Breadboarded and working ------------------------ July 29 2005 I have it breadboarded, and it works. So the schematic is now pretty stable. I'm working on the packaging now, to make it all fit in an Altoids tin (the size of a credit card, and 0.8" high). It requires two PC boards that stack. The easier way to do it [would be] to put half the parts on each board, so neither board by itself does anything useful. The main board has the front panel switches, LEDs, input and output ports, and 25-pin D connector to a PC's parallel port. The second board is smaller (so it doesn't overlap the rather tall switches and D connector) and has just the 1802, RAM, and a couple "glue chips. The more difficult way (which is what I'm trying to do now) is to put the computer on one board (1802, memory, I/O port) and the front panel on the other (switches, LEDs, 25-pin D connector to a PC's parallel port). This way, the computer board alone is a functional "BASIC Stamp" type computer. But it requires keeping an exceptionally low profile on each board. Aug 10 2005 Sorry Craig, but I haven't gotten any farther on my design. I have it breadboarded on an EL socket, but have been struggling with packaging issues in laying out PC boards for it. I set myself a (rather arbitrary) goal of fitting it all into an Altoids candy tin. That in itself I can do (there are enough cubic inches). But it takes some awkward hand-fitted assembly tricks. So I keep brainstorming on ways to arrange the parts to make it also easy to assemble. Sep 27, 2005 I'm still plugging away at it! Here's the layout that I'm currently working on. Elf Membership board (CPU, memory, 8 bit I/O port, clock, reset, etc.): ___________________________________ / ______ _______ _________ \ | |_4013_| |74HC132| |_74HC373_| | | __________________ ____________ | | | | | | | | | 1802 | | 32k RAM | | | |__________________| |____________| | | _________ _________ | | |_74HC244_| |_74HC373_| | | ......................... | <- 25-pin male connector \___________________________________/ (0.025" pins on 0.1" centers) Front Panel board (switches, LEDs, D connector to PC parallel port): ___________________________________ / ____________________ _________ \ | | ______________ | |_74HC257_| | | | O \____________/ O | ________ | <- 25-pin D connector | |____________________| |_74HC32_| | | | | _ _ _ _ _ _ _ _ _ | |(_) (_)(_)(_)(_)(_)(_)(_)(_)| <- LEDs | Q RUN WR D7 D6 D5 D4 D3 D2 D1 D0| |(^)(^)(^)(^) (^)(^)(^)(^)(^)(^)(^)(^)| <- toggle switches |IN LD CLR RD | | ......................... | <- 25-pin female connector \___________________________________/ (on back of board) Each board is 3.5" x 2.125". The Elf Membership board is a self-contained single-board computer; it can be used all by itself if desired. The 25-pin header has power, ground, /EF4, Q, /LOAD, /CLEAR, /MWR /WE, 8 inputs, and 8 outputs. Depending on the RAM used and clock speed selected, it runs on 3v at about 200 microamps (that's over a year on two AA batteries). The Front Panel board has a 25-pin female connector on its back. It plugs onto the top of the Elf board. To actually get them both into an Altoids tin (13/16" thick), the space between the boards needs to be 5/16". This requires either very low-profile sockets on the Elf Membership board, or no sockets at all. Also, you'll have to work hard to keep the leads very short on the backs of the two boards. I plan to bend the leads over before soldering, and then rub the board on sandpaper when finished to knock off any high spots. All in all, it's like origami to fit it all in! But the actual component spacing on the boards isn't all that high. I'm trying to keep big pads on the solder side with no traces between pins to make it easy to solder. How does this sound? Oct 9, 2005 Hello, This email message is a notification to let you know that a file has been uploaded to the Files area of the cosmacelf group. File : /Membership Card/DEV2.PDF Uploaded by : leealanhart Description : Latest iteration of "Membership Card". Two board; one an 1802 single-board computer, the other an Elf front panel for it. Both fit in an Altoids box! You can access this file at the URL: http://groups.yahoo.com/group/cosmacelf/files/Membership%20Card/DEV2.PDF To learn more about file sharing for your group, please visit: http://help.yahoo.com/help/us/groups/files Nov 16 2005 That reminds me; I finished a PCB layouts for my membership card. I'm still tweaking, but it's very close. (I won't shoot the engineer yet; he's me! :-) The membership card is an 1802 single board computer, about 3.5" x 2.125", with the 1802, 2k-32k bytewide RAM, clock, reset, 8-bit input port, and 8-bit output port. It's optimized for low power, and runs on less than 1ma at 3v. The second board has all the switches, lights, and logic to make it function as a Popular Electronics "Elf". It also has a 25-pin "D" connector to connect to a PC's parallel port. The PC can run the Membership card via this port to read and write memory, reset, run programs, and watch all the I/O. The two boards stack together via a pin header, and fit inside an "Altoids" candy box to make a 3.75" x 2.25" x 0.8" pocket computer!Nov 17 2005 I assume you're looking at the DEV2 schematic at www.cosmacelf.com? That's very close to the version I laid out. All that's changed is that I added a 0.047 farad supercapacitor to maintain RAM without power, and various pinout changes to make it easier to lay out. U5A is used as a gate, not as a flip-flop. When an OUT5 or OUT7 output instruction is executed, U4 decodes it and makes the D input of U5A high. /MRD will be low during an output instruction, so the R input of U5A is low. Thus, when TPB goes high (in the last part of the bus cycle), U5A will "set" and its Q output goes high. This lets the data on the data bus from memory to be passed to the output port's outputs (U7, 74HC373). When /MRD returns high at teh end of the OUT instruction, U5A gets reset, its Q output returns low, and the output data it captured in the output latch U7. This peculiar use a of flip-flop is a consequence of having half a flip-flop left, but no gates :-) -- Feb 19, 2006 I traced out the [PC layout for the] CPU board schematic, and started on the keyboard/display board [layout], but then I got distracted by other projects. I'd be happy to send what I have to anyone for a stamped self-addressed envelope. Mar 30, 2006 ....My Membership card has 8 ultra-bright blue LEDs. They are the most amazing LEDs I've seen yet. At 100 MICROamps they are as bright as normal red LEDs at 10 MILLIamps. All LEDs on is still less than 1 ma.