Custom Products for the Digital Radio Amateur Enthusiast |
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Product Support Documentation
Model DRA-Pi-Zero
Top side of DRA-Pi-Zero circuit board - shown considerably enlarged.
Bottom side of DRA-Pi-Zero circuit board - shown considerably enlarged.
DRA-Pi-Zero with APRS® connection - shown considerably enlarged.
Schematic Image - Click to download a high quality PDF.
Overview of DRA-Pi-Zero
Things that may not be otherwise obvious:
Parts List:
If you purchased our kit, refer to the parts list and make sure you have all of the components
you need to build it.
Click here
for Parts List.
Construction/Assembly:
Click here for assembly instructions and construction notes - with large photo.
Jumper Settings:
Click here
for Header / Jumper settings and other board connection assignments.
Mini-DIN-6 Pinout:
Click here for MD6 pinout in text.
Click here
for an image of the Mini-DIN-6 data jack.
3.5MM TRRS Pinout:
Click here
for TRRS Pinout.
Installation:
This device is intended to be installed onto a Raspberry Pi Zero 2W (NOT included) - but will
work on any Raspbery Pi with a compatible 2X20 pin header and acceptable power supply. If your
Raspberry Pi has an optional heatsink on the prcessor - it will need to be carefully removed to
provide the necessary clearance for the DRA-Pi-Zero to fully seat on the 2X20 header. A thermal
pad of the proper thickness (not supplied or included) can be installed optionally to allow
the Mini-DIN-6 radio connector to be used as a heatsink with some Raspberry Pi's.
Compatibility:
The DRA-Pi-Zero has not been tested with a Raspberry Pi5, but works fine on a Raspberry Pi Zero,
3 and 4.
Configuration:
Please refer to the instructions on the DigiPi website
for configuration settings using this device.
See Craig's unboxing video.
Refer to the schematic for the pinout of the MD6 and TRRS where all of the logic signals, power
connections, and audio signals are listed.
Custom TRRS radio cables are available from the Digirig Store. They have several pre-made cables that work with the DRA-Pi-Zero for many radios.
Recommended powering requirements:
Raspberry Pi's don't like to be under powered. We recommend a high-current capable power supply for
the system. Something capable of 2 amps or more is best. Separate 3.3V powering is provided for
the digital and analog sections. The board is supplied with 5 VDC from the 40 pin connection from
the Raspberry Pi. Onboard linear regulation is provided for the higher current analog 3.3V
loads (CODEC Analog) insuring low-noise and high signal to noise ratio.
Recommended receive audio input level:
The DRA-Pi-Zero accepts the widest range of audio compared to any other similar radio adapter interface.
The input signal is attenuated by potentiometer R12, giving the broadest range of acceptable levels.
If your receive audio level is adjustable or programmable (at the radio),
we recommend around 2.0 volts P-P. This allows very good signal-to-noise
ratio and low cabling cross talk. This level results in a 50% rotational setting of the
potentiometer. Additional audio level setting is available from AlsaMixer - advanced Raspberry Pi
operational understanding is required.
Transmit audio output capability:
The transmit audio output level is adjusted by the smaller pot (R14). The LEFT / RIGHT "TX" header
selects which channel feeds the transmitter - no soldering is required to make the selection. The
TX audio signal is fed from the high-power headphone outputs to the TX header. Maximim TX output level
is 3.0V P-P with a 500 ohm load and 2.8V P-P with a 30 ohm load - TX pot wide open and AlsaMixer set
to "Max White" (no red). Most portable radios don't need additional AlsaMixer adjustment - but radios
requiring elevated transmit audio (many Yaesu and Kenwood mobiles) may require a master level
setting in the 70's.
PTT Keying:
The DRA-Pi-Zero uses a relay for PTT switching. Some radios don't like a transistor, and using a relay
eliminates any keying issues due to the junction loss of a transistor. FET's and other transistor
switching is fast - but the reed relay we use is almost as fast. For the protocols this hardware
supports - it's plenty fast enough. The 2N7000 is a popular PTT transistor but will lock up in
the presence of RF (RFI). The last thing we want is for the radio interface to lock PTT on solid -
and require a hard reboot to resolve it.
Red "PTT" LED:
The Red LED is in parallel with the coil of the relay. There is no provision to use a separate Raspberry
Pi GPIO to illuminate the Red LED - such as with Direwolf. PTT logic is driven from pin 32 of the
40 pin header.
Online ordering available from the DRA-Pi-Zero main page.
Email Kevin
Custer for support, ordering information, order by check, or support of this
exciting product.
Product of Masters Communications, all rights reserved.
Specifications may change without notice.
Images property of Kevin Custer - W3KKC
Board layout by Kevin Custer - W3KKC.
HTML August 4, 2024, W3KKC All Rights Reserved!