[HN Gopher] Replacement PCB Replicates Early 80s Modem
___________________________________________________________________
Replacement PCB Replicates Early 80s Modem
Author : jnord
Score : 99 points
Date : 2024-02-22 12:32 UTC (10 hours ago)
(HTM) web link (tempestfpga.com)
(TXT) w3m dump (tempestfpga.com)
| mytailorisrich wrote:
| Nice Z8 with accompanying EPROM (2764 so 8KiB) on the original
| modem's PCB.
|
| Edit: There's also an S35212, which Google tells me is an "active
| filter for telecommuniations".
| itissid wrote:
| An 8bit microcontroller https://www.cpu-
| world.com/CPUs/Z8/Zilog-Z8681PS.html
|
| The rom is from AMD https://www.ebay.com/itm/303174798174
|
| I can spot a DAC unit from Motorola too
| TedDoesntTalk wrote:
| I have the Hayes 1200 external mint in box, if anyone wants to
| buy it, please email ne.
| reaperducer wrote:
| _I have the Hayes 1200 external mint in box, if anyone wants to
| buy it, please email ne._
|
| Too late. Just last month we had to get one off of eBay in
| order to replace a dead one attached to a computer that, for
| legal reasons, cannot be upgraded.+
|
| + Not being upgradable is one of the reasons it's isolated
| behind a dialup modem and not connected to the company's
| network. Some day I'll have to write a blog post about how a
| group of local politicians can write a law that ends up having
| that effect.
| prmoustache wrote:
| I would say that is a good reason to buy a second one as a
| backup.
| kstrauser wrote:
| I need to hear this story.
| IE6 wrote:
| > Some day I'll have to write a blog post about how a group
| of local politicians can write a law that ends up having that
| effect.
|
| I would love to read about this :)
| dayofthedaleks wrote:
| Take it to your next local HAMfest!
| jeff_vader wrote:
| Related - there's also ESP8266 based TheOldNet wifi modem[1] in
| case you want TCP/IP over wifi networking in your MS-DOS machine
| (or possibly others which have support for SLIP - Serial Line
| Internet Protocol).
|
| [1]: https://github.com/TheOldNet/theoldnet-wifi-firmware-
| binarie...
| myth_drannon wrote:
| You can buy it for 35$ on
| https://www.tindie.com/products/theoldnet/rs232-serial-wifi-...
| msla wrote:
| Is it feasible to build a modem out of a Raspberry Pi Zero or an
| Arduino? You'd need to hook the phone line to the GPIO pins, do
| the ADC and DAC stuff in software, implement the V.22 protocol in
| software, and also implement the Hayes Smartmodem stuff in
| software, meaning this is one of the few times a Hacker News
| reader would have occasion to implement the Hayes Code. Is there
| any show-stopping problem I'm not seeing? Massive electrical
| incompatibility?
| foldr wrote:
| Phone lines operate at way above 5V, so you'd need some level
| shifting at least.
| mtve wrote:
| 9V battery was enough for two modems to communicate back-to-
| back, without dial tone or ringing signals, just "ATD"
| command on one and "ATA" on another.
| missjellyfish wrote:
| Telephone Line Voltage is anywhere between 48 to 90V DC,
| depending on where in the world you are and which standards
| apply.
| mikewarot wrote:
| You _need_ a "hybrid network" to connect to the telephone
| system. You'll also need a relay to take it off hook, etc.
|
| There can also be hundreds of volts on the line at various
| times, not to mention induced voltages during storms.
|
| Once you've handled that, it should be fairly easy to generate
| the right signals and do handshaking. An RP2040 / raspberry pi
| pico should be more than adequate.
| bluGill wrote:
| You need a bit more hardware (see other posts), but most modems
| from the late 1990s until laptops stopped coming with a modem
| worked this way - using the CPU which was probably slower than
| a pi to do the work. Such models basically never worked in
| linux (I'm not sure why), they didn't have the best reputation
| as far as quality but they worked.
