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Introducing (and interest check) CircuitTalk: LocalTalk for PowerMac G4

CircuitBored

Well-known member
It is finally time to unveil a project that I have been working on for the last month or so. This is CircuitTalk, a recreation of the StealthSerial and GPort cards that were briefly available for the PowerMac G4 around twenty years ago.

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What does it do?
This card replaces the modem card in PowerMac G4 computers and adds a serial (LocalTalk) port in its place. This enables you to use a PowerMac G4 computer on LocalTalk networks and even act as a LocalTalk -> Ethernet bridge (with one minor caveat, detailed below).

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How was it designed?
I simply identified the components used on the original Gport and StealthSerial cards and used their datasheets to work backwards from there, slowly figuring out how everything was supposed to be connected up. My early proof-of-concepts were... quite a sight to behold.

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Pure chaos here. I was able to get this thing to work but it broke just about every time I so much as breathed on it.

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I soon grew tired of constantly resoldering the horrendously fine-pitched logic board connector so built a much more civilised proto-board version.

The PCB was designed by removing all the components from the original modem card and then putting it in a scanner. From there I used GIMP to pixel-measure the placement of the connector and the standoffs. I then used these measurements to design the PCB footprint in KiCad. I almost got it perfect. The card fits and can be screwed in place but one of the standoffs is ever so slightly misplaced. This will be fixed in the first publicly-available version.

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How fast is it?
In my testing this card runs at around 25KB/s, right up against LocalTalk's theoretical maximum of approximately 28KB/s.

Which machines are compatible?
This card will work in any PowerMac G4 with an AGP slot: late Sawtooths, all Quicksilvers, and all Mirror Drive Door models. At the moment the breakout board only fits into Sawtooth and Quicksilver models but I am working hard on developing a new version that fits into a wider variety of models.

Which machines will be compatible?
The models listed above will all be compatible with the first public version of CircuitTalk.

The main board will fit in an iMac G4 but an entirely different daughterboard will need to be designed to prevent you from having a serial cable dangling out of the back of your computer. The iMac G4 will be the first machine to get CircuitTalk once the PowerMac version is finalised.

The Blue and White PowerMac G3 and the PCI PowerMac G4 use a different internal connector to the later G4s and the positioning is entirely different. There is also a rather large FireWire module in the way. CircuitTalk will need a completely new PCB before it will work! I also need to figure out the pinout of the internal modem connector for these machines as it seems as though it is entirely undocumented.

There is also scope to expand this project to PowerBook G4 and Mac Mini G4 if there is enough demand for it but, as with the G3 version, it will take a large investment of time and money on my part.

Do I need any special software to use this?
Yes. In Mac OS 9 the original GPort extension is required to operate this card and you must patch the LocalTalk Bridge control panel using a tool developed by Griffin in order to be able to do any network bridging. The vanilla version of LocalTalk Bridge will crash your machine if you try to use it. Both these bits of software are archived and will be readily available to all who purchase this gadget. This card also has drivers for Mac OS X.

How much will it cost?
The current target price is £40 (US$54, 48€ at the time of writing) but this may change slightly depending on component availability.

How long until it's ready?
The intial prototype PCBs have been tested and their issues exposed (I placed the mini-din connector upside down, oops!). The main board is 99% ready but the sub-board (nicknamed "Chatterbox") is going to require a significant redesign before I start selling them. At the moment I am expecting to have kits ready to sell by the end of next month, possibly a little earlier if I can find the time.

Do you want one?
This is a question to you, the reader. I am currently nearing the stage where I will be ready to sell these boards and would like to approximate the demand before I order the first batch of finalised PCBs. If you want one of these cards then please leave a comment below expressing your interest.
 

CircuitBored

Well-known member
Interested in the iMac and Mac mini G4 variations!

All in good time. Don't expect these soon™. I don't even own a Mac Mini G4 yet and simply cannot afford one at the moment. The iMac version is something I can almost guarantee within the next six months but the Mini version might not appear for a year or more. It all depends on a lot of variables: luck, time, money, motivation... I'm sure you know what I mean.
 

CircuitBored

Well-known member
would this work in an MDD G4?

