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Topic: Audioino? (Read 6 times) previous topic - next topic

Grumpy_Mike

Quote
but im assuming it takes signals from usb and then bit bangs it as a serial connection.

No it has a real UART inside it.


sdinnu

so the usb/fdti chip simply converts usb data signals into TTL signals which are interpreted by the UART, correct? if thats the case could you not just recreate TTL signals through a headphone jack audio signal?

ChrisMicro

#62
Jan 01, 2013, 10:14 pm Last Edit: Jan 01, 2013, 10:22 pm by ChrisMicro Reason: 1
Quote
so the usb/fdti chip simply converts usb data signals into TTL signals which are interpreted by the UART, correct? if thats the case could you not just recreate TTL signals through a headphone jack audio signal?


Audio Signals are AC-coupled, they are not very well suited for NRZ-Codes used by RS232 ( NRZ: http://en.wikipedia.org/wiki/Non-return-to-zero )
This is the reason why I used Manchester Coding ( also use by Ethernet http://en.wikipedia.org/wiki/Manchester_coding ). After some time it turned out that not every PC audio output has the same polarity, therefore I had to switch to differential manchester coding.

The circuit to interface the MC to the PC is in my opinion as minimalistic as possible:



Not all MCs have the same voltage switching level from 0 to 1. They seem to be for the Atmega168 quite similar but may differ to the Atemga328. So the voltage devider should be addapted.

sdinnu

Chris, does your bootloader even use the UART? i thought it could technically run on any pin and all the demodulation was taking place in software?

ChrisMicro

No, it does not use the UART because the UART can't do Manchester Encoding.

Nick Gammon

The audio bootloader can no doubt be made to work (although you would need a way of confirming the process worked, eg. flash an LED) however I can't help you right now because I don't have the hardware to reproduce it.
http://www.gammon.com.au/electronics

sdinnu

so I am running my project off of a rechargeable 3.3v coin cell but the project will be charged using a USB connection. the micro usb has 5 pins so I am considering using power, ground, rx, tx, reset since this will allow for charging and also allow the chip to be reprogrammed. I would like to use an UNO's ftdi chip to program my project but i hear that the UNO is a 5v programmer and it could damage my circuit. How would I allow for 5v ftdi programming? The atmega itself should be fine with 5 volts but my battery and my nrf24l01+ wireless chip probably should not go up to 5volts.

any suggestions?

Nick Gammon

You could make your own programming device (based on the Atmega328P) and run it at 3.3V.
http://www.gammon.com.au/electronics

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