hcooper@esunix.UUCP (Harrison Cooper) (08/21/89)
Thanks to all which answered my question (now relizing it may have been more stupid than I thought) relating to a modem conversion. I suppose if it were possible, manufactures would have done it in the first place. Of course, this also answers why 300 baud units are so much cheaper. I did take the one unit apart and found it using a Exar FSK chip. However, I did find out more than I knew before about modems, so all is not lost due to my request. OK, now if I decide to build a 1200+ modem (why not just buy one? Because I like to build things for the fun of it) who has a good inexpensive chip set (kinda like the one chip phones) that doesn't take much glue to get up and running. Again, I do not really need a smart modem, since I am running only a dumb terminal. H. Cooper N7KST utah-cs!esunix!hcooper
timk@xenitec.uucp (Tim Kuehn) (08/23/89)
In article <1447@esunix.UUCP> hcooper@esunix.UUCP (Harrison Cooper) writes: ...stuff deleted... >However, I did find out more than I knew before about modems, so all is >not lost due to my request. OK, now if I decide to build a 1200+ modem >(why not just buy one? Because I like to build things for the fun of it) >who has a good inexpensive chip set (kinda like the one chip phones) >that doesn't take much glue to get up and running. Again, I do not >really need a smart modem, since I am running only a dumb terminal. > >H. Cooper N7KST >utah-cs!esunix!hcooper I know that intel makes a 2-chip set which will give you a *complete* 2400 baud hayes compatable modem (all you need is an interface to the telco lines, and power supply, and RS232 drivers). Reasonably priced, you could probably build you own modem with these chips for around $100 or so. Don't know the chip designation though. I *have* seen the data sheets though- impressive chip set for what it does! +-----------------------------------------------------------------------------+ |Timothy D. Kuehn timk@xenitec | |TDK Consulting Services !watmath!xenitec!timk | |871 Victoria St. North, Suite 217A | |Kitchener, Ontario, Canada N2B 3S4 (519)-741-3623 | |DOS/Xenix - SW/HW. uC, uP, DBMS. Satisfaction Gauranteed| +-----------------------------------------------------------------------------+
ce1zzes@prism.gatech.EDU (Eric Sheppard) (08/24/89)
In article <1447@esunix.UUCP>, hcooper@esunix.UUCP (Harrison Cooper) writes: > Thanks to all which answered my question (now relizing it may have been > more stupid than I thought) relating to a modem conversion. I suppose > if it were possible, manufactures would have done it in the first place. > Of course, this also answers why 300 baud units are so much cheaper. I > did take the one unit apart and found it using a Exar FSK chip. > > However, I did find out more than I knew before about modems, so all is > not lost due to my request. OK, now if I decide to build a 1200+ modem > (why not just buy one? Because I like to build things for the fun of it) > who has a good inexpensive chip set (kinda like the one chip phones) > that doesn't take much glue to get up and running. Again, I do not > really need a smart modem, since I am running only a dumb terminal. Are you in luck! I just happen to be building a 300/1200 baud FSK modem as a project for Digital Communications. As you saw, the modem uses the Exar 2211 FSK Demodulator chip to convert the tones into data pulses. From my progress thus far, FSK modulation is achieved through a Voltage- Controlled-Oscillator (VCO), which is used to generate two tones (one tone for mark, the other tone for space). To communicate with another modem, your transmitted tones must not interfere with the other modem. To communicate, the two modems merely use different frequency pairs. The originating modem uses the 2205/2225 Hz frequency pair, and the answering modem uses the 1205/1275 Hz frequency pair (as I recall; they may be slightly different). Once I get this thingy up and running (I'm working on the filter circuits now), I would like to try to modify it for PSK modulation, and experiment with 2400 baud systems. Eric Sheppard Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{allegra,amd,hplabs,seismo,ut-ngp}!gatech!prism!ce1zzes ARPA: ce1zzes@prism.gatech.edu -- Eric Sheppard Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{allegra,amd,hplabs,seismo,ut-ngp}!gatech!prism!ce1zzes ARPA: ce1zzes@prism.gatech.edu