Successful use of the 555 for encoding eluded me. Too much hash from the square waves. The best solution was an 8038 where wiggling one pin would switch the sine wave output between two frequencies, no transients. I think it was the 567 that I used to detect a mark and space for rtty. First two and then realizing I only had to detect one of the tones. If what you detected was not a mark then it must be a space. About the same time I learned that a CW signal (Ham radio) could be tuned to the 567 PLL and the output fed to the audio. Absolutely no noise on the signal, just the clean tone from the PLL... Those days the soldering iron came on with the light switch in the shop! John Ferrell W8CCW "Extremism in defense of liberty is no vice, and moderation in pursuit of justice is no virtue." -Barry Goldwater "You don't get harmony when everybody sings the same note." -Doug Floyd ----- Original Message ----- From: "William "Chops" Westfield" To: "Microcontroller discussion list - Public." Sent: Friday, August 21, 2009 12:44 AM Subject: Re: [EE]: Historical: LM555 based modem ? > > On Aug 20, 2009, at 6:30 PM, John Coppens wrote: > >>> Does anyone have a link to a schematic of the first modems based >>> apparently on LM555s ? Or anything similar ? Old RTTY modems, >>> including >>> valved ones, are not quite in this class although they come close. >> >> I'm guessing you mean the NE565 (there may be an LM565 version). That >> chip is a PLL which can be used to decode FSK signals. > > Or perhaps the LM567 tone decoder? Having been VERY interested in > making my own modem in the mid to late 1970s, I feel pretty confident > in saying that there was never a modem design based on the 555 timer. > (Note that the 555 was first sold in 1971, so it post-dates the really > early modems.) > > You might find these articles on the 1200Hz/2400Hz "Kansas City > Standard" Tape format to be interesting: > http://www.swtpc.com/mholley/AC30/AC30_Index.htm > http://www.hartetechnologies.com/manuals/SD%20Sales/SD%20Cassette%20Interface%20Manual.pdf > > BillW > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist