Re: [avr-chat] Audio modem with AVR

[David VanHorn]

FWIW DTMF can be used to send data more quickly than you'd think.

There is a requirement for silence after every digit, which makes it seem slow, but you can drop that silence if the next digit you transmit is different from the current one.   Using "_" for 50mS pause and "." for no pause, a string of same digits is slow, 1_1_1_1_1 but different digits is fast 1.2.3.4.5   Real data would look something like this:  1_1.3.2.5.4_4. 

On Tue, Jul 2, 2013 at 5:58 AM, Pertti Kellomäki <address@hidden> wrote:

Hi Stuart,

Thanks for the pointers.

On Tue, Jul 2, 2013 at 1:37 PM, Stuart Longland (VK4MSL) <address@hidden> wrote:

In your application, you'd basically be looking at the AFSK modulator,
and feeding in your own bit stream from there.  Implementing a full
packet modem with AX.25 would be massive overkill, but the lower level
mechanics are there for what you're after.

Yes, the sending end can indeed be very simple. If there is a transmission error, the phone application can simply ask the user to try again. One twist in my application is that I want to produce actual sound, not feed the signal into a microphone jack, but it won't probably make much difference.

-- 

Pertti

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