Avoiding CE (legitimately) - Page 1
Forum section: electronics / general

author: tom66
author_rank: Super Contributor
timestamp: October 28, 2012, 11:28:15 pm
content: I am being tasked with developing a device which needs to connect to a wifi network. The development budget is fairly constrained.The problem I have is that using a wifi chip on the board itself will mean I need to CE EMC test the whole thing as an intentional radiator. This isn't cheap -- the lowest quote I have got is around £3k.Icoulduse a wifi module, like this:http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en548015However, according to the datasheet, I cannot simply rely on the CE testing of the module (which passes) -- I have to test the system as a whole (so I don't save much going with a chip on the PCB, other than it being easier to pass and easier to design.)I thought about this but then wondered about using a USB wifi dongle? Some of them have easily hackable linux drivers which could be ported to a microcontroller with host USB and DMA. But I think this would come under the same CE restrictions, even though as a home user, you do not need to test your computer in an EMC lab when you plug in the dongle. Would supplying the devices separately be a legitimate way of avoiding intentional radiator testing?Note there is no major budget limitation on the individual items sold, just on the development cost (limiting risk here -- there might only be 20 or so sold, and the product might not even be a success.)Of course I would need to normally CE test the rest but it is cheaper if there is no intentional radiator specification. I can apparently self-certify with a spectrum analyser for the other stuff, but my workplace only paid around £750 for a bare-bones EMC one/two hour test, which is a price I can agree with.No "I am not a lawyer" stuff needed -- I will check the relevant documentation myself, but a pointer would be handy from anyone who has found themselves in the same situation.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 28, 2012, 11:50:10 pm
content: If you're only selling 20 just do what the majority of others do - forget about it.CE marking is enforced by Trading Standards who are far more interested in fake and dangerous goods than anything as obscure and technical as 20-odd units sold into a doubtless highly niche area.Unless you are causing a danger or major nuisance to anyone, nobody will know or care.If you really want to jump through the hoops, maybe a pragmatic solution would be to use an off-the-shelf, packaged RS232 to wifi gateway of some sort. Or maybe adapt one of the various hackable router devices out there, and again use it as a gateway, or add you functionality to the software that runs on it.Or, as you suggested an off-the-shelf USB stick.I believe the only issue with embedded modules is that the approval applies to the combination of radio plus antenna , so for anything that includes the antenna (or whose documentation states that its approval is with a particular antenna), it would be reasonable to argue that this covers the intentional RF side of things.The way you avoid the approvals issue is you sell (or at least list) your device, and offer the wireless interface/gateway as an 'accessory' which you are simply reselling, unmodified, and hence can rely on the original manufacturers' CE declaration.OK technically the system as a whole is theoretically subject to test, however it is clearly accepted that it is impossible to test any significant permutations of products, and hard to argue that a niche product using an of-the-shelf consumer USB stick wifi dongle is any different from any random consumer laptop with the same usb stick.Of course any EMC test house will always tell you that you need a gazillion tests, but they are in the business of selling their services, not telling you that they are not needed, or pragmatic ways of removing your product from the scope of some tests.Also remember that there is no such thing as "CE Testing" or "CE approval".You apply the CE mark to declare that your product complies with the relevant standards (figuring out which are applicable, or making a good argument as to why some do or do not apply can be a major part of the game).It would be entirely reasonable to base a CE declaration on applying standards for a non-radiator for general EMC performance, and citing the modules approvals for the RF performance.

author: Psi
author_rank: Super Contributor
timestamp: October 29, 2012, 12:27:24 am
content: Mike's RS232<-->wifi gateway idea sounds like a pretty good solution. It would also be much easier than coding your own USB comms to talk to a wifi dongle.But i guess it depends how much speed you need. RS232 is limited.You could always use a stock standard wifi router and have ethernet on your device.The only potential issue is reconfiguring the wifi settings, password etc from your box (if needed).It would require a little coding to telnet into the router and update stuff.

author: tom66
author_rank: Super Contributor
timestamp: October 29, 2012, 08:22:44 am
content: Thanks all for the ideas. I will probably self-certify as much as I can. Speed isn't crucial -- they will be downloading a short 1KB file from the server every minute or so. I'll have to investigate the RS232 idea.

author: AndyC_772
author_rank: Super Contributor
timestamp: October 29, 2012, 08:31:15 am
content: £750 should get you the better part of a day's testing, not just a couple of hours - but even so, I'd caution you to remember the (bad) software engineers' maxim: never test for a condition you don't know how to handle.If you assemble a system with approved components, and maintain a technical file on that basis, then you could argue that you had reasonable cause to believe your system to be compliant. That's not actually how the system works, and it's not a solid defence by any means, but you should get away with a slap on the wrist.On the other hand, if you test your system and find it's non-compliant, then you're guilty of knowingly placing non-compliant equipment on the market - and that will land you in trouble.

author: qno
author_rank: Frequent Contributor
timestamp: October 29, 2012, 08:39:07 am
content: I dont think you have to worry too much.I have tested 100 mW babyphones many years ago.The radiated field of the carrier was hardly enough to reach the CE limit at 10 metres.The 3rd harmonic was onlu 3 dB's down but also within the limit.Ever since then i do not worry too much about Radiated emissions.The wifi signal itself would be really small at a distance of 10 m.It would be a poor design if the harmonics of the wifi signal would be bigger.I think the manufacturer is placing this remark in the data sheet to couver its ass.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: October 29, 2012, 01:12:10 pm
content: Quote from: tom66 on October 28, 2012, 11:28:15 pmpage 23 of that datasheet;Quote

author: tom66
author_rank: Super Contributor
timestamp: October 29, 2012, 02:22:23 pm
content: Quote from: Short Circuit on October 29, 2012, 01:12:10 pmRead further ... page 25:Quote