On Wed, Jan 6, 2016 at 8:19 AM, <amulya...@gmail.com> wrote: > I was going through and article about Turning RPi into an FM transmitter . > It consists of just putting a wire on the GPIO4 of Pi which works as an > antenna and run the python script. > > The software uses the hardware of RPi which generates spread spectrum clock > signals to create FM signals.
Right, and the way it works they use the spread spectrum feature to programmatically modulate the frequency of the PWM signal away from 103.3 MHz. Since FM modulation works by changing the base, aka carrier, frequency in proportion to the amplitude of the audio signal you're sending, this happens to behave like a FM modulated signal that is decoded by a FM radio. It's a neat hack---the spread spectrum feature works fast enough to change the frequency of the PWM signal at audio (kHz) rates---it'd be impossible to change it fast enough by twiddling the PWM frequency through its configuration registers. As far as I know, there's no similar spread-spectrum feature on BBB, so this won't work on BBB---although I wonder if something clever could be done on a PRU. > > I dug out more on http://elinux.org/RPi_BCM2835_GPIOs and found out that > GPIO4 's alternate functions include ARM_TDI and GPIO_GCLK. > > I want to know what does the ARM_TDI and GCLK mean. You are looking at IO multiplexing. RPi and Beaglebone both can connect multiple internal peripherals to output pins. The FM feature uses a specific peripheral. It doesn't matter what other peripherals are on alternate functions. > > Now, the main question is, can we make BeagleBone Black as an FM receiver > using only software without using any external FM module ? So now you're talking about FM receiver; neither BBB nor RPi has hardware to receive FM. In theory, with fast enough ADC one could do direct decoding but a) you'd probably need an antenna amplifier and b) the available ADCs are nowhere near fast enough to digitize 100 MHz. You could decode FM signals at carrier frequency 100KHz, probably :) -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
