DAC to ADC signal synchronize

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Hello, AVR lovers

I have one problem and can't find decisions. I send encrypted data from DAC and want it to decrypt on ADC, How can I synchronize data and start reading encrypted data from required bit? DAC and ADC is 8bit. Data is sending only in one direction.

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Is "encrypted" really what you mean?

Granted, I'm relatively new to the whole electronics scene, but sending "data" through an analog medium (without a proper modulation) seems like a *really* bad idea to me. I would think it is probably better and easier to use a digital (serial or parallel) protocol to transmit this data. If you need encryption, use a real encryption, not "DAC->ADC".

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I know, but in my situation I can only use analog signal which should be encrypted. So try to encrypt digital signal and send it, after decrytp. Problem is what analog signal is very vulnerable, but now I want to know any algorithm for data sinchronization.

Last Edited: Fri. Sep 7, 2012 - 08:17 PM
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Do you mean "encode" rather than "encrypt". Encode would just mean taking 1..5 and changing this to voltage 1V..5V, transmitting this to an ADC that then turned it back to the numbers 1..5

If you mean encrypt then 1 would be 3V, 2 would be 1V, 3 would be 4V and so on so things were "mixed up".

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clawson wrote:
Do you mean "encode" rather than "encrypt". Encode would just mean taking 1..5 and changing this to voltage 1V..5V, transmitting this to an ADC that then turned it back to the numbers 1..5

If you mean encrypt then 1 would be 3V, 2 would be 1V, 3 would be 4V and so on so things were "mixed up".

I mean what I have digital data -> encription -> DAC -> ADC -> decryption -> digital signal

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You can do that, if you include a form of modulation then demodulation (as random_haker pointed out). It is not going to work otherwise.

I'd skip the whole DAC/ADC thing, or at least only use two values so it's basically just a digital link. Atmost you could use four levels to indicate start/end of a packet.

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Certainly doable.

How many ADC levels are you going to use?

How is the analog signal sent to the ADC, short wire link, long wire, LED, etc?

One method to synchronize them is to reserve an ADC level as a clock. For example, Level 0 is a clock pulse. Send the level 0, then send several data values, then another clock pulse, repeat.

Note that it would be very hard to get 256 levels out of an 8-bit ADC through this system without very careful attention to details. But, if you are going to reserve one level for a clock pulse, then you can split any byte into two 4 bit nibble transmissions. This means you only need 16 DAC/ADC levels, plus the reference clock level.

Bandwidth? Datarate?

Absolute synchronization is possible if you send and synch up on a Start of Packet pattern.

JC

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Thank you all for your helpful advice. I will try to implement.. If succeed I will publish the results and describe solution.