See last page for copyright and document info, File: Reeve_GpsNtp-Pi_Setup.doc, Page 5
The system should be powered by a well-regulated, low ripple, electrically quiet power source rated ≥ 1.0 A at
5.0 Vdc (≥ 5 W). Using a poor quality power supply will lead to unreliable operation so be sure it meets these
requirements. One of the most common problems users have with the RPi is inadequate power supply current.
To minimize electrical noise, it is recommended that ferrite beads be installed on the power cable (image
below).
AC wall power adapter rated 12 W at 5 Vdc with North American ac
input plug. One or more clamshell ferrite beads on the dc power lead
may help reduce radio frequency interference from the switch-mode
power supply. This image shows one bead on the right with three
windings of the power lead. The Raspberry Pi uses a micro-USB
connector for power. (Image © 2014 W. Reeve)
Enclosure: If the GpsNtp-Pi is to be used in a sensitive RF environment, the circuit board assembly should be
installed in a metal enclosure. Some considerations are:
When inside an enclosure, the LED indicators on the RPi and GPS circuit boards will be hidden. One way
to handle this is to drill a small hole (~ 2 mm) in the enclosure above the GPS LEDs, so they will be visible
through the hole.
The 5 Vdc power input to the RPi is through a micro-USB connector, which will be inaccessible after the
boards are enclosed. Use a jumper from the RPi board to the rear panel where a power connector is
installed.
A small dc-dc converter may be installed in the enclosure to convert from, say, 12 Vdc input to 5 Vdc for
the RPi. This normally will require an input pi filter for the converter. As above, a jumper will be required
from the RPi board to the converter board. If a converter is used, it will be necessary to check its
specified maximum output filter capacitor size. The RPi board has a 220 μF power input filter capacitor,
so the converter will have to handle at least that much. In addition to the pi filter at the converter input,
MLCC capacitors rated 10 nF should be placed in parallel with the converter input and output.
The RPi circuit board will have to be positioned in the enclosure so the USB and Ethernet connectors are
accessible. A rectangular cutout in the front panel will allow the board to be installed flush with the
panel.
The antenna input on the GPS board will have to be extended to the front panel.
Below are pictures of the GpsNtp-Pi installed in a Box Enclosures B3-160 extruded aluminum enclosure and dc-
dc converter power supply. Enclosure dimensions are 160 long x 108 mm wide x 45 mm high. All holes in the
enclosure were cut using engineering drawings produced specifically for the enclosure. A 5 W dc-dc converter
was installed on a CPS-1 printed circuit board with filter components and PTC resettable fuse and polarity guard
diode. Power input at 12 Vdc is through a 2.1 x 5.5 mm coaxial dc power connector.
