Lee Hart's 1802 "Membership Card" development

Last updated Mar 14 2014. Edited by Herb Johnson, (c) Herb Johnson, except for content written by Lee Hart and others. Contact Herb at www.retrotechnology.com, an email address is on that page..


This page is about the design process of Lee Hart's Cosmac RCA 1802 microprocessor "membership card", from early discussions in cosmacelf in 2005, to his production of prototypes, to his Rev A prototypes of 2009; Rev B kits in 2010; Rev C kits in 2011; and Rev D kits in 2012. Current production is described and priced on the "membership card" home page. That home page also has links to software and hardware, notes and documents, and more resources.

On this Web page is a summary history of Lee Hart and his 1802 work, leading to the Membership Card, is below. Following that is an index of links to design discussions, documents, and developments; followed by prototypes and products by revision. The first half of the index is to seperate text and HTML documents elsewhere; the second half of that index, on prototypes and kits, indexes into information on the rest of this Web page.

There is some overlap between the "home page" and this design process Web page; this page will have mostly older material, the home page more recent material. There will also be a "current revision" or "current kit" Web page, as noted on both pages. As of July 2012, it's the Rev D kit Web page.

[assembled kit] Here's the assembled Rev A 1802 Membership Card, with a nickel to size it up.

A description of the prototype Rev A kit, construction by Herb Johnson and notes from Lee Hart, is on this linked Web page. See the Rev B the Rev C or the Rev Dsections below for their Web pages, manuals and schematics.

The current status of the 1802 Membership card, is on the Membership home page. Lee Hart can be contacted for details, see that Web page.My home page for my "retrotechnology" activities is at this Web link. Wander from there to other old computing interests.

- Herb Johnson

Summary history of Lee Hart and the "Membership Card"

[1802 prototype] A breadboard of the Membership Card circuits. Ode to Eight Bits, by Lee Hart

RCA developed the COSMAC CMOS product line in the mid-1970's, including the 1802 CMOS microprocesor and other support chips. In 1982, engineer Lee Hart designed and built an 1802 single board computer called BASYS. Lee Hart and I have been friends and colleagues since that time. Since the 21st century, he's become known for at least two things: electric cars, and the low-low-power COSMAC CMOS microprocessor from RCA, the 1802. Go to my Lee Hart Web page to look at some of those activities.

In May 2008, I found out that Lee Hart wanted to resurrect his old reduced FORTH for that board, which he called "8th". When I checked his activities, I found he was chatting back in 2005-06, about some kind of 1802 product in the Yahoo! 1802 and cosmacelf discussion group, with some of his 1802 colleagues from Dave Ruske's Web site Cosmac Elf. Lee created then, a small-card design for 1802 processor which he called the "membership card". It's built to about the size of an Altoids can. In April 2006 he had a prototype for the two stacked circuit boards needed; he completed the PC board layout by the fall of 2006.

But the design languished until 2009, when Lee was encourged to pick it up again. He produced a few boards and built a prototype. With my help and others, he revived his old "8th" language software, and discussed his work again with me and in cosmacelf. A list of board features is below. Here's a link to a early parts list, some operating instructions, and some initial design discussions.

In Oct 2009, Lee designed some prototype circuit boards for a small test run. By Nov, Lee produced a handful of circuit boards and distributed these to a few people. I and a few others assembled these cards and wrote about them: links are below. Issues were found with this design, and resolved during year 2010.

Meanwhile, by Jan 2010, with the help of cosmacelf members the 8th code was recovered from Lee's last paper listing.Details andlinks to source for 8th are on another Web page. Additionally, I (Herb Johnson) decided to look for a freely available 1802 cross assembler, in source form, that was close to the commercial (Avocet) cross assembler Lee used for his 1802 assembly, under Windows/MS-DOS. I found the A18 cross assembler and with the author's approval I've made that available: links are below.

By the summer of 2010, Lee was ready for a "Rev B" version of the Membership Card. The 1802 Membership card Rev B kit, is described on this linked Web page. The Rev B run was produced and sold from Dec 2010 through July 2011.

In early 2011, Lee made a few small changes to the Rev B layout, and added a third board as a front panel cover. He announced this cover in mid-July 2011, as he prepared to provide a Rev C kit and board set. The 1802 Membership card Rev C kit, is described on this linked Web page.

During 2012, Lee considered expansions for the Membership card, and discussed them with customers. The Rev D kit and design, released in July 2012, provides for stacking two CPU boards for RAM and ROM; expanding the output port to 8 lines and adding external power to the DB-25 connector; more address options for RAM/ROM and for I/O. The 1802 Membership card Rev D kit, is described on this linked Web page.

The current status of the 1802 Membership card is on the Membership home page.

From concept, to design, to prototypes, to kits

This section of this Web page, is an index into documents and Web pages which cover the whole development of the Membership Card, from early discussions and considerations to the latest kit. The early design process was discussed in the Yahoo! cosmacelf discussion group.. I've exerpted Lee Hart's posts at that time (with his permission) edited them into what amounts to his early design documents and discussions. This page indexes into that edited material in the links in the first few index sections below. Index sections about the prototypes and kits, link into details on this Web page which follows the index. Those details also link into many of the same documents. A shorter version of kit development information is also on the Membership Board home page.

The Membership Card Manifesto

  • Preamble
  • Proposition
  • A Thesis On Consumers vs. Makers, a 2012 tribute to Bob Rice


    Some of Lee Hart's early history is also in the summary above.

  • My Early Days and the 1802
  • The RCA 1802 and its competitors
  • Inspiration from the ZX81
  • Too "small"?
  • Languages; BASIC, FORTH, Logo?
  • LOGO


  • Genesis of the "membership card"
  • The ELF alternatives
  • The design emerges
  • Working the design options
  • Breadboarded and working
  • image of breadboard
  • Expansion
  • FAQ's on the Membership Board
  • Lee's note on debouncing toggle switches


    A complete summary of the above text, of what led Lee Hart to the Membership Card prototype.

    Prototypes to Production

    The links below are to text on this Web page, following this index.

  • Initial work 2006-2009
  • Rev A kits 2009-10
  • Rev B kits 2010
  • Rev C kits 2011
  • Rev D and later kits from 2012
  • Current revision kits

    results from prototypes and builders

    The following documents and Web pages were created from work on prototypes and kits.

  • a parts list, operating instructions, design discussions
  • I assembled my Membership Card!
  • P. Todd Decker tests his card and finds a flaw..
  • Testing and using the Membership card

  • Lee's operating instructions
  • Using the Membership card with a PC parallel port
  • Low power operation of the Membership Card
  • The OUT instruction and the Membership card
  • a single-step circuit for the Membership Card.

    Revisions, Availability, Status, Contacts

  • 1802 Membership Card product development timeline
  • current status of 1802 Membership card kits

  • Lee Hart can be contacted by email at [email addr] This is an image, not an email link.
  • Contact Herb at www.retrotechnology.com, an email address is available on that page.

    Prototype and kits for the Membership Card

    2006-2008 work on the Membership Card

    Lee Hart discussed his ideas about a "membership card" in the cosmacelf discussion group in 2006. See the linked "background" and "design" documents above for details. The material below is indexed and linked from the second half of the summary index above.

    April 2006 - Lee Hart: Ok, I've attached four versions of my "membership card".

    DEV2_06.PDF is the newest, and one I've laid out PC boards for. It is two boards, each about the size of a credit card, that stack and fit inside an Altoids box.

    LCD_06.PDF is kind of fun; it uses an 8-digit LCD display as eight individual "lights" to display the data bits D0-D7. For example,

    " 7 6 . . 3 . 1 . "
    means D7=1, D6=1, D3=1, and D1=1; the rest are zeros.

    MEMBER_06.PDF is the earliest design.

    