is that the fast one? I get confused

I got completely fished in by that when I got my first digital camera: something about how the spec was worded made me think it was USB2, so I went out and got a USB2 card for my laptop, but of course the camera was only USB1.

Mind you, I've never been totally pleased with USB support on cameras: the one I just got is USB2 at least, but it isn't mass-storage. (I thought, how could I have missed that on the spec sheets at dpreview.com?, but it turns out they don't even list whether cameras are mass-storage or not.) And while I'm not sure whether my first camera was designed before or after mini-USB was invented, the new one definitely doesn't have that excuse for its proprietary connector.

Peter

I've never had a problem with USB support. I leave the USB cable in the box and buy a card reader, like any(I thought) sane person.