1  # Simple demo of using the SI4743 RDS FM transmitter.
 2  # Author: Tony DiCola
 3  import time
 4  
 5  import board
 6  import busio
 7  
 8  import adafruit_si4713
 9  
10  
11  # Specify the FM frequency to transmit on in kilohertz.  As the datasheet
12  # mentions you can only specify 50khz steps!
13  FREQUENCY_KHZ = 102300  # 102.300mhz
14  
15  
16  # Initialize I2C bus.
17  i2c = busio.I2C(board.SCL, board.SDA)
18  
19  # Initialize SI4713.
20  si4713 = adafruit_si4713.SI4713(i2c)
21  # Alternatively you can specify the I2C address of the device if it changed:
22  #si4713 = adafruit_si4713.SI4713(i2c, address=0x11)
23  # Also if you hooked up the reset line you can specify that too.  Make sure
24  # to pass in a DigitalInOut instance:
25  #import digitalio
26  #reset = digitalio.DigitalInOut(board.D5)
27  #si4713 = adafruit_si4713.SI4713(i2c, reset=reset)
28  
29  # Measure the noise level for the transmit frequency (this assumes automatic
30  # antenna capacitance setting, but see below to adjust to a specific value).
31  noise = si4713.received_noise_level(FREQUENCY_KHZ)
32  # Alternatively measure with a specific frequency and antenna capacitance.
33  # This is not common but you can specify antenna capacitance as a value in pF
34  # from 0.25 to 47.75 (will use 0.25 steps internally).  If you aren't sure
35  # about this value, stick with the default automatic capacitance above!
36  #noise = si4713.received_noise_level(FREQUENCY_KHZ, 0.25)
37  print('Noise at {0:0.3f} mhz: {1} dBuV'.format(FREQUENCY_KHZ/1000.0, noise))
38  
39  # Tune to transmit with 115 dBuV power (max) and automatic antenna tuning
40  # capacitance (default, what you probably want).
41  si4713.tx_frequency_khz = FREQUENCY_KHZ
42  si4713.tx_power = 115
43  
44  # Configure RDS broadcast with program ID 0xADAF (a 16-bit value you specify).
45  # You can also set the broadcast station name (up to 96 bytes long) and
46  # broadcast buffer/song information (up to 106 bytes long).  Setting these is
47  # optional and you can later update them by setting the rds_station and
48  # rds_buffer property respectively.  Be sure to explicitly specify station
49  # and buffer as byte strings so the character encoding is clear.
50  si4713.configure_rds(0xADAF, station=b"AdaRadio", rds_buffer=b"Adafruit g0th Radio!")
51  
52  # Print out some transmitter state:
53  print('Transmitting at {0:0.3f} mhz'.format(si4713.tx_frequency_khz/1000.0))
54  print('Transmitter power: {0} dBuV'.format(si4713.tx_power))
55  print('Transmitter antenna capacitance: {0:0.2} pF'.format(si4713.tx_antenna_capacitance))
56  
57  # Set GPIO1 and GPIO2 to actively driven outputs.
58  si4713.gpio_control(gpio1=True, gpio2=True)
59  
60  # Main loop will print input audio level and state and blink the GPIOs.
61  print('Broadcasting...')
62  while True:
63      # Print input audio level and state.
64      print('Input level: {0} dBfs'.format(si4713.input_level))
65      print('ASQ status: 0x{0:02x}'.format(si4713.audio_signal_status))
66      # 'Blink' GPIO1 and GPIO2 alternatively on and off.
67      si4713.gpio_set(gpio1=True, gpio2=False)  # GPIO1 high, GPIO2 low
68      time.sleep(0.5)
69      si4713.gpio_set(gpio1=False, gpio2=True)  # GPIO1 low, GPIO2 high
70      time.sleep(0.5)