The smell of solder and progress... and some glue

I've began working on the second board of the computer. Since most of this second board requires the first board I've gone ahead and super glued the two boards together.

Layout

I'm going to describe how my layout is going to work. If you've read my previous entries you'll notice I'm using two breadboard style perfboards. For me this makes wiring easier but there are problems with using them:
1. You need two because one that would be long enough for all the ICs would be ridiculous.
2. It's easier to keep all ICs using the data bus and address bus on the same board. Luckily the only thing that uses the address bus is the ram.
3. There isn't an effective way to put the hex displays on the board directly.

For issue two I put the 1802, the ram, and IC 8 and 9 on the same board. Now any of you who know the schematics well are thinking, "What about IC 4 and 5?" well.... I ran out of room. My first idea was to have them on a separate board with just the hex displays that could be mounted directly to a case but that doesn't work because they are also used in the control logic. So I'm going to have to channel the data bus over to the other board anyway.

I'm making the case out of wood in which I'll mount both boards with long sides touching. The switches and hex displays will be mounted directly to the case.

K-Elf

Found another neat article about the Cosmac Elf. This one talks about using an eeprom on an Elf.

Muller Lab Schematic

I like this schematic better compared to the original. For me it is easier to follow.
Muller Lab Cosmac Elf

It breaks down the original schematic into sections (Basic, Control, Memory, Input, Output, etc)

Adding some features

As those who have read my blog have noticed while I'm not using the typical Cosmac Elf layout I am using a standard circuit. Well I'm thinking of adding some things to the circuit. More specifically adding a series of LEDs (Cause the hex displays are expensive) to show the current address. I need to look into if I need latch or if I can just attach it to the address bus.

Progress after a hiatus.

Sorry for the lack of progress. I got distracted with some of my many hobbies and since I was working on the tedious part of the computer I lost interest. Today I started on the databus and have the first four bits wired to the latch chip. I still have to get the last four bits and then wire all 8 bits to the processor.

Well I've got the address lines done for the ram chips. That was the most time consuming and tedious part of construction. This is board one of possibly three. This is the CPU, Ram, power, and the support chips for the data switches. The second board will contain the control logic for the cpu and the remaining switches. A possible third board will contain the actual switches and output. This may just be embedded into a case I'm not sure yet.

This is a picture of the underside of the board. As you can see (not my sloppy soldering btw) the boards have a solderless breadboard style layout. This makes wiring easier for me and with extra connection spots it gives me the option of expanding the computer.

Progress has been slow

Well I've been slowly piecing the computer together here and there. My motivation has just been shot the last couple of days but I'm sure it'll get kicking soon. I do need to check the datasheet for the 2101 ram chips because two different schematics, the original and a version from Muller Labs, has two different pinouts for the chips.

Package came today

Well my package came today. Sadly I have finals all week. Hopefully this weekend I can finish my computer!

Package Beaming

I can't wait till the day we can beam packages directly from the send to the receiver. Little waiting. I'm just an impatient person I guess when it comes to the mail. Anyway, let's see some pictures of your unique Cosmac project?

BR1 Solderable Breadboard

BR1 at Jameco
These are the new boards I ordered. They are arranged like a regular breadboard. I got two of them because they are about 60 holes wide and the Elf would take 94 holes for all the ICs so it would leave room to expand. A separate board will be needed for the display unless I embed the displays into a case like the toggle switches. This layout would lead to a cool looking computer in my opinion. This would probably be a last resort if I can't get the other board running when the other parts arrive. I'm not very confident in my point-to-point soldering ability.

New parts ordered

Well I got my new switches ordered. While I was at it I also got some extra ICs and sockets just in case. I also got some neat perfboards with the same layout as breadboards. In the event I have to redo this thing I'm going to use these instead since they will make soldering easier. It won't look like the pictures in the article but I want functionality more so than looks.

Minor Set back.... well kinda a big one

So all of the switches I got turned out to be momentary toggle switches and guess what? The momentary switch I got isn't a momentary switch. I dislike datasheets with more than one product on them. Anyway I have a majority of the connections solder so I'm going to order the right switches and some back up ICs just in case. I'm also going to spring for some wirewrap compatible sockets since I have to have a minimum order anyway. That way if something turns out not to work on the point-to-point soldered version I can try wirewrapping instead. I've tried my best to keep the wires as organized as I can but there is only so much you can do.

Last package of components have arrived!

My last package has arrived. I won't get time till tomorrow to start the project so while we wait how about I pose a question to anyone who might be reading my blog. What have you done with an 1802 processor? Any cool homebrew computers out there?

EDIT -
Hi, my internet is slow and won't load the comment text box so I'll reply here.
I don't plan to emulate but I would mind trying to interface the two possible to use the Propeller as a driver for a screen and keyboard.

I show up on Google!

Well this is going to be an off topic post but I show up on Google! I noticed it in my stats. If you type cosmac elf project I'm near the top and if you type in just cosmac elf I'm on the second page! Well for me at least. It might be different if you do. Sorry to sound boastful but I've never shown up on Google before!

Goals

Goals, we need them for most projects and homemade computers are no exception. So what do I want my COSMAC ELF to do? Well I don't plan on this being my last 1802 based computer so I plan to keep this one simple and stick with the original plans shown in the first article describing the ELF in popular electronics. I'm keeping it nice and simple since this is my first homebrew computer ever. I'm read about them and have an ok understanding of how to build one using a z80 but this will be my first actual attempt. Plus I want to keep it retro. Once I've built this one I plan on making one similar to a Kim-1 in operation or maybe make one using a Parallax Propeller to give me easier access to a keyboard, video, etc. I'm not sure yet. We'll just have to see how this project goes first. ;)

A cheaper source for 1802s

I found a cheaper source for 1802s than ebay. It's here at the Electronics Surplus I'm still looking for a source of pixie chips too. I've heard that Intersil which is the current producers of the chips can do runs of them but you have to buy in large amounts.

Ram chips and displays have arrived

Got two new envelopes from my purchases on ebay. My ram chips and displays have both made it safely to my home. Just waiting for my package from Jameco to arrive so I can get started.

A more true to the original emulator

Here is a java based emulator where you actually flip switches to program the computer
http://www.cosmac.szyc.org/

TinyElf

I was playing with this COSMAC ELF emulator a bit yesterday. It's really cool. You can set it up to show you the state of the processor as well as the contents of the ram.
TinyElf

Some resources

Here are some resources I've found.
Popular Electronics: Build the COSMAC ELF
A nicely done COSMAC ELF
A video of a COSMAC ELF operating
COSMAC ELF Homepage - Has some nice pictures in the gallery. Be sure to check out the documents sections for more info on the 1802!

Cosmac Elf Project

Well college is winding down and we are heading into summer. So I must ponder to myself, "What to do, what to do?" Well being a computer enthusiast I thought I'd do something with computers, being an vintage computer enthusiast I then thought, "Hey! I'll build an old computer!" I started looking around at homebrewing a z80 or 6502 computer, but I wanted to build something that has been built before not reinvent the wheel. So next stop was Briel Computers which has amazing Apple 1 and Kim 1 replicas. I did more searching for something even more retro and then came across the COSMAC Elf.

I've looked at this computer before but was always deterred by the fact that the processor, a RCA 1802, and ram chips, 2101 where a task to find. Well I checked ebay again and SCORE! Now I have the processor, ram, and hex displays on the way. Just went to Jameco.com and found all the parts documented in the Popular Electronics article as well. If all goes well this should be a 100% authentic replica of the original computer. If I get bored afterwards I plan to do the other expansions talked about in the collection of articles.

More to come soon!