Manual

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7.3 Proper ultrasonic signal detection
When external noise is high:
- Identify the source. Usual suspects:
- Ultrasonic-based volume or movement detection alarm systems
- Other robots using ultrasonic
- Parktronics
- Sources of very strong white or impulse noise (air guns, air press,
cutters, vacuum cleaner, etc.)
- Rotors of drones/copters
Marvelmind Indoor Navigation System uses proprietary 31kHz frequency for
ultrasonic signal and employs additional filtering to combat external noise.
This also makes the system rather immune against the “usual suspects.”
However, if the external noise is too strong, its source is too close, or it’s
emitting a strong signal on frequencies close to 31kHz or white noise, the
system functionality can be affected.
The best things to do in this case are to (1) identify the beacons that are
affected. Usually, they are those that are the closest to the source of noise;
(2) manually reduce the gain of the affected stationary beacons so that the
signal from the mobile beacon would have a 1000–1800 amplitude. That
would give the best signal-to-noise ratio. Don’t make the gain too high. The
noise will be amplified, but the desired signal will be saturated and signal-to-
noise ratio will be poor.
The gain settings may be very non-linear. There is almost no change at 4000
to 3000. But around 2500, the gain starts reducing very quickly (1200 – for
some HW versions). By setting the gain manually, it is possible to find the
optimal gain to obtain the highest signal to noise ratio so the system can work
even in very challenging external conditions.
When the map is formed, only the mobile beacon is emitting, whereas
stationary beacons are not. Thus, it does not matter how close the mobile
beacon is to the source of the noise.
But it matters how close the stationary beacons are to those sources. So select
the positions of the stationary beacons accordingly - place them further from
the sources of noise