A startup was developing a device that would be used directly against the skin.
They did the homework you're supposed to do. They specifically instructed their engineering team to choose a Bluetooth module that was pre-certified and recommended for wearables, so certification would be one less risk on the list.
The module they landed on checked both boxes, and they designed it in.
Then, mid-development, they read the module's actual FCC grant. It restricted use to no closer than 20 centimeters from the human body.
So they had a device built for skin contact, and a module that legally couldn't come near the body.
"Pre-certified" means the module passed testing under the specific conditions written into its grant, and distance from the body is one of those conditions.
Anything used against the skin runs into RF exposure limits the module was never tested for.
So a module can be marketed for wearables while carrying a grant that forbids wearing it. The marketing and the grant are two separate documents, and only one of them is legally binding.
The first advice they got in my Hardware Academy was to take the question straight to their test lab. The lab confirmed the direct route was rough, since closing that 20 centimeter gap meant specialized RF exposure testing and regulatory filings, both slow and expensive.
Then one of the Academy's experts reframed the entire problem. The real question wasn't the 20 centimeter gap, it was how the device should be classified in the first place.
"Wearable" turned out to be a marketing word. To the FCC, anything used against the skin is a portable device, and portable devices have their own exemptions.
At low enough radio power, a portable device can be exempt from RF exposure testing, along with the filings. Their cutoff worked out to 4 milliwatts, and the module put out 2.5.
That's the kind of exemption most people wouldn't know to look for unless they've been through certification before.
He pointed them to the exact FCC guidance document covering those exemption categories, and told them precisely what to review with their test lab.
An apparent dead end turned into a path forward, caught before any certification money was spent.
So there are two lessons here.
First, "pre-certified" might be the most misunderstood word in module datasheets. It only covers the conditions written into the module's grant, so it pays to read the grant instead of the marketing.
Second, your test lab is a design resource. The teams that get through certification cheaply start talking to their lab while they're still designing.
Inside the Hardware Academy, experienced engineers help you catch issues like this while they're still cheap to fix.
Talk soon,
John Teel
Predictable Designs
|
|
|
|
|
|
|