| sumtechguy wrote:
| > I'm not sure why
|
| If I remember correctly as most of them were DSPs and need a
| driver to load a binary blob to work correctly. All of them
| had their own spin on the process. Most linux distros did not
| ship the blobs either. So you would have a bit of fun
| cracking it out of some random windows EXE just so you could
| put it somewhere the driver could reach it. It was worth the
| extra 20-50 bucks it would cost just to _not_ buy one of
| those things and use it in linnx. Remember this was at a time
| when a bit of ram (1MB) would cost 100+ dollars. There was a
| reason they were cheap. They did not have enough hardware to
| run standalone and relied on the OS to do the loader work.
| _Microft wrote:
| This was called a "softmodem":
| https://en.wikipedia.org/wiki/Softmodem
| retrac wrote:
| You'll need some analog circuitry. Not much, but phone service
| has some kinks electrically speaking.
|
| A phone on-the-hook appears like an open circuit to direct
| current. Off-the-hook the circuit is closed, and current starts
| flowing. (Pulse dialing and "flash" signals open/close the
| circuit, telegraph style.) And ringing on POTS is done by
| applying about 20 Hz AC to the line at around 100 volts --
| enough to make an electric motor ring a bell, or unpleasantly
| surprise someone playing with the "low voltage" phone line.
|
| So you need to block the AC ringing (and other spikes), block
| the DC bias voltage (while presenting a phone-like impedance to
| the line), and then join both the DAC and ADC to the same two-
| wire line with matched impedance. It could be anywhere from a
| couple transformers and a few resistors and caps, to a very
| complicated arrangement with amplifiers, active noise
| cancelling and gain control circuits, etc. (There used to be
| dedicated ICs for those things.)
|
| POTS, by its analog nature, is extremely flexible in practice.
| A couple 9V batteries are often enough to make two old phones
| work as intercoms. But the faster you want to go the more
| important it will be to match the expectations of a POTS line
| exactly.
| nickt wrote:
| There's also some upgrades available for the Hayes Stack
| Chronograph.
|
| https://biosrhythm.com/?p=1546
| nsxwolf wrote:
| Can I take a moment to express my appreciation for products
| encased in aluminum extrusions? Why aren't more products like
| that today?
| bongodongobob wrote:
| It requires custom machining rather than injecting plastic into
| whatever kind of molds you have.
| nsxwolf wrote:
| But it seems simpler in some ways than injection molding. You
| make a single die that's a 2D cross section, extrude as much
| aluminum as you want, cut it into pieces.
| 0_____0 wrote:
| I think it's just the reverse of this. It's easier than
| ever to get custom injection molding done, even at
| relatively low scales. Yes, the setup cost for machining
| holes in extrusion is very low, but if you're going to make
| even 1,000 of something you might consider getting a low
| volume tool made.
| formerly_proven wrote:
| Extruded aluminium cases are fairly popular for smaller
| production runs because they're generally off-the-shelf
| with only the faceplates being custom (usually laser cut
| and engraved). So the fixed costs are basically zero but
| the unit costs are somewhat high (aluminium is expensive).
| Lots of stuff is just made in large enough runs that molded
| parts become cheaper overall (very nonzero fixed costs but
| very low unit costs).
| bluGill wrote:
| If you only need one than the cheapest is find a local
| machinest and say "make a case to fit" It will be all
| manual and designed on the mill/lathe except where
| experience says "better draw this part up first" (one in a
| while they will scrap a part because it doesn't fit, but
| overall still cheap). If you need 5-100 then draw it up in
| CAD and have a machinist (need not be local) throw it on
| their CNC machines. If you need 1000 or more then design an
| injection process. Where I put exact numbers that is
| because the overhead vs efficiency of the process makes
| this best, where I didn't put anything it is a judgement
| call, it isn't clear when exactly ones process should be
| abandoned for the next. (even then sometimes I'm wrong, but
| for discussion I'm close enough - if you are doing real
| world work consult a real manufacturing engineer)
|
| Injection molding is great for making a lot of parts, but
| the cost of designing a working mold means the upfront
| costs are a lot higher and if you cannot reuse that mold
| enough to spread that cost across many parts it isn't worth
| doing.
| zokier wrote:
| Not sure what you mean, extrusions are by definition produced
| by extruding, not machining. The die needs to be machined
| somehow, but so do injection molds too; neither is more or
| less custom?
