H220 Integrator Guide
Chapter 2 – Board Overview
Page 17 of 28
The following two pins on the H220 relate to the Speed Radar:
Speed Radar Pulse (pin 25) -
Outputs a square wave with 50% duty cycle. The
frequency of the square wave varies directly with speed. 97 Hz represents a speed of 1
m/s (3.28 ft/s).
Speed Radar Ready Signal (pin 26) -
Indicates when the speed signal on the “Speed
Radar Pulse” pin is valid. In static situations, such as when the vehicle has stopped, the
GNSS position may still have slight variations from one moment to the next. During
these instances, the signal on the ‘Speed Radar Ready Signal’ pin is ‘high’ (or +Vcc),
indicating the speed coming out of the ‘Speed Radar Pulse’ pin is erroneous and not
truly indicative of the GNSS receiver’s actual speed. Therefore, it should not be referred
to or be used. Once the vehicle starts moving again and meets a minimum threshold
speed, the output on the ‘Speed Radar Ready Signal’ pin will go ‘low’ indicating valid
speed information is present on the ‘Speed Radar Pulse’ pin.
Shielding
Typically, the H220 does not require shielding for improving immunity to RF noise incident upon
the board and its various devices. You may, however, wish to shield the H220 from the rest of the
integration if you determine it interferes with other devices or systems.
If you are designing a smart antenna based on the H220 (the H220 and the two GNSS antennas
in close proximity), you will likely want to shield the H220 so that it does not interfere with the
incoming GNSS signals to the antenna.
Note:
Neither pin 25 nor pin 26 has any form of isolation or surge protection. If utilizing the
Speed Radar Pulse output, Hemisphere strongly recommends incorporating some form of
isolation circuitry into the supporting hardware. Contact Hemisphere Technical Support for an
example of an optically isolated circuit.
