APO3 technical information


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Bill of Materials:


APO3 Schematic. PDF.

Embedded Software:

The software is written in C and compiled using CCS's PCM compiler. The source code and object code is made available under the GNU GPL license. You are free to distribute and modify the source code as long as you follow the terms of that license.

Software Files:

Case Modifications:

The APO3 case is an off-the-shelf enclosure Polycase. It is the LP-41F. We CNC mill the various cutouts in the APO3 case. The case manufacturer, Polycase, pad prints the label.

Modifications Mechanical Drawing

case modifications drawing

This drawing is alaso available as a larger PNG or PDF file.

Switch Settings:

The voltage threshold and the shutdown delay are configurable with DIP switches. The switch settings are show below and are also printed on the bottom of the circuit board.

Voltage Threshold

Off Off 11.8
Off On 12.1
On Off 12.7
On On 13.05 DEFAULT

Shutdown Delay

Off Off 0
Off On 5
On On 20

OEM T Connectors

We sell a version of the APO3 that comes with pre-installed OEM T connectors. These are the connectors that are found on most VHF / UHF mobile radios. Two 0.25" wide contacts perpendicular to each other. These connectors are available from amateur radio sources such as PowerWerx and hamfests, but there doesn't seem to be information on the Internet as to the original manufacturer part numbers. After multiple hours of research, APRS World has determined the OEM-T connectors to made by TE Connectivity and the following part numbers:

  • 172129-1 for CONN HOUS RCPT 2POS FREE HANGING, MALE CONTACT (OEM-T) (Digi-Key part number A106264-ND)
  • 172130-1 for CONN HOUSING PLUG 2POS NTRL, FEMALE CONTACT (OEM-T) (Digi-Key part number A107344-ND)
  • 42100-1 for CONN RECEPT FAST AWG 14-18 BRASS, FEMALE (FOR OEM-T) (Digi-Key part number 42100-1)
  • 42460-1 for CONN TAB FAST AWG 14-18 BRASS, MALE (FOR OEM-T) (Digi-Key part number 42460-1)

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In order to improve design and supply the best product possible, specifications may change without notice.