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New "universal" Serial CommSlot printed circuit board design

rabbitholecomputing

Vendor The First
These "universal" serial-only CommSlot PCBs just showed up today, and so far, we've only confirmed that they physically fit in both CommSlot I and CommSlot II sockets, which is a relief. It has footprints for an ESP8266-based Adafruit ESP-12F ($6.95), Raspberry Pi Pico or Pico W stamp, (RP2040-based MCU), or the ubiquitous "Blue Pill" boards (Choose one). This Universal CommSlot serial boards are really simple. All it does is provide voltage translation (to 3.3V, from the 5V CommSlot interface) for the serial pins, a buffer, and a 3.3 volt regulator.

ONLY the serial signals are wired to the edge connector in this revision (2022a). J3 is an SPI pin header which brings out SPI signals from the three different modules to a 3.3V pin header. J4 is the same, but for I²C.

Here's the six-component Bill of Materials, which can cost as low as $5-6 per board. The cost of the ESP8266/Pi Pico/Blue Pill boards is in addition to the base BOM cost. The PCBs cost $2.45 each (shipped), because they're gold ENIG plated, and we didn't order very many. When these are fully tested, we'll eventually be releasing the board design files under an open source license, likely the CERN OHL-S V2 (strongly reciprocal), which is GPL-like, and will order a few hundred PCBs for resale. Until then, if you want one to tinker with, see below.

CL10B104KB8NNWC - 1x 100nF Capacitor, 0603 package, X5R or X7R, >= 10V
CL21A106KPFNNNG - 2x 10uF Capacitor, 0805 package , X5R or X7R, >= 10V
CL10B103KB8NNNC - 2x 10uF Capacitor, 0603 package, X5R or X7R, >= 10V
74LVC3G34DC,125 - 1x ,non-inverting 3-element/triple buffer, VSSOP-8 package
74LVC2T45DC-Q100H - 1x Dual 2-input NAND gate, VSSOP-8 package
NCP1117LPST33T3G - 1x 3.3V Low-Dropout voltage regulator, SOT223-3 package
R1 and R2 are optional 4.7K ohm resistors (1%), to be used as I2C pull-ups, if you're making use of i2c. P/N is RC0603FR-074K7L.

Needless to say, this isn't fully-baked yet, but anybody who wants a PCB and the core BOM components, please let us know. Due to the cost of international shipping, it doesn't make sense to ship these abroad from the US. If anybody here would like to have a handful of blank PCBs sent to their non-American shipping address, please contact us via PM. We're willing to sell these PCBs at near-cost, as this is a hobby board at this point. The initial goal is to be able to use an ESP8266 to connect a Mac to "dial up" to modern Wi-Fi networks, using OpenTransport/PPP, and the ESP8266 or Raspberry Pi Pico W as a bridge to the outside world, albeit at serial speeds.

@David Cook, if you're interested in a PCB, we'll send you one for free. Due to the cost of international shipping, it doesn't make sense to ship these abroad. If anybody here would like to have a handful of blank PCBs sent to their non-American shipping address, please contact us via PM.

Since plenty of you might be wondering "why does this thing exist?", consider this...There are far more CommSlot-equipped Macs with obsolete, useless 28.8/33.6/56K modems still installed than there are CommSlot Ethernet boards in existence. Nobody has made a new CommSlot product in 25 years at this point, presumably. The TAM & Beige G3s were the last Macs that shipped with a CommSlot, in 1997. Plenty of people are making use of Ethernet CommSlot I & CommSlot II boards. If you have one and you're happy with it, this project probably won't be of much interest to you, at least in its current form.

As a reminder, there were a number of Mid-to-late-90s 68K and PPC Macs that were CommSlot equipped:
Please feel free to ask any questions you may have. Answers may not be immediate.
 

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kerobaros

Well-known member
Interested in seeing where this goes, this would make a fun (if slow) wifi card for my Mystic. When development is finished, do you plan on offering the boards for sale with the passives stuffed already, or in kit form?
 

aladds

Well-known member
This is a neat project. I'm in the UK so probably not worth shipping boards out here yet (unless there's others in the UK/Europe who are interested, in which case I would consider distributing!)

