# Outputting raw bitstream via USB

I am extremely new to this and I'm learning by building stuff myself so please let me know if this is too vague and I'll elaborate if I can. I'm sure this is something very simple, but can't figure out how to do it.

I have built radios before and know how to modulate a signal as ASK but now I'm trying to send a simple bitstream from a USB port to a radio's input. My idea was to use a serial program to dump bytes into the radio input signal but all the research I have done indicates using rs232 or UART or something. I have no experience with this and I don't want some protocol sticking parity bits in all over the place. I simply want to be able to send, for example, 0x1234 as 00000001000000100000001100000100 at a baudrate of $2048$. Can I go further and actually send individual bits like start/stop bits?

My intention is to monitor the frequency with an sdr and then learn how to demodulate the bits from the IQ data.

Is there a simple method outputting bytes directly onto the wire or something I don't know about which will prevent me?

Any help or direction would be greatly appreciated.

• USB doesn't work that way -- there is a lot going on in the differential pair signalling, you can't just bitbang one of the USB wires. Need a whole serial interface engine. Just get an Ftdichip.com FT232, you can easily bitbang the Ft232 pins without needing to dig into the USB specs. Feb 8 '15 at 1:41
• USB raw wire is worse than parity bits, its closer to Manchester encoding with bit stuffing. And its always toggling with bus activity, every 1msec a new frame starts. Feb 8 '15 at 1:43
• You should appreciate that the start, stop and (optional) parity bits in an async serial stream are not there for decoration, they serve a purpose. Feb 8 '15 at 3:09
• Thanks MarkU. That sounds like exactly what I want to do! I already have a pl2302x (usb->ttl) lying around, will that do? and can anyone link me to a good tutorial on this bitbanging stuff? This sounds like my new favourite thing. Feb 8 '15 at 17:23