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Building an Altair 8800 like it's 1975!


tep392

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I've always wanted to get a real Altair to play around with, but the prices of these S-100 computers has become out of control.  I knew there were several replica's available using emulated hardware with Arduino's and such, but I wanted something more authentic.  When I discovered that all the main boards have been replicated, including a very nicely done full size case, I knew this was the route for me.  I can build this with completely new replica boards or I can mix new and original, as this will be fully compatible with the original hardware.  For the last few years I have dreamt of what it would be like to buy this kit back in the 70's and build my computer at home.  Now I can live out that dream. :)

 

Mike Douglas is the creator of the Altair 8800 Clone .  This isn't a hardware compatible replica but a modern implementation that includes emulation of many of the peripherals and expansion boards.  He designed the case to closely replicate the original, but built a bit lighter since it was intended to house just the clone electronics which were all built into the display board.  The clone is mostly empty space inside. Some time later he designed a front panel board that would replicate the functionality of the original and can be installed in the clone cabinet or even an original 8800.  It's 100% compatible. The design is his own and instead of putting all the electronics on the control panel like Altair did, he added a second board that is installed in the S100 bus as the interface to the panel. This computer was dubbed the 8800C .  You can put a number of different S100 backplanes in it, including copies of the original, which is the route I'm taking.

 

My order from Mike Douglas arrived. Case, front panel boards plus the switches, lights and pre-programmed PIC. I have to commend Mike on the quality of this case.  The fit and finish are top notch.

case_switches_leds.thumb.jpg.46a32327f9b9c4e78effe5b09e644e06.jpg

 

This is my completed panel build.

1st_board.thumb.jpg.1ef9b7d78663acd1010c039dd3b39687.jpg

 

Here are some boards I've been working on the last few nights.  The board on the left is the control for the front panel.  It was designed with a few upgrades like a PIC that has some commonly used loaders, simple games, and a RAM test stored in ROM. It will inject them into the computers RAM by flipping the appropriate switches . The in-process board is a replica of the Rev. 1 MITS CPU board.
Someboards.thumb.jpeg.b72e129025a8e68d45c3cb5c991e30b9.jpeg

 

I'll continue to post my progress here as I build it up and eventually start to expand it.

 

P.S. If you are interested in these S100 computer systems, I suggest you check out Mikes Youtube channel. He has posted a bunch of great video's demonstrating a variety of systems and peripherals, including teletype, paper tape, 8" drives.  He does some interesting hardware and software hacks that are a great insight into what is was like to compute back in the 70's. He even interfaces his computers to a Model 15 teletype circa 1930.

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56 minutes ago, Arnuphis said:

Very nice! I am on the waiting list for an IMSAI clone which is somewhat similar. Please keep us updated!

Cool!  Any links?

 

Update: I ordered a vintage RAM board rather that building up one of the modern boards that are out there.  I feel like I need to keep the system true to it's heritage.  The new boards have lots of RAM, ROM and other bells and whistles that would not have been possible back in the 70's.  I was actually hoping to build a replica of the original MITS 1K board, which came with only 256 bytes populated.  I wanted to go truly old school before upgrading my system. :)  I found a guy that started his own 8800 clone project, and had replicated the 1K board, but he seems to have gone silent and never posted the files for the board.  Anyhow, I ended up ordering a JTM 16K Static RAM board, which is a decent amount for a starter system. 

 

This is the board I just bought.

JTM16K.thumb.jpeg.e0e58860c1dd749d555bb7cce0b58f51.jpeg

A cool thing about many of the memory boards that were made for these systems is their flexible setup options.  This board breaks up the 16k into four 4k blocks, each of which can be located at any 4K boundry in the 64K memory space.  This board also has a banking feature based on Cromemco's that let's you bank the board in and out of the address space.  

 

next step: finish the CPU board and get the S100 backplane parts.

 

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2 hours ago, tep392 said:

Cool!  Any links?

 

Update: I ordered a vintage RAM board rather that building up one of the modern boards that are out there.  I feel like I need to keep the system true to it's heritage.  The new boards have lots of RAM, ROM and other bells and whistles that would not have been possible back in the 70's.  I was actually hoping to build a replica of the original MITS 1K board, which came with only 256 bytes populated.  I wanted to go truly old school before upgrading my system. :)  I found a guy that started his own 8800 clone project, and had replicated the 1K board, but he seems to have gone silent and never posted the files for the board.  Anyhow, I ended up ordering a JTM 16K Static RAM board, which is a decent amount for a starter system. 

 

This is the board I just bought.