Note that you don't actually need a Raspberry Pi to connect to modern WiFi if you use an ESP8266 and a project like this: https://github.com/martin-ger/esp_slip_router

And considering the prices & availability of Pis at the moment, I think this may be the preferred option for now!
 

Corgi

Well-known member
The "initial goal" is for serial speeds, but is there any hope for a future that could go to at least 10Mbit like the Farallon cards did? That would be genuinely useful for bringing my 6500 on to Wi-Fi. Also, I seem to recall that external clocks could drive serial lines towards 1 Mbit, which is still significantly better than 230kbit/s.

Also, any support for the 5 GHz band planned? In this apartment complex, 2.4 doesn't reach outside of the room containing the router, while 5 GHz is usable (about 50 Mbit/s) from my car in the parking lot!
 

cheesestraws

Well-known member
Also, any support for the 5 GHz band planned? In this apartment complex, 2.4 doesn't reach outside of the room containing the router, while 5 GHz is usable (about 50 Mbit/s) from my car in the parking lot!

I'm not sure about the other microcontrollers supported by this card, but Espressif haven't released a chip that'll do 5GHz yet, so a lot of this stuff, which is based on the ESP chips, won't do 5GHz until they do.

This is why AirTalk is also limited to 2.4 GHz. At some point I'd like to do a mashup of this and the AirTalk hardware for comm slot machines, but...
 

rabbitholecomputing

Vendor The First
The "initial goal" is for serial speeds, but is there any hope for a future that could go to at least 10Mbit like the Farallon cards did? That would be genuinely useful for bringing my 6500 on to Wi-Fi. Also, I seem to recall that external clocks could drive serial lines towards 1 Mbit, which is still significantly better than 230kbit/s.

Ten megabits of through is likely not achievable, given the limitations of the serial hardware on the Mac side. I believe the faster serial is good for TWO megabits per second, if externally clocked. This was a "geoport" feature, so these speeds would likely be limited to Macs that shipped with this capability.

Also, any support for the 5 GHz band planned? In this apartment complex, 2.4 doesn't reach outside of the room containing the router, while 5 GHz is usable (about 50 Mbit/s) from my car in the parking lot!
As @cheesestraws has already pointed out, support for 5GHz is a function of the embedded module, not this board. I'm only using the ESP8266 because they're cheap, plentiful, and I had a pile of them already.
 

rabbitholecomputing

Vendor The First
This is a neat project. I'm in the UK so probably not worth shipping boards out here yet (unless there's others in the UK/Europe who are interested, in which case I would consider distributing!)

Note that you don't actually need a Raspberry Pi to connect to modern WiFi if you use an ESP8266 and a project like this: https://github.com/martin-ger/esp_slip_router

And considering the prices & availability of Pis at the moment, I think this may be the preferred option for now!
The RP2040-based Pi Picos are not "Raspberry Pi" SBCs; They're $4 Cortex M0+ based microcontrollers. It's the Raspberry Pi's first microcontroller design. Pico = RP2040, which is a ~$1 microcontroller.
 

aladds

Well-known member
I was more referring to the fact that most people seem to use these to "dial up" to a Raspberry Pi server, although reading back I realise you didn't explicity state that. I just like that with an esp8266 or similar you can connect directly without booting an OS on a "bridge" box.
 

rabbitholecomputing

Vendor The First
Ah ok, understood. Yep, that's the whole point of this endeavour....connectivity to the outside world without the need for external bridges.
 

Aaron707

Member
This is a very interesting idea! I would really like a version for the IIsi and se/30. Internal Wi-Fi modem card would be pretty cool.
 

Trash80toHP_Mini

NIGHT STALKER
Ten megabits of through is likely not achievable, given the limitations of the serial hardware on the Mac side. I believe the faster serial is good for TWO megabits per second, if externally clocked. This was a "geoport" feature, so these speeds would likely be limited to Macs that shipped with this capability.
Don't know if it's been mentioned yet, but there was a mechanism to increase throughput on PowerBooks. Might only have been alleviation of the 'Books inherent serial port limitations? So might not be applicable to your project, but worth a look.

Can't think of the name of the product offhand, a little help anyone?
 

Scott Squires

Well-known member
This is a very interesting idea! I would really like a version for the IIsi and se/30. Internal Wi-Fi modem card would be pretty cool.

If you already have a PDS ethernet card, you might be interested in this:

 
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