Inboard 386/PC 2mb expansion CLONE

[peterfleeman]

I am getting to this party pretty late, but I just acquired an inboard 386/pc card and I would love to experiment with one of these daughter cards. Any chance we could make more?

 

[sbenting]

I'm also interested in one, if you can make any more.

 

[cb88]

Same here.. still interested and I have two inboards now.

 

[cb88]

@stynx & @harrison.frazier can I get whatever files either of you have I'd like to give this a shot.

Acutally I suspect orienting the ram 90s degrees would work better since each data line would be more equidistanct to the connectors although this may or may not be less convenient to route.

Also since the links got messed up here is a link to the old thread: https://forum.vcfed.org/index.php?threads/seeking-memory-card-for-inboard-386.45638/

 

[harrison.frazier]

@peterfleeman @sbenting @cb88
All, sorry for not seeing these sooner. I put the project on hold when I moved last year and haven't worked on it recently. I have ordered 5 more prototype boards, DM me if you want one.

Here's the BOM for this current revision:

4x dual-simm sockets (will need to snip off plastic pins on bottom to fit proto board) found here:

STRAIGHT SIMM DIMM SOCKET DUAL ROW 60 PIN 30 +30 CONTACTS - LOT OF 2 CONNECTORS | eBay

Find many great new & used options and get the best deals for STRAIGHT SIMM DIMM SOCKET DUAL ROW 60 PIN 30 +30 CONTACTS - LOT OF 2 CONNECTORS at the best online prices at eBay! Free shipping for many products!

www.ebay.com

2x 74F02N Quad 2 Input NOR Gate
2x 74F32N Quad 2 Input OR Gate
8x 512K 70-80ns parity simm modules
You may be able to make it work with larger simms, though no guarantees.

Digi-Key part list - Copy the below to a CSV and import:
Index,Manufacturer Part Number,Manufacturer Name,Description,Attrition %,Requested Quantity 1,Pack Quantity 1,Pack Type 1,Digi-Key Part Number 1,Unit Price 1,Extended Price 1,Minimum Order Quantity 1,Customer Reference
1,BDL-110-G-F,Samtec Inc.,CONN HEADER VERT 20POS 2.54MM,,4,4,Tube,SAM10910-ND,11.59000,$46.36,1,"PL1, PL2"
2,110-44-314-41-001000,Mill-Max Manufacturing Corp.,CONN IC DIP SOCKET 14POS TIN,,4,4,Tube,ED90049-ND,0.75000,$3.00,1,V1-V4
3,C315C104M5U5TA7303,KEMET,CAP CER 0.1UF 50V Z5U RADIAL,,4,4,Cut Tape (CT),399-9859-1-ND,0.23000,$0.92,1,C1-C4
4,UMP1A100MDD,Nichicon,CAP ALUM 10UF 20% 10V RADIAL,,2,2,Bulk,493-15546-ND,0.47000,$0.94,1,"C5, C6"
5,CFR-25JB-52-2R,YAGEO,RES 2 OHM 5% 1/4W AXIAL,,18,18,Bulk,2.0QBK-ND,0.06700,$1.21,1,R1-R18

 

[peterfleeman]

All, sorry for not seeing these sooner. I put the project on hold when I moved last year and haven't worked on it recently. I have ordered 5 more prototype boards, DM me if you want one.

Just seeing this! I definitely would love to build one and contribute however I can. Thank you!

 

[Mike1978]

I can vouch for the 2mb working great I reached out to Harrison of all places over Reddit after seeing his posts on there.

Looking forward to the larger ram models

Thanks Harrison!

 

[chjmartin2]

I can vouch for the 2mb working great I reached out to Harrison of all places over Reddit after seeing his posts on there.

Looking forward to the larger ram models

Thanks Harrison!

View attachment 1252466

I am about to build mine! I have the exact same CPU configuration for my inboard by the way. I do have a 40 MHz crystal by the way and that works with great stability.

 

[Mike1978]

I am about to build mine! I have the exact same CPU configuration for my inboard by the way. I do have a 40 MHz crystal by the way and that works with great stability.

So is there a suggestion to change the oscillator? Not too keen to start desoldering the main card. But I may be tempted. I’ve a few different fpu’s I would like to locate an IIT x2 but not seen one yet.

Anyway onto bigger news with a bit of alteration as advised by Harrison mine seems nice and stable at 4mb! Though there’s 8mb actually sat in the memory slots it maxes out now at 4. I need to perhaps reduce what is in there. Looking forward to the next revision for even more ram access.

You need a steady hand but it’s not too difficult.. (even a ham fisted guy like me managed to solder it)

 

[chjmartin2]

So is there a suggestion to change the oscillator? Not too keen to start desoldering the main card. But I may be tempted. I’ve a few different fpu’s I would like to locate an IIT x2 but not seen one yet.