JTM16K.thumb.jpeg.e0e58860c1dd749d555bb7cce0b58f51.jpeg

A cool thing about many of the memory boards that were made for these systems is their flexible setup options.  This board breaks up the 16k into four 4k blocks, each of which can be located at any 4K boundry in the 64K memory space.  This board also has a banking feature based on Cromemco's that let's you bank the board in and out of the address space.  

 

next step: finish the CPU board and get the S100 backplane parts.

 

Can you please post the part numbers for the different ICs on that board? The picture is just a touch too small for me to read them clearly.

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19 hours ago, bent_pin said:

Can you please post the part numbers for the different ICs on that board? The picture is just a touch too small for me to read them clearly.

I pulled out the Nikon and took a better pic. There are four RAM chips that were replaced at some point.  Most are original with 1978 date codes.  Hopefully it will work.  One of my first tasks will be to write a small RAM test and key it in the front panel. Everything is socketed which will make repairs a lot easier. :)

DSC_0697.thumb.jpg.62edb45ffd6b7bbb163aba5ecf250afe.jpg

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21 hours ago, Arnuphis said:

I love that you are sourcing original boards. Hopefully that memory board works out of the box. Looks fairly easy to fix if not.

 

Here is the IMSAI link - https://thehighnibble.com/imsai8080/ 

I really like that IMSAI kit.  Those machines have such a great look.  Cool thing about this approach is that you can run a fully decked out machine with all the peripherals for only $280.  A great price in my opinion for what you get. That front panel looks very nicely done.

edit: I was looking at the build videos and noticed it uses an acrylic cover on the back. Nice way to show off the board.

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32 minutes ago, tep392 said:

I pulled out the Nikon and took a better pic. There are four RAM chips that were replaced at some point.  Most are original with 1978 date codes.  Hopefully it will work.  One of my first tasks will be to write a small RAM test and key it in the front panel. :)

DSC_0697.thumb.jpg.62edb45ffd6b7bbb163aba5ecf250afe.jpg

Thank you so much. I appreciate the extra effort. Looks like 2114 4-bit ram used in parallel, some quad flip flops and some xor logic. I'd love to see the schematic for this board.

 

Were you able to source the backplane or did you have to build it?

 

I'm using some 128k x 8 chips for my 6502 pc and some octal latches and bin decoders to activate different pages.

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17 minutes ago, bent_pin said:

Thank you so much. I appreciate the extra effort. Looks like 2114 4-bit ram used in parallel, some quad flip flops and some xor logic. I'd love to see the schematic for this board.

 

Were you able to source the backplane or did you have to build it?

 

I'm using some 128k x 8 chips for my 6502 pc and some octal latches and bin decoders to activate different pages.

This memory board is a copy of the California Computer Systems 2016B.  The manual includes schematics.

California Computer Systems 2016B RAM Manual.pdf

I ordered the 4slot backplane from this guy, along with the connectors.  I'm not looking forward to the 400 solder joints. :( There are STL files for the board guides, but I decided to just buy them from a guy on Ebay because the price was comparable to ordering from a print shop.

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7 minutes ago, tep392 said:

I'm not looking forward to the 400 solder joints.

I would use an iron to set opposing corners on each connector. Then I'd clamp the board so the connectors couldn't move. Then, I'd use solder paste and a fan tipped heat gun to do 20ish joints at a time. You can use a piece of aluminum to block joints that are already finished and gather the heat in the correct rank. Bet you could do the whole thing in a couple hours without going blind. 

 

Do you have an exhaust fan for your bench?

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2 minutes ago, bent_pin said:

I would use an iron to set opposing corners on each connector. Then I'd clamp the board so the connectors couldn't move. Then, I'd use solder paste and a fan tipped heat gun to do 20ish joints at a time. You can use a piece of aluminum to block joints that are already finished and gather the heat in the correct rank. Bet you could do the whole thing in a couple hours without going blind. 

 

Do you have an exhaust fan for your bench?

That's a good idea but I don't have a heat gun or solder paste.  The cost of this build is adding up quick so I'll just use the equipment I have and do them one pin at a time.  Once I get the connector fixed in place it only takes a couple seconds per pin, but it's just tedious. The mounting bolts go thru the connectors, so I'll use them to firmly attach the connecter while I solder.

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1 minute ago, tep392 said:

That's a good idea but I don't have a heat gun or solder paste.  The cost of this build is adding up quick so I'll just use the equipment I have and do them one pin at a time.  Once I get the connector fixed in place it only takes a couple seconds per pin, but it's just tedious. The mounting bolts go thru the connectors, so I'll use them to firmly attach the connecter while I solder.

