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Go wireless!

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Now that I know how to transmit FM short distances (e.g. across the house), is anybody interested in a wireless FM output design for the Retrocade?

What features would people want? I guess stereo would be nice...

How would you like to set the frequency?

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Now that I know how to transmit FM short distances (e.g. across the house), is anybody interested in a wireless FM output design for the Retrocade?

What features would people want? I guess stereo would be nice...

How would you like to set the frequency?

Can we use the internal FPGA PLL to output frequency to the exterior, and then have some sine wave (do we need sine wave?) generator lock to this frequency ? That would allow for very interesting designs....

http://www.xilinx.com/support/documentation/application_notes/xapp879.pdf

What you think ?

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Now that is a freaking cool idea! I think the frequency should be set as a control change coming from the MIDI device that is controlling the RetroCade. Theoretically the best way to handle an FM transmitter module would be to implement it as a wishbone core, like the ym2149. Then it could be plugged into the ZPUino and the RetroCade sketch could be setup with code that would take a control change from the RetroCade Dashboard or a MIDI keyboard and forward it to a register in the FM transmitter code to set the frequency.

Nice!

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Can we use the internal FPGA PLL to output frequency to the exterior, and then have some sine wave (do we need sine wave?) generator lock to this frequency ? That would allow for very interesting designs....

http://www.xilinx.co...tes/xapp879.pdf

What you think ?

Nah, too complex :-).

My project uses a DCM to generate a high frequency (320MHz), that runs a 32 bit accumulator.

Every clock cycle it adds (desired freq)/320,000,000 * 2^32 to the accumulator.

The upper bit then flips on and off at the desired frequency (however with around 3ns of jitter) - just plug in a wire and you are done.

For 91.0Mhz at either side of the FM band gives constants of 1222387958 and 1220374692, with a center frequency constant of 1221381325.

My simple demo makes a square wave, but you if you were to use 1221381325 +/- 1,000,000 (e.g, a 16 bit signed sample plus five zeros) you can transmit high quality audio. Switch between channels at 19.2KHz and you should get stereo too.

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