So it isn't the easiest thing to desolder the oscillator - I ended up breaking mine and I even used a desoldering gun. But you just put in a socket and then you can experiment. The 40 MHz oscillator works great and if you are using a clock doubling chip then it is worth 8 MHz of extra performance.

Anyway onto bigger news with a bit of alteration as advised by Harrison mine seems nice and stable at 4mb! Though there’s 8mb actually sat in the memory slots it maxes out now at 4. I need to perhaps reduce what is in there. Looking forward to the next revision for even more ram access.

You need a steady hand but it’s not too difficult.. (even a ham fisted guy like me managed to solder it)

What is the short connection in the last picture for? Is that required to get the 4 MB card running?

 

[Mike1978]

So it isn't the easiest thing to desolder the oscillator - I ended up breaking mine and I even used a desoldering gun. But you just put in a socket and then you can experiment. The 40 MHz oscillator works great and if you are using a clock doubling chip then it is worth 8 MHz of extra performance.


What is the short connection in the last picture for? Is that required to get the 4 MB card running?

Yes it’s a change in connectivity from pin 19 to pin 15, also severing the trace to 19. This allows the card to address 4mb in place of 2mb

 

[chjmartin2]

Yes it’s a change in connectivity from pin 19 to pin 15, also severing the trace to 19. This allows the card to address 4mb in place of 2mb

I didn’t know that was needed to enabled 4 mb. Is there a GitHub for this that I am missing? My ram gets here today and I am almost done putting together the card although I accidentally soldered the pin headers on the wrong side so that will be fun to reverse.

 

[Mike1978]

I asked Harrison directly the initial design supports 2mb natively. The hack I mentioned opens up 4mb, a redesign will have to follow for anything larger as I understand it..

I’d take the advice given by Harrison to solder those connectors initially with them attached to the inboard card itself as the tolerances aren’t so forgiving for the pcb. Mine went on pretty well and it fits like a glove. (I don’t particular enjoy removing components if soldered wrong, I feel for you - especially as those connectors are not cheap)

I used a couple of floppy disks 1.44mb to act as spacers as they were the perfect thickness.

I was concerned initially about the rear of the daughter card shorting out on the chips below.

It also helps once the connectors are in place to have something you can place the card on connector side down before it’s put in place.

Floppies always to the rescue

 

[harrison.frazier]

I asked Harrison directly the initial design supports 2mb natively. The hack I mentioned opens up 4mb, a redesign will have to follow for anything larger as I understand it..

Yeah I think we'd need to make changes to the actual InBoard if I recall correctly. @stynx knows more about that and made the initial discovery on mapping out all the pins and connections.

 

[chjmartin2]

Almost done. I have to put in the chips but have to look up the right place for the right ones. Anyway, somehow I accidentally bought 8 meg of ram - I thought I was buying 4. Too late to test it tonight. I didn’t do any hack or anything - just built the board. Will it work for 2 meg with the 8 meg chips?

 

[chjmartin2]

M

View attachment 1252755Almost done. I have to put in the chips but have to look up the right place for the right ones. Anyway, somehow I accidentally bought 8 meg of ram - I thought I was buying 4. Too late to test it tonight. I didn’t do any hack or anything - just built the board. Will it work for 2 meg with the 8 meg chips?

Ugh…. Pin headers don’t fit

 

[Mike1978]

View attachment 1252755Almost done. I have to put in the chips but have to look up the right place for the right ones. Anyway, somehow I accidentally bought 8 meg of ram - I thought I was buying 4. Too late to test it tonight. I didn’t do any hack or anything - just built the board. Will it work for 2 meg with the 8 meg chips?

Mine had 8mb in ram as I wasn’t sure if the size of what I had available and ran as 2mb initially and further expanded to 4mb

 

[Mike1978]

M

Ugh…. Pin headers don’t fit

Yeah the tolerances are very low. So it’s why there was advice to solder them in place while connected to the card. can you perhaps remove and resolder?

 

[Mike1978]

Yeah the tolerances are very low. So it’s why there was advice to solder them in place while connected to the card. can you perhaps remove and resolder?

Or are you using standard pin headers?

You need the machined headers as they are a round hole standard pin headers don’t work for this.. the type are listed on the BOM in this forum.

 

[Mike1978]

Or are you using standard pin headers?

You need the machined headers as they are a round hole standard pin headers don’t work for this.. the type are listed on the BOM in this forum.

BDL-110-G-F BDL - Samtec 2.54mm Low Profile Double Row, Screw Machine Terminal Strip - Fast Stock

You need 4 of the above as they are 2 x 10 and you need 2 x 20 for each connector.

In the UK I found these at Toby Electronics but they are far from cheap £60 just for the connectors. So you want to be sure they fit right when you solder them.