Yes, so long as it's running OS 9! The MDD version of the breakout board is 99% finished and the PCB will be ordered shortly. As of tonight the first iterations the non-alpha boards are complete and now I will just spend the next few days doing final inspection of the design (as well as enlisting a second set of eyes to check my work). The main source of delay in getting these shipped now is going to be waiting for various bulk orders of 10-pin IDC cables and obscure connectors to show up...
 

davidg5678

Well-known member
Really cool! One of these plus a SCSI card would make a pretty good bridge machine. I assume this replaces the modem module itself? Any chance it could fit into an iBook Clamshell? It seems like most of the circuit PCB is empty, so maybe further miniaturization would be possible. Are the plans for this open source?
 

Nixontheknight

Well-known member
Yes, so long as it's running OS 9! The MDD version of the breakout board is 99% finished and the PCB will be ordered shortly. As of tonight the first iterations the non-alpha boards are complete and now I will just spend the next few days doing final inspection of the design (as well as enlisting a second set of eyes to check my work). The main source of delay in getting these shipped now is going to be waiting for various bulk orders of 10-pin IDC cables and obscure connectors to show up...
I have OS 9 on my MDD’s hard drive, in addition to tiger, sorbet leopard, and soon Adelie Linux, so it shouldn’t be a problem to use the board (hopefully)
 

CircuitBored

Well-known member
This is something I really really want for my B&W G3 as well.
It's firmly on the to-do list! I already have B&W G3 but need to get my hands on a modem card so I can clone its dimensions. The real challenges are going to be identifying the connector (presumably a 70-pin version of the Molex inter-board conn used in the G4) and assessing its pinout.


Any chance it could fit into an iBook Clamshell?
We'll need yet another variant of CircuitTalk for that! As with the Mini I will also have to get my hands on one first and there will be a lot of research and experimentation needed.

Are the plans for this open source?
No they are not and they won't be any time soon. They most likely will be opened up eventually but I am not willing to put a date on that or promise anything just yet. Sadly I am not yet in a position where I can just give my work away for free. I genuinely wish I were but I simply can't afford it. The profits from CircuitTalk will be being spent on new equipment and currently-unsupported machines that I don't yet own so I can widen the product range. I hope this makes sense.

My current plan is to get to a stage where most of the machines people want these cards in have a version of CircuitTalk available and then start opening up the designs.

I am not doing this to turn a profit; I want everyone who wants one of these cards to have one. That said, I have to have some self respect and charge a fair rate for my labour and the development work that has gone into this project. I have made this first version as cheap as I can justify.
 

volvo242gt

Well-known member
It's firmly on the to-do list! I already have B&W G3 but need to get my hands on a modem card so I can clone its dimensions. The real challenges are going to be identifying the connector (presumably a 70-pin version of the Molex inter-board conn used in the G4) and assessing its pinout.



We'll need yet another variant of CircuitTalk for that! As with the Mini I will also have to get my hands on one first and there will be a lot of research and experimentation needed.


No they are not and they won't be any time soon. They most likely will be opened up eventually but I am not willing to put a date on that or promise anything just yet. Sadly I am not yet in a position where I can just give my work away for free. I genuinely wish I were but I simply can't afford it. The profits from CircuitTalk will be being spent on new equipment and currently-unsupported machines that I don't yet own so I can widen the product range. I hope this makes sense.

My current plan is to get to a stage where most of the machines people want these cards in have a version of CircuitTalk available and then start opening up the designs.

I am not doing this to turn a profit; I want everyone who wants one of these cards to have one. That said, I have to have some self respect and charge a fair rate for my labour and the development work that has gone into this project. I have made this first version as cheap as I can justify.
Re: the modem card, I'll check my B&W in a few seconds....nope, looks like it's MIA. Was able to stick my finger through the hole pretty far.
 

superseth

Member
This is very exciting news. Heard about it over on the CQII BBS and just had to stop by. I remember looking at these for my G4 500 tower back in the 2000's and really wanting one. I had enough beige G3 machines around that it wasn't essential, but I too would love to get one of these and its wonderful to have this option! Great work!
 
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