3 ms·

Build it Yourself Modem for under $50 (Byte Magazine, 1980)

11 points by jdblair 5y ago

theamk 5y ago
Interesting! Summary: - They are using acoustic pickup for some reason (possibly for legal reasons?), there are plans on how to construct interfaces from home depot materials. - The modem is fixed speed, 300bps and uses FSK. There is no dialing, pickup/release or ring detection, this is all manual. It is RS232 lines connected to modulator/demodulator and then to phone line. - For modulator, they use NE567 which is designed as a tone decoder, but can be abused to act as tone generator instead. It can be muted by demodulator's "carrier detect", so the modem can auto-shut-off if the other side is gone. - For demodulator they use XR2211, which is apparently special PLL designed specifically for the modems. - Every other page is a full-page ad, plus there are ads inside the text, too. So 50%+ area is advertisement. If you thought that the web invented pervasive advertisements, you are wrong.
- ksaj 5y ago
  An acoustic pickup is a tacit part of the modulate/demodulate pair.
tonyedgecombe 5y ago
I used to buy Byte magazine just for Steve Ciarcia's articles.
- ksaj 5y ago
  Byte Magazine was fun on all levels. It always had technical articles that either involved electronics, or source code, and was DIY in just about every way. Pretty excellent. From this article, I (possibly re-)learned that originating and receiving modems use different frequencies, but I guess that should be obvious from being full duplex. Also I didn't know that most of the handshake is ignored. I'm assuming that means in 300 baud or less, since the handshake also negotiates data speeds. Shocking is the $30/kbyte RAM chips advertised in between, yet the wire stripper/wrapper/unwrapper on page 33 is pretty much the price you would expect it if on sale today.
  - jwalton 5y ago
    Iona Räisänen has a really cool visualization and explanation of all the sounds a modem makes as it handshakes: http://www.windytan.com/2012/11/the-sound-of-dialup-pictured.html?m=1 http://www.windytan.com/2012/11/the-sound-of-dialup-pictured...
mikecoles 5y ago
If you can get your hands on a new-old-stock MX614 IC, it's semi-simple to play with in hardware. There are many software-based packages as well if you're more inclined to enjoy that style. mx614 circuit - https://www.cmlmicro.com/wp-content/uploads/2017/06/FAQs-MX604.pdf https://www.cmlmicro.com/wp-content/uploads/2017/06/FAQs-MX6... attiny style - https://sites.google.com/site/wayneholder/attiny-4-5-9-10-assembly-ide-and-programmer/bell-202-1200-baud-demodulator-in-an-attiny10 https://sites.google.com/site/wayneholder/attiny-4-5-9-10-as... direwolf softmodem - https://github.com/wb2osz/direwolf https://github.com/wb2osz/direwolf

11 points by jdblair 5y ago

Interesting! Summary: - They are using acoustic pickup for some reason (possibly for legal reasons?), there are plans on how to construct interfaces from home depot materials. - The modem is fixed speed, 300bps and uses FSK. There is no dialing, pickup/release or ring detection, this is all manual. It is RS232 lines connected to modulator/demodulator and then to phone line. - For modulator, they use NE567 which is designed as a tone decoder, but can be abused to act as tone generator instead. It can be muted by demodulator's "carrier detect", so the modem can auto-shut-off if the other side is gone. - For demodulator they use XR2211, which is apparently special PLL designed specifically for the modems. - Every other page is a full-page ad, plus there are ads inside the text, too. So 50%+ area is advertisement. If you thought that the web invented pervasive advertisements, you are wrong.

ksaj 5y ago
An acoustic pickup is a tacit part of the modulate/demodulate pair.

tonyedgecombe 5y ago

I used to buy Byte magazine just for Steve Ciarcia's articles.

ksaj 5y ago
Byte Magazine was fun on all levels. It always had technical articles that either involved electronics, or source code, and was DIY in just about every way. Pretty excellent. From this article, I (possibly re-)learned that originating and receiving modems use different frequencies, but I guess that should be obvious from being full duplex. Also I didn't know that most of the handshake is ignored. I'm assuming that means in 300 baud or less, since the handshake also negotiates data speeds. Shocking is the $30/kbyte RAM chips advertised in between, yet the wire stripper/wrapper/unwrapper on page 33 is pretty much the price you would expect it if on sale today.
- jwalton 5y ago
  Iona Räisänen has a really cool visualization and explanation of all the sounds a modem makes as it handshakes: http://www.windytan.com/2012/11/the-sound-of-dialup-pictured.html?m=1 http://www.windytan.com/2012/11/the-sound-of-dialup-pictured...

mikecoles 5y ago

If you can get your hands on a new-old-stock MX614 IC, it's semi-simple to play with in hardware. There are many software-based packages as well if you're more inclined to enjoy that style. mx614 circuit - https://www.cmlmicro.com/wp-content/uploads/2017/06/FAQs-MX604.pdf https://www.cmlmicro.com/wp-content/uploads/2017/06/FAQs-MX6... attiny style - https://sites.google.com/site/wayneholder/attiny-4-5-9-10-assembly-ide-and-programmer/bell-202-1200-baud-demodulator-in-an-attiny10 https://sites.google.com/site/wayneholder/attiny-4-5-9-10-as... direwolf softmodem - https://github.com/wb2osz/direwolf https://github.com/wb2osz/direwolf