Mainly typo fixed

README.md

@@ -41,6 +41,8 @@ The line-out voltage can be as high as 2.7 V<sub>pp</sub> (~1 V<sub>rms</sub>) (
 
 ## Build the library and the 'beacon' demo application
 
+NOTE: In case you want to allow the Pico to control the PTT (*Push-To-Talk*) input of your transmitter, set the appropriate `#define` parameters in `src/aprs_pico_beacon_demo.c`.
+
 ```
 git clone https://github.com/eleccoder/raspi-pico-aprs-tnc.git
 cd raspi-pico-aprs-tnc
@@ -52,24 +54,28 @@ cmake --build build
 
 ## Run the 'beacon' demo application
 
+The analog AFSK audio signal will be available at the filter's line-out. You can probe it by a scope, listen to it by using an audio amp, or connect it to any RF transceiver to send it on the air (ham radio license required).
+
+But for testing the signal integrity, you can feed the signal into the soundcard of your computer and let decode its data content by [Dire Wolf](https://github.com/wb2osz/direwolf) - see down below.
+
 ### Flash the Pico
 
 ```
 cd build
-Flash 'aprs_pico_beacon_demo[.uf2|.elf|.bin|.hex]' to the Pico board as usual.
 ```
 
-The analog AFSK audio signal will be available at the filter's line-out. You can probe it by a scope, listen to it by using an audio amp, or connect it to any RF transceiver to send it on the air (ham radio license required).
+Flash `aprs_pico_beacon_demo[.uf2|.elf|.bin|.hex]` to the Pico board as you're usually doing.
+
 
 ### Test the 'beacon' demo application using *Dire Wolf* (on LINUX)
 
 We can use the famous [Dire Wolf](https://github.com/wb2osz/direwolf) CLI software to decode the APRS data after sampling our APRS audio signal by means of a soundcard.
 
 1. Connect the line-out of our circuit above to the microphone input of your soundcard of your (ALSA-supported) LINUX system.
-2. Check if you can hear the typical APRS 'modem-sound' on your audio output device by monitoring the input signal:
+2. Check if you can hear the typical APRS 'modem-sound' on your audio output device by monitoring the input signal (44.1 kHz, mono, WAVE):
 
 ```
-arecord -f cd -c 1 - | aplay -f cd -c 1
+arecord -f cd -c 1 - | aplay
 ```
 
 3. Install [Dire Wolf](https://github.com/wb2osz/direwolf) on your system. Probably, you just have to run:
@@ -78,7 +84,7 @@ arecord -f cd -c 1 - | aplay -f cd -c 1
 sudo apt install direwolf
 ```
 
-4. Let's sample the APRS audio signal fed to the soundcard and forward the audio stream to *Dire Wolf*:
+4. Let's sample the APRS audio signal fed to the soundcard and forward the audio stream to *Dire Wolf* (44.1 kHz, mono, WAVE):
 
 ```
 arecord -f cd -c 1 - | direwolf -
@@ -90,7 +96,11 @@ arecord -f cd -c 1 - | direwolf -
 
 ### Audio file of the 'beacon' demo
 
-Here is a [recorded audio wav-file](https://github.com/eleccoder/raspi-pico-aprs-tnc/blob/main/doc/aprs_pico_beacon_demo.wav) captured by the soundcard using `arecord -f cd -c 1 -t wav > aprs_pico_beacon_demo.wav`.
+Here is a [recorded audio wav-file](https://github.com/eleccoder/raspi-pico-aprs-tnc/blob/main/doc/aprs_pico_beacon_demo.wav) (44.1 kHz, mono, WAVE) captured by the soundcard using:
+
+```
+arecord -f cd -c 1 > aprs_pico_beacon_demo.wav
+```
 
 You can replay and decode this file by:
 
@@ -98,11 +108,17 @@ You can replay and decode this file by:
 cat aprs_pico_beacon_demo.wav | direwolf -
 ```
 
+## Going on the air: RF-transmission with the *Baofeng UV-5* HT
+
+If you actually want to RF-transmit the APRS signal, you can simply do it by one of the many cheap HTs, like the *Baofeng UV-5*. The complete schematic including PTT control looks like this:
+
+![APRS-Pico with Baofeng_UV-5](https://github.com/eleccoder/raspi-pico-aprs-tnc/blob/main/doc/img/APRS_Pico_with_Baofeng_UV-5R.png)
+
+Don't forget to set the appropriate `#define` parameters in `src/aprs_pico_beacon_demo.c` to configure PTT control.
+
 ## TODO (Dec. 2022)
 
 - [x] Send the APRS message on the console (USB or UART) rather than hard-coding
-- [x] PTT control for RF transceivers
-- [x] Show how to physically connect to a Baofeng HT
 
