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I've built a small consumer device that contains an Arduino Nano. It's coupled to a custom daughter board that allows it to pulse a 12V electromagnet at about 1 hertz as well as inteface to some sensors. It does not intentionally produce any RF emissions like wifi or bluetooth.

I'd like to sell my device in the US, and I'm trying to determine what certification I need to legally sell it. From what I've read about FCC certification, including similar questions here, it's needed by nearly all electronic devices that oscillate above 9 kHz.

So, if I understand this correctly, my custom daughter board wouldn't require FCC certification? The Arduino Nano contains a clock that oscillates at 16 MHz, but I believe it already has FCC certification. Does my composite device constitute something that needs to be re-certified by an FCC approved testing lab? I'm not sure how much I'll be able to sell the device for, and don't expect to make much money, so if I can avoid wasting $10,000 on worthless certification for an unintentional emitter, I'd like to do so.

I'm not sure if this is an appropriate question for this site. If it's not, where could I find an answer to this? I've checked the FCC's website, but aside from vague FAQs, I can't find any way to contact anyone with a clue. I've seen some test labs offering to give me a quote to answer this question, but since they have nothing to gain by telling me "no don't bother paying us thousands to test your device", I'm hesitant to trust a response from them.

Cerin
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    I think this is and apt. question, and I also think it is quite interesting. +1. – Vladimir Cravero Oct 01 '17 at 18:50
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    One way to learn the ropes is to engage the services of a consultation engineer who has taken a product through the certification process before. A few hours of consultation can layout the groundwork ahead of you help you to adjust your product design if needed before you ever show up at a test lab. That alone can save you 1000's in not misstepping on the first trip to a lab. Find someone experienced in the same product category field. – Michael Karas Oct 01 '17 at 21:18
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    Agree with @MichaelKaras. There's a similar device sitting on my desk right now, and I'm happy that a professional consultant checked the design. If the FCC ever knocks on our door, we have the paperwork. – MSalters Oct 02 '17 at 15:06
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  • Ensure solenoid is well clamped on release (reverse diode at least and maybe some RC to slow the edges). 2. Cheap & easy DIY tests that work surprisingly well. Not 100% certain that these will not miss something but usually very useful: Take a portable am band radio and tune across AM broadcast band looking for "spuries". At very low range (a few inches) there WILL be some or even many. At a few feet there may be a few. At ten feet there will hopefully be little. See what range each has and see if you can find how to reduce the largest ones. ...
  • – Russell McMahon Oct 04 '17 at 02:40
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    ... (2) Doing that same with an FM radio works but is less useful.

    (3) The probably now rather rare lowish cost portable manually tuneable, (usually) black & white (typically 12 volt) TVs are excellent for finding signals in the VHF/UHF bands. They do not cover all frequencies but you can SEE signals and also heard them. If you pass the AM radio test well the TV is usually reasonably clean as well.

    The manual tuning is MUCH more useful than station switched TVs which can easily miss signals.

    – Russell McMahon Oct 04 '17 at 02:41