Can UART or FTDI serial work with communication in only one direction?

Can UART or FTDI serial work with communication in only one direction? or no? Or is there no universal protocol (as in UART only defines the type of connection, not what data is sent though it)  I am building a quadcopter and was thinking of using one of the 2 audio channels to send serial data down one of the spare channels, and the other channel is just connected to a microphone to 'listen' to the noise of the props.

I have 2 major concerns with this method: Will the frequency response and bandwidth of the audio channels be high enough to carry a 115200 bauds signal, or at the very least a 9200 baud signal? and the original question; do I need a 2-way connection for information from the UBLOX GPS or multiwii output? If yes, then i guess the only way to get telemetry is to get one of those 900MHz transmitters, yet another board that I will have to deal with.

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UART's frame the data into standard protocols, usually a start bit, 8 bits of data then either one or two stop bits. So it can only carry digital data. What's the maximum frequency the audio channels can transmit ? Its not going to be high fidelity.

-max- (author)  steveastrouk2 years ago

Ehh, It ain't lookin too good. Knowing composite video has high frequencies components in it, to test the upper limit of the frequency response, I just connected the mobius composite video out directly to the audio and video channel (without the Vsync horizontal and vertical signals, the Rx will not bind to the transmitter and just pick up random static.) and then connected the audio jack to the video in on the TV and it almost sort of wanted to work, but it did not. just some horizontal lines and Genlock issues. So close, but yet soo far. :(

-max- (author)  steveastrouk2 years ago

I answered half of this question so far: the UBLOX GPS output *will* work, as it only spits out data at 5Hz, and the UBLOX software can read that without the need for transmitting data before receiving it. That is good.

Now the issue is purely tring to get the signal cleanly down the audio channel, if it is at all possible. I have connected the Tx pin from the transmitter to the audio input of the transmitter, which goes off to the TV, where the internal headphone jack amplifies the signal (voltage is around 2V peak directly out of the video receiver) and then fed into the FTDI adaptor. It did not work, although the green light on the adaptor is flashing the same as it would when plugged into the GPS. This was only done at 115200 baud, which may be too fast, but I'd have to do a ton of reflashing varius boards and atmels if I want to change that back to 9200.

-max- (author)  steveastrouk2 years ago
And also, some of the connections may actually be I2C instead of UART. Not sure if this makes a big difference when transmitting the digital signals in the analog domain.
-max- (author)  steveastrouk2 years ago
I assume 20,000Hz, I do not have a function generator along with my oscilloscope to test the frequency response. The sound of the data is not nice sounding, but rather strangely, since I have so many discrete boards with FTDI outputs, every one 'sounds' very different. Some have a distinctive 5Hz clicking with lots of high freq. components, while others have less low freq. components and have a softer, mid-toned buzz to them. Thats what I can hear through the TV speakers, and though the piezoelectric module.

I have gave it a quick try and nothing worked, nothing happened. I suppose it did not work because either 115200 baud it too fast, or because the software wants a 2 way connection between the board and FTDI connector, not sure which one it is yet.
iceng2 years ago

UARTs do not need both way. if your uart is not immediately working there are several things to consider 1.inverted_signal, 2.start-bit, 3.stop bits, 4.Parity 5.MSB_position

I did not know that quadcopter had audio channels, why don't you simply use the audio as is, guessing it is an AM format ?

-max- (author)  iceng2 years ago
I have figured out that my 5.8GHz transmitter has 3 separate channels, 2 for audio (left/right I guess) and a composite video. Surely the composite video channel is plenty fast enough, and definitely does not invert, considering that reverse polarity on the composite input will not work at all. I plan on using one channel for the audio of the craft, and the other for telemetry. I guess I will have to measure the output of the FTDI and see how it compares to after passing the signal though the transmitter, see how bad the distortion is.