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Updates stop when hedgehog is plugged in via USB (SOLVED)

Posted: Sun Jul 29, 2018 10:48 pm
by zlite
I had a weird situation with a hedgehog connected to a RaspberryPi via USB. When it was stand-alone, it updated its position as usual. But when I plugged it into the RPi via USB, it stopped updating. With the help of the Marvelmind tech support, we figured out what was going on. The hedgehog and modem radios cannot be too close together (less than 1m) or it will flood the comms channel.

It turns out that the USB cable acts like an antenna! So when it's plugged in, it increases the gain and overwhelms the radio channel if it's close to the modem.

Solution: Make sure the the hedgehog is further away (at least 2m) from the modem when it's plugged in via USB. Check RSSI value on the mobile beacon in dashboard, it should not be higher than -25 for good communication.

BTW, it's normal for the hedgehog to stop updating for a few seconds when you plug it in via USB, since that resets the board.

Re: Updates stop when hedgehog is plugged in via USB (SOLVED)

Posted: Thu Aug 02, 2018 10:41 am
by admin
zlite wrote:I had a weird situation with a hedgehog connected to a RaspberryPi via USB. When it was stand-alone, it updated its position as usual. But when I plugged it into the RPi via USB, it stopped updating. With the help of the Marvelmind tech support, we figured out what was going on. The hedgehog and modem radios cannot be too close together (less than 1m) or it will flood the comms channel.

It turns out that the USB cable acts like an antenna! So when it's plugged in, it increases the gain and overwhelms the radio channel if it's close to the modem.

Solution: Make sure the the hedgehog is further away (at least 2m) from the modem when it's plugged in via USB. Check RSSI value on the mobile beacon in dashboard, it should not be higher than -25 for good communication.

BTW, it's normal for the hedgehog to stop updating for a few seconds when you plug it in via USB, since that resets the board.

Thank you for highlighting.
Yes, that is right:
- Modem always works with the full radio power (<=10mW or <=10dBm). But that is still strong enough for the beacons to be overloaded by radio signal, if they are closer than 1-2 meters from the modem
- Beacons can be as close to each other, because they don't talk to each other over radio. But they must not be too close to the modem

Yes, USB cable may act as an additional antenna and increase the strength of the signal by a few dB