FM transmitter app for initialization and configuration on the badge central expansion port.

apps/fm_transmitter/app.json

@@ -0,0 +1,5 @@
+{
+"menu_item": "FM Transmitter",
+"author": "Pavel Ferencz",
+"main": "rtx.py"
+}

apps/fm_transmitter/rtx.py

@@ -0,0 +1,60 @@
+from arambadge import badge
+from adafruit_si4713 import SI4713
+import displayio
+import terminalio
+from adafruit_display_text import label
+from adafruit_display_shapes.rect import Rect
+import board
+from digitalio import DigitalInOut
+from time import time
+
+class RadioTx:
+    def __init__(self):
+        self.fm = SI4713(badge.i2c, reset = DigitalInOut(board.GPIO2), timeout_s = 0.5)
+        self.fm.reset()
+        self.fm.tx_frequency_khz = 106800
+        self.fm.tx_power = 115
+
+    def process_input(self):
+        buttons = badge.gamepad.get_pressed()
+        if buttons & badge.BTN_LEFT:
+            return True
+        if buttons & badge.BTN_RIGHT:
+            return True
+        if buttons & badge.BTN_UP:
+            return True
+        if buttons & badge.BTN_DOWN:
+            return True
+        if buttons & badge.BTN_ACTION:
+            self.running = False
+            return True
+        return False
+
+    def render(self):
+        screen = displayio.Group()
+
+        screen.append(Rect(0, 0, badge.display.width, 32, fill=0xffffff))
+        banner_image = displayio.OnDiskBitmap(open("/apps/radio/icon.bmp", "rb"))
+        banner = displayio.TileGrid(banner_image, pixel_shader=displayio.ColorConverter(), x=4, y=-2)
+        screen.append(banner)
+
+        app_label = label.Label(terminalio.FONT, text="FM Transmitter", color=0x0)
+        app_label_group = displayio.Group(scale=2, x=40, y=14)
+        app_label_group.append(app_label)
+        screen.append(app_label_group)
+
+        badge.display.show(screen)
+
+    def run(self):
+        display = badge.display
+        self.running = True
+
+        while self.running:
+            self.render()
+            if self.process_input():
+                display.refresh()
+            while display.time_to_refresh > 0:
+                pass
+
+def main():
+    return RadioTx()

apps/radio/radio.py

@@ -13,7 +13,7 @@ class RadioApp:
     def __init__(self):
         self.fm = SI4703(badge.i2c, DigitalInOut(board.D2), channel=103)
         self.fm.reset()
-        self.fm.volume = 7
+        self.fm.volume = 1
 
     def render(self):
         screen = displayio.Group()

requirements.txt

@@ -5,3 +5,4 @@ neopixel==6.0.3
 adafruit_ble==8.0.0
 adafruit_display_text==2.18.3
 adafruit_display_shapes==2.0.8
+adafruit_si4713==1.2.6

tools/find_quietest_fm_freq.py

@@ -0,0 +1,39 @@
+# Run this code through shell in interactive mode in order to find the quietest
+# Frequency available in the area, use an RF-choked USB cable in order to 
+# avoid measuring the noise of the laptop power supply.
+from arambadge import badge
+from si4703 import SI4703
+import board
+from digitalio import DigitalInOut
+from time import sleep
+fm = SI4703(badge.i2c, DigitalInOut(board.D2), channel=106.8)
+fm.reset()
+fm.volume=0
+sleep(0.2)
+freq_to_rssi = {}
+
+# This loop might take about 1.5 minutes to finish
+# The theoretical optimum is 64 seconds, but actually
+# it takes about a minute and a half, because setting 
+# the channel takes time.
+for i in map(lambda x: x/10.0, range(760, 1080, 1)):
+	fm.channel=i
+	# Let the noise stabilize after changing the RX frequency
+	sleep(0.2)
+	freq_to_rssi[i] = fm.read_registers()['STATUSRSSI'] & 0xff
+
+
+
+
+for i in sorted(freq_to_rssi, key=freq_to_rssi.get):
+	print('%5.1f\t%d' % (i, freq_to_rssi[i]))
+
+
+
+
+quietest_freq_1 = min(freq_to_rssi, key=freq_to_rssi.get)
+del freq_to_rssi[quietest_freq_1]
+quietest_freq_2 = min(freq_to_rssi, key=freq_to_rssi.get)
+print("Quietest frequency 1:", quietest_freq_1)
+print("Quietest frequency 2:", quietest_freq_2)
+