Be careful not to overheat the connector. Consider jumping from one side to the other for every other joint, instead of going in order.

 

2 minutes ago, tep392 said:

I finished the CPU card.  A lot of components on this one.  9 tri-state buffer chips!  You will notice that the through holes and pads are quite oversized.  Took a lot of solder to do this one.

 

CPUCard.thumb.jpeg.9a0991b2deae30f5ed9cd4614054a5b7.jpeg

That's beautiful, with those wide through-holes it's good that this is a low-speed system.

 

 

This is what's on my bench:

image.thumb.jpeg.ff197bd8bbdd5df2f6160234cb53d09c.jpeg

https://www.amazon.com/gp/product/B07RY5XWVG

 

image.thumb.jpeg.28da4deff7ea682ba47c6153cc6b9180.jpeg

https://www.amazon.com/gp/product/B08SHSSN4X

 

I'm getting ready to buy a heat table to make my SMD work easier.

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If anyone is curious about what it cost to build, this is where I'm at so far.  I still need to buy the power supplies, fan and misc hardware.  I also don't have serial card for connecting to a terminal, so this is a base system other than the extravagant amount of RAM (for 1975). No way to load or store programs yet, so I'll be flipping switches.

Cost1.jpg.3a32e2825712ab81e374f108b885bd84.jpg

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14 minutes ago, bent_pin said:

Be careful not to overheat the connector. Consider jumping from one side to the other for every other joint, instead of going in order.

 

That's beautiful, with those wide through-holes it's good that this is a low-speed system.

 

 

This is what's on my bench:

image.thumb.jpeg.ff197bd8bbdd5df2f6160234cb53d09c.jpeg

https://www.amazon.com/gp/product/B07RY5XWVG

 

image.thumb.jpeg.28da4deff7ea682ba47c6153cc6b9180.jpeg

https://www.amazon.com/gp/product/B08SHSSN4X

 

I'm getting ready to buy a heat table to make my SMD work easier.

Nice setup! I'm using a Weller solder station, which works beautifully for through hole stuff, but that's all it does.

 

edit: forgot to mention that my exhaust fan is home made.  A 12" furnace filter mounted to a cardboard box with a 5" 120V PC fan.  Does a good job of filtering the smoke but takes up bench space.  One of these days I'll move it to the floor and route a hose up to the bench.  

exhaust.thumb.jpg.62b05a353618466c6b51bf8276f65495.jpg

 

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4 hours ago, tep392 said:

If anyone is curious about what it cost to build, this is where I'm at so far.  I still need to buy the power supplies, fan and misc hardware.  I also don't have serial card for connecting to a terminal, so this is a base system other than the extravagant amount of RAM (for 1975). No way to load or store programs yet, so I'll but flipping switches.

Cost1.jpg.3a32e2825712ab81e374f108b885bd84.jpg

Back in May 1975, the computer kit with just the CPU would have set me back $439.  Adding the 4K memory card unassembled would have been another $260, so I'm not doing too bad with this build. :)

Altair_Computer_Ad_May_1975.thumb.jpg.c564943dce8efc97365a73f5a8f541c9.jpg

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15 minutes ago, bent_pin said:

image.thumb.jpeg.04eeddb3f109c7e511f815584e2a7058.jpeg

Very similar to one of the computers from Wargames. Any idea what model that one is?

I've always understood it was an IMSAI 8080. Looks like he had the lid removed.  I wonder if the IMSAI was only a prop or if it was actually being used for some of the footage.  It could have been programmed to provide the scripted responses to the user input.

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18 minutes ago, tep392 said:

I've always understood it was an IMSAI 8080. Looks like he had the lid removed.  I wonder if the IMSAI was only a prop or if it was actually being used for some of the footage.  It could have been programmed to provide the scripted responses to the user input.

Armed with the model of computer, I found this: The WarGames IMSAI – The Official IMSAI Home Page

 

Edit: I found myself rushing through it, but I think I'll slow down and enjoy it over tomorrow morning's coffee 

Coffee Shop Cat GIF

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1 hour ago, bent_pin said:

Armed with the model of computer, I found this: The WarGames IMSAI – The Official IMSAI Home Page

 

Edit: I found myself rushing through it, but I think I'll slow down and enjoy it over tomorrow morning's coffee 

Coffee Shop Cat GIF

Great read!  I got thru most of the IMSAI prop stuff but ran out of time to continue reading.  Interesting that the IMSAI was just doing the flashy lights and the monitor/keyboard was connected to a different computer.  I feel like I read about that fact a while back, but my memory isn't what it used to be.

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