The cabinet I select is also the cabinet used by Mike Douglas for his Altair 8800 Clone computer. He now also offers the cabinet for Altair 8800C builds. This custom designed cabinet by Mike has a look that is very close to the original Optoma cabinet use by MITS and works well for a Altair 8800C design.

While the original Altair 8800 front panel board will now work in this case, Mike is also offering a set of boards that provide, what I feel is a much better solution. Refer to the front panel section below for more details.

The most resent batch of cabinets now have added pre-drilled holes that supports a 9-slot motherboard or two of the Altair 4-slot motherboards. I still needed to drill holes to support my selected power supply solution and card guides though.

A look inside my Altair cabinet reveals my decision to use modern switching power supplies. This is not in alignment with the original heavy linear power supplies that were available back in 1975. Given the Altair clone case being a much lighter constitution than the original Optoma case used by MITS, more efficient and much lighter weight switching power supplies seemed to me a better fit for my 8800C.

There is also the much higher 80% plus efficiency of modern switching power supplies verse the 40-50% of the older linear designs of the day. I guess that makes me Altair 8800C a green system?

I use three switching power supplies to power the Altair. A larger plus 9-volt DC that can supply up to 10-amps. A pair of smaller 16-volt DC at 2-amps each for the plus and minus power. A standard NEMA 5-15P line cord is used to connect to the US 120-volt AC mains power. There is a 1.5-amp, slow blow fuse in line to protect from over current. The main power switch is located on the front of the Altair 8800C. I placed the high voltage wiring in to black plastic Split-Loom for added protection. This cable is routed around the cabinet to the Molex connector that plugs into the isolated section on Mike’s front panel board that supports the AC power switch.

Cooling is provided by the more efficient 120mmx120mmx25mm 5-volt DC fan. Again, a change for the original 120-volt AC fan used in the original Altair 8800. Given the selected fan is 5-volts, a small DC-DC converter is used to convert the power from the 9-volt DC supply down to the 5-volts DC need by the fan. The fan draws about 0.5 amps of current from the 10-amps available on the main 9-volt switcher.

For the motherboard I went with a nine-slot version of the N8VEM’s S-100 backplane version 4 available through Todd Goodman. See www.retrobrewcomputers.org if you wish to obtain one for yourself. This motherboard has the additional advantage of being supported by my selected cabinet.

I am aligning with the original MITS Altir design; I am not using this motherboard's active termination option though. All the S-100 connectors are passively connected. I only populated the nine S-100 connectors, the 6-pin Molex power connector, the three power monitor LEDs and their supporting current limiting resisters.

The two light blue card guides on each end of the motherboard are custom designed and 3D printed off my Prusa i3 MK3. I have made both the right and left card guide files available at the Tinkercad web site. To find the two files, use the show me (search) and enter Altair 8800C.

The two light blue card guides on each end of the motherboard are custom designed and 3D printed off my Prusa i3 MK3. I have made both the right and left card guide files available at the Tinkercad web site. To find the two files, use the show me (search) and enter Altair 8800C.

For the CPU board, I went with a MITS Altair 8800 reproduction CPU board created by Gery Kaufman. This reproduction board used an original 8080 based, MITS REV-1 CPU board as a source. This reproduction follows the original board layout very closely. You even use the original 1975 Altair 8800 CPU assemble manual to build up this board. More information can be found on Gery's web site at the-planet.org.

All the parts used on the board were sourced through a variety of vendors like Digi-Key, Jameco Electronic and some form eBay.

Interfacing all the LEDs and toggle switches found on the front panel of the classic Altair 8800 design is accomplished on my Altair 8800C using a set of boards provided by Mike Douglas. More information is on his DeRamp.com web site.

In the picture above, we see the S-100 interface board used in the two-board set. This design is a great improvement on the original Altair's many wires used to connect the front panel to both the S-100 bus and CPU board.

In Mike's design, there is only a 50-pin ribbon cable that connects the S-100 interface board to the front panel board and an additional 8-pin bridge cable that runs between the CPU board and the font panel interface board. The S-100 interface board is plugged in to the next S100 slots next to the CPU board. This allows the 8-pin bridging cable to connect the two boards together.

From an operational point of view, the new front panel design seems to keep all the original functionality, complete with Altair’s original quirks.

The two-board set is provided as raw boards with only the pre-programmed PIC processor and a few spacers supplied with the boards. The remainder of the parts were easily sourced through Digi-Key and Mouser Electronics.

For floppy drive support, I went with the FDC+ board by Mike Douglas. This neat board allows many options in interfacing a variety of floppy drive types to your Altair 8800 system. The FDC+ is a 100% compatible drop-in replacement for the original Altair FDC solution. There is even support for the use of virtual serial drives where a modern Windows system is set up with a drive server application and through a high-speed serial connection to a special connection to the FDC+ board. With this setup, you can map up to four floppy drive image files to act like physical drives. The following is a table of some drive TYPE options supported by the FDC+:

You also receive three adapter boards that convert the 50-pin connector on the FDC+ board to support the DB-37F connector used on the Altair 8" drives, an IDC-26 adapter for the Altair Minidisk drives and an IDC-34 adapter for standard 5 1/4" floppy drives. None of the adapter boards come with connectors, so you will need to order whatever is needed for your system.

Finally, there is support for up to 64K of static RAM on the FDC+ board. The RAM space is configurable to be placed in most any range needed to back fill any extra RAM needs or to be the only RAM used within the Altair 8800.

Mike ships the FDC+ board fully assembled and tested but remember you will need to buy some parts for the adapter boards. Simply drop the FDC+ board into an open S-100 slot on the Altair 8800 type system, configure it for your needs and you are off and running. For more information visit Mike's site at deramp.com.

For serial input/output, I went with the 88-2SIOJP-R100 board by Marton Eberhard. This board provides hardware to support dual serial ports that are fully compatible with the original MITS 88-2SIO serial interface board. For more information check out deramp.com.

In addition, this board also adds a socket to support one 2716 EPROM or 2816A EEPROM with write capability if an EEPROM is used. Jumper selectable power-on/RESET jump start to an address is also supported. This version of jump start is compatible with memory boards that do not support S-100 phantom signals. Improved power-on clear circuit that eliminates the need to toggle the RESET switch on the Altair 8800.

This board comes fully assembled and test. There are two versions when ordering this board. The R100, like the one I ordered, is populated with two standard 26-pin headers that use two DB-25 ribbon cable assemblies. If you desire the classic Molex connectors found in the original MITS 88-2SIO board, you need to order the M156 option.

Here is my finished Altair 8800C system up and running. While there are still some details, I need to complete in the areas of floppy drive power supplies and other peripherals, the core system is working.