I have been working on a bluetooth audio adapter for car, and I plan to put it in a metal enclosure when it is finished.

The bluetooth adapter is very low power and I'm powering it directly from the car's battery. Antenna connector have it's shield/chassis connected to ground, which means unless I use a grommet or something similar, the enclosure would be electrically connected to ground (the enclosure would never be intentionally used as a ground conductor, however). Could this cause any issues?

  • \$\begingroup\$ Any particular reason why it needs to be in metal as opposed to plastic? Metal enclosures can cause more problems than they solve with wireless comms if not carefully designed \$\endgroup\$ – LazyMoggy Aug 8 '19 at 15:13
  • \$\begingroup\$ depends on the antenna connection of the Bluetooth adapter: if it's unbalanced, the outer conductor usually is ground. If it's balanced, you're buildings something that'll swallow most RF energy. Are you sure you want to put a bluetooth audio device in a metal box and then connect an external antenna to its inside? If so, why? \$\endgroup\$ – Marcus Müller Aug 8 '19 at 15:14
  • \$\begingroup\$ @TheAndyEngineer aesthetics, it's important how it will look and feel. For few hundred bucks you don't want to put it in a plastic box.. \$\endgroup\$ – user1258202 Aug 9 '19 at 12:20
  • \$\begingroup\$ @MarcusMüller it's unbalanced. There're lots of wireless devices with metal enclosures - e.g. professional microphone receivers/transmitters and they don't have any problems with that, so why this should be a problem in my case? I don't have any problems with the signal strength either. Btw, I'm asking this question more because of safety stuff. \$\endgroup\$ – user1258202 Aug 9 '19 at 12:24

There are two things to consider here, ESD and wireless signal strength.

For ESD, it can be good to have a metal chassis surrounding the device going to ground to prevent discharges from humans reaching the device. The problem is the antenna's signal strength could be reduced from having a ground plane around it (if the metal chassis is around the whole bluetooth receiver, this would probably block the signal from the receiver).

You could get some software and analyze how the signal strength is affected by grounding vs ungrounding with a 2.4Ghz source in the place of the bluetooth receiver, but it would take the same or less time experimenting with different setups.

Try grounding vs ungrounding. It may be good to try a plastic chassis. SDR's are avalible that can be used as a crude tool for evaluating signal strength if there are not too many other sources around. There are also apps that can do this on a phone

EDIT: If the enclosure works for the signal strength, with the enclosure tied to ground then I would use it to help protect against ESD

  • \$\begingroup\$ I'm asking this more because of the safety reasons. I tried to put the prototype into the actual aluminum enclosure and I have around -40dBm when device is 1 meter away which I assume is a good result and there's nothing I should worry about. \$\endgroup\$ – user1258202 Aug 9 '19 at 12:34
  • \$\begingroup\$ If the enclosure works for the signal strength, with the enclosure tied to ground then I would use it to help protect against ESD \$\endgroup\$ – Voltage Spike Aug 9 '19 at 15:20

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