 ## Ingredients / Acknowledgements
 

include/aprs_pico.h

@@ -42,6 +42,8 @@ audio_buffer_pool_t* aprs_pico_init();
  * \param[in]      latitude_in_deg    The latitude  of the geo-location (in degrees)
  * \param[in]      longitude_in_deg   The longitude of the geo-location (in degrees)
  * \param[in]      altitude_in_m      The altitude  of the geo-location (in meters)
+ * \param[in]      sym_table          The APRS symbol table (e.g. '/' stands for 'Primary')
+ * \param[in]      sym_code           The APRS symbol code  (e.g. '-' stands for 'House QTH')
  * \param[in]      volume             The volume level of the generated signal (0 ... 256)
  *
  * \retval         'true'  - Successful operation
@@ -57,6 +59,8 @@ bool aprs_pico_sendAPRS(audio_buffer_pool_t* audio_buffer_pool,
                         double               latitude_in_deg,
                         double               longitude_in_deg,
                         double               altitude_in_m,
+                        char                 sym_table,
+                        char                 sym_code,
                         uint16_t             volume);
 
 

src/aprs_pico.c

@@ -237,6 +237,8 @@ bool aprs_pico_sendAPRS(audio_buffer_pool_t* audio_buffer_pool,
                         double               latitude_in_deg,
                         double               longitude_in_deg,
                         double               altitude_in_m,
+                        char                 sym_table,
+                        char                 sym_code,
                         uint16_t             volume)
 {
   // NOTE: 'aprs_message' is allowed to be 'NULL'
@@ -261,7 +263,8 @@ bool aprs_pico_sendAPRS(audio_buffer_pool_t* audio_buffer_pool,
                             longitude_in_deg,
                             altitude_in_m,
                             aprs_message,
-                            '/', 'O');
+                            sym_table,
+                            sym_code);
 
   return ret_val == AX25_OK;
 }

src/aprs_pico_beacon_demo.c

@@ -16,37 +16,70 @@
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
 
+
+/* This program demonstrates the usage of the 'libaprs_pico.a' library by showing
+ * how to send a static APRS beacon.
+ *
+ * Optionally, PTT control can be enabled (see the #define section down below).
+ */
+
+// Define whether/how the RPi Pico should control a transmitter's PTT input
+#define PTT_ENABLE                   (false)
+#define PTT_GPXX_PIN                 (1)
+#define PTT_DELAY_BEFORE_TX_IN_MSEC  (400)
+#define PTT_TX_PERIOD_IN_MIN         (10)
+
+
 #include "aprs_pico.h"
 #include "pico/stdlib.h"
 
 #include <stdbool.h>
 
 
+
 int main()
 {
   stdio_init_all();
 
+#if PTT_ENABLE == true
+
+  gpio_init(PTT_GPXX_PIN);
+  gpio_set_dir(PTT_GPXX_PIN, GPIO_OUT);
+
+#endif // PTT_ENABLE
+
   audio_buffer_pool_t* audio_buffer_pool = aprs_pico_init();
 
-  // Let the altitude run over time
-  double alt_in_m = 0.0;
-
-  while (true) // Loop forever
+  // Loop forever
+  while (true)
     {
+#if PTT_ENABLE == true
+
+      gpio_put(PTT_GPXX_PIN, true);
+      sleep_ms(PTT_DELAY_BEFORE_TX_IN_MSEC);
+
+#endif // PTT_ENABLE
+
       // Send an APRS test message
       aprs_pico_sendAPRS(audio_buffer_pool,
-                         "DL3TG",  // Source call sign
-                         "DL3TG",  // Destination call sign
-                         "PATH1",  // APRS path #1
-                         "PATH2",  // APRS path #2
+                         "DL3TG-9",  // Source call sign
+                         "APPIPI",   // Destination call sign
+                         "WIDE1-1",  // APRS path #1
+                         "WIDE2-2",  // APRS path #2
                          "APRS by RPi-Pico - https://github.com/eleccoder/raspi-pico-aprs-tnc", // Text message
-                         10.0,     // Latitude  (in deg)
-                         20.0,     // Longitude (in deg)
-                         alt_in_m, // Altitude  (in m)
-                         128u);    // Volume    (0 ... 256)
+                         48.75588,   // Latitude  (in deg)
+                         9.19011,    // Longitude (in deg)
+                         483,        // Altitude  (in m)
+                         '/',        // APRS symbol table: Primary
+                         '>',        // APRS symbol code:  Car
+                         128u);      // Volume    (0 ... 256)
 
-      // Don't raise too high ...
-      alt_in_m = (alt_in_m < 1000.0) ? alt_in_m + 100.0 : 0.0;
+#if PTT_ENABLE == true
+
+      gpio_put(PTT_GPXX_PIN, false);
+      sleep_ms(PTT_TX_PERIOD_IN_MIN * 60 * 1000);
+
+#endif // PTT_ENABLE
     }
 
   return 0;