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--- radios:gm300 [2023/07/16 14:29] – ei9iub
+++ radios:gm300 [2023/07/16 14:44] (current) – ei9iub
@@ Line 8: / Line 8: @@
 The radios are usually programmed through the front RJ45 connector, using a so-called RIB (Radio Interface Box).
 Most cables purchased online are known as RIB-less, and are essentially USB - TTL devices such as the FT232x with a diode inline between TX / RX.
+It also possible to program these radios directly using the Raspberry Pi GPIO Serial pins, as the levels output are acceptable to the radio.
+Be sure to map the serial port correctly,
 See below for a Homebrew Motorola RIBless cable schematic:
@@ Line 23: / Line 27: @@
           +---+
+The rear 16 pin accessory connector:
+                     RADIO TOP
+         +---+---+---+---+---+---+---+---+
+         | 2 | 4 | 6 | 8 | 10| 12| 14| 16|
+         +---+---+---+---+---+---+---+---+
+         | 1 | 3 | 5 | 7 | 9 | 11| 13| 15|
+         +---+---+---+---+---+---+---+---+
+                    RADIO BOTTOM
+                  AS SEEN FROM BACK
+EXT SPKR             9 EMERGENCY ALARM
+MIC AUDIO IN        10 IGNITION CONTROL
+  --> 3 PTT                 11 RX AUDIO OUT    <---
+EXTERNAL ALARM      12 PROG I/O 12
+  --> 5 FLAT TX AUDIO       13 SW A+ SENSE
+PROG I/P 6          14 PROG I/O 14
+  --> 7 GROUND              15 INT SPKR +
+COS (PROG)          16 EXT SPKR +
+Audio interfacing the Raspberry Pi and GM3X series radios.
+These radios can also have PTT driven directly by the Pi without a transistor, but __this is not advised__.
+                                               +------+
+                           +-------------------|PI GND|
+                           |                   +------+
+                           | NPN
+                           +-<|      440Ω     +----------+
+                              |-----/\/\/\----|PI GPIO 17|
+                           +-/|               +----------+
+                           |
+   +-----------------+     |
+   |GM3X0 PTT (PIN 3)|-----+
+   +-----------------+
+   +---------------------------+    22µF    +------------+
+   |GM3X0 RX AUDIO (PIN 11)    |---+||------|   USB MIC  |
+   +---------------------------+            +------------+
+   +---------------------------+    22µF    +------------+
+   |GM3X0 FLAT TX AUDIO (PIN 5)|----+||-----|   USB SPK  |
+   +---------------------------+            +------------+
+   +-----------------+                      +------------+
+   |GM3X0 GND (PIN 7)|----------------------|PI AUDIO GND|
+   +-----------------+                      +------------+