i know how these "many years" things goes. there are soo many projects I need to complete myself and never have.
I had an RC lawnmower that was all electric, i made from scratch. control circuitry, remote, all of it. took me 2 years until i got it done. finally got it done, had some bugs and other similar issues, but overall it worked ok. it cut the lawn. and i didnt have to physically ride or push it. LOL.
But it burned up in a fire. since the cutting deck was home made out of wood, the drunks decided to burn it in a fire. NICE. :disapprove: (i live in a boarding house environment)
couple of other unfinished projects is a set-top audio spectrum analyzer which i still need to finish, using soviet VFD display tubes.
I also need to finish the MP3 player that uses SD storage, and uses another VFD as its display tube. has a VU meter, and 14 segment alphanumeric. VS1001 decoders are hard to come by, which is why it never got finished.
I made an encrypted cordless phone that worked for awhile and eventually something went screwy in the modem and i never got around to fix it. I used a standard cordless phone with a 24kbit AAC (i think) codec IC, and scrambled the 512-byte stream buffer with a 512bit RSA key in an ATmega128. it worked great. ;-) only major pitfall is the phone ONLY worked if the other person had the same phone, and the audio quality was TERRIBLE, but that was the fastest i could go, as the phone line bandwidth is obviously limited so the modulator couldnt go any faster. it was running fast enough support the 24kbit AAC, I also had to use a 5 block size buffer, not only becuase the encryption took a little while, the audio was choppy. the buffer fixed the choppy audio, but increased the lag time. i didnt care as long as audio wasnt choppy.
the modulator/demodulator consisted of XR2204 AFSK decode/Encode ICs, if memory serves. it was AFSK hot all the time. The "magic" (modulator/scrambler/encoder) sat in between the microphone and the MIC amplifier on the handset. I had to remove the low pass filters to get the entire bandwidth of the handset. Same thing with the earpiece. the demodulator sat in between the earpiece and the amplifier on the handset.
This also meant i couldnt hear plaintext or analog sounds. ONLY the modulated sounds. so i coudlnt hear DTMF tones, or dialtones. just hope like hell it worked. hehe. and it always did. If someone picked up the phone, it would sound like the old time fax machines on the line. lol. I never added a mixer circuit so I could hear the analog as well as digital, and once the Exar IC locked, it would "disable" the analog mix path. it would have been simple to do, just didnt bother. Another cumbersome setback was I had to turn off the MIC modulator while i was dialing, or the "AFSK noise" would interfere and cause issues dialing. But no big deal, after i dialed the phone i would switch the modulator on.
me and a buddy of mine would call each other and use them all the time, and not have to worry about eavesdroppers. Then he passed away, and the project died, never did fix the issue. as he had the other handset.
Before he passed away, the future plans were to fix those issues, and add new ones, such as modulating ASCII text transmissions, so i would know "who" was calling besides what the caller ID said. But i dunno if the PSTN would transmit anything unless the other end "picked up" so it probably wouldnt work until i picked up the phone anyway. I would have also added the ability to change keys on the fly, as I would set my phone up as a master phone, transmit the key to the secondary phone and "rotate keys" for each call or something. Bad thing about that would be, unless i could encrypt the key that i transmit, the encryption could be broken.