| myself248 wrote:
| I wish I could get a good face-on view (scan?) with dimensions,
| of that old extrusion. It'd be fun to 3d-print a clone; of
| course it won't look the same but it would get some stuff in
| the right approximate shape.
|
| Guess I should probably buy one, cad it up, and sell it again.
| marssaxman wrote:
| If it's just that classic style you are looking for, and not
| the exact Hayes design, you might find interesting options
| from Protocase, Metcase, Bud, or one of the others:
|
| https://www.protocase.com/products/electronic-
| enclosures/alu...
|
| https://www.metcaseusa.com/en/Enclosures/Aluminum-
| Enclosures...
|
| https://www.budind.com/series/general-use-boxes/ext-
| series-e...
| bluGill wrote:
| FCC rules around radio emissions used to be tougher, so
| aluminum was popular in early home computers. I'm not sure
| exactly when the rules changed, but seems like sometime in the
| last 1970s or early 1980s. then it took time for manufactures
| to realize plastic was enough cheaper as to be worth learning
| how to do.
| dylan604 wrote:
| At the time CPUs hit the 1GHz speeds, there were all sorts of
| discussions on the shielding so we don't start radiating
| ourselves. The internet is a fun place, facts be damned!
| devwastaken wrote:
| Aluminum extrusion requires that the PCB fit into the slots.
| Large PCBs are expensive to prototype and most of the space
| isn't necessary anymore.
|
| Also the enclosures are quite costly in comparison to plastic,
| and most aluminum enclosures don't provide any meaningful
| benefit other than EMI shielding (when grounded).
|
| They don't even act as a heatsink unless you go outside the
| generally expected methods. However at that point it's usually
| easier to throw on a heatsink and have ventilation holes.
|
| But yes I do love aluminum extruded chassis.
| bsder wrote:
| Everything has wireless and metal interferes with it.
| rasz wrote:
| We quickly learned how to do proper emf testing and design out
| leakage. From 1979 Atari 800 ~3kg of alloy extrusion we got to
| 1982 Commodore 64 with thin metal plate followed by ~1986
| models using aluminum sticker rf shield, and that was all with
| only the most rudimentary engineering work. Nowadays you find
| source of radiation leakage and filter it out right there on
| the pcb before it becomes a problem.
| ChuckMcM wrote:
| It is a nice aesthetic right? The short answer is that in
| volume, injection molding is cheaper. That said, you can buy a
| wide variety of "standard" extrusion products if you want to
| build a custom case for something. This happens fairly
| regularly in custom instrumentation. Most recent example I saw
| as a tranceiver that used 80/20 quarter round extrusion (#1517)
| on the corners and sheet aluminum for the sides top/bottom. The
| front was likely laser cut or milled aluminum. I don't think
| it's been opened up yet for service so I don't know if there
| were any additional structural supports inside.
| jdyyc wrote:
| Oooo... The functionality isn't unique but the implementation is
| awesome. I love the big red leds and hardware power switch etc...
| Very clean.
|
| Now I want one that fits in a USR Courier case.
| bfrog wrote:
| Ah yes, built to last 40+ years in a _metal_ enclosure. Love it.
| mrlonglong wrote:
| Now I want one for my obsolete USR Robotics V92 modem (upgraded
| from 33.6k)
| jamesfmilne wrote:
| It's featured in an episode of Adrian's Digital Basement if you
| want to see someone build one and try it out.
|
| https://youtu.be/De5ufcDueRU?si=cY7kKrlY8slFIM3G
|
| I did something similar with a Raspberry Pi inside as US Robotics
| Sportster 14400 Modem, running pppd over serial to give an old
| Mac internet access. I also rigged it to play the modem handshake
| when starting the PPP session.
| gwbas1c wrote:
| _What do you use this for?_ This should be front and center on a
| page like this.
|
| I _suspect_ the wifi modem telnets. Does it ssh? I suspect the
| target use case is connecting to a telnet BBS from vintage
| hardware.
___________________________________________________________________
(page generated 2024-02-22 23:01 UTC)