Hi everybody,

Finally i found a forum that talks only about electronics .. !!
Anyway .. first i am kind of new to the electronics world .. i have a good background, but not expert
alright, i'm thinking of a project to do with one of my friends in the university in our free time .. i'm thinking to do a "Voice Encryptor" .. but the main idea is to make it totally using hardware (with no PC required) ..
so we thought of a basic idea to use it as the base of our project .. the concept is too simple for the first step in our project then we will try to make it more advance if this works ..
anyway, the idea is to take the voice signal (which is analog) and insert it to a ADC (ADC0804) which will gives us digital output of 8-bit using the continues conversion circuit shown in this image ..



then do some process to the digital output (this process will be considered as the encryption)

then enter the result 8-bits to an DAC to re-convert it to analog (i'm using DAC0800LCN)



so that if we entered a normal sin wave from a function generator and graph the output on a Oscilloscope the output will not be a proper sin wave .. so we can consider that as a kind of encryption then the result analog signal we will take it and re do the whole process to it but with changing the digital process that we apply it to it so that the new process will decrypt the signal and the output analog signal will be the same sin wave we entered in the first time ..

this is the main idea i'm working for .. but right now i was trying to understand how to properly conect the ADC to DAC together ..
so i'm trying to connect the output from the ADC directly to the input of the DAC with no any process applied to it to just see how it works .. but i'm facing some problems knowing what should i connect some pins to !!
like the (Vref/2) in the ADC or the and the (Vref+ & Vref-) and the (VLC) in DAC ??

i tried to use an 5V PK-PK sinusoidal as an input for the ADC and i connected the (Vref/2) in the ADC to a +2.5V and in the DAC i connected (Vref+) to a +5V and (Vref-) to a -5V and the (VLC) to a GND and i haven't connected the (COPM) to anything .. the result was sinusoidal too, but the problem was that it was 10mV PK-PK only !!!

so any idea how to help me in my project .. and sorry for the very long post


Regards,
Ata

I suggest you dump the antique components, use a modern microcontroller, a PIC with in-built A2D and hardware PWM DAC (or use an R2R ladder DAC) can easily digitise the audio, encrypt it in software, and output an analogue signal.

Just be aware that simple bit scrambling will yield an analog signal with a bandwidth that is potentially much higher than your original signal, so if you have a bandwidth-limited channel, such as a phone line, that the encrypted signal has to traverse, you will lose information and not be able to descramble on the receiving end. If you do have such a channel, you have to choose an encryption method that will not exceed its bandwidth.

Originally Posted by OmarAta

well the problem that i don't know how to program the PIC .. and in this time these are just the components i have with me ..
but is there is any wrong with the way I'm using (except being too ancient ) ??

How were you planning doing the encryption?, and were you planning running 9 core cable between the transmitter and receiver?.

A PIC gives a single chip solution, by just learning a little programming.

and you said encrypt it using a software .. do you mean a PC ??

No, inside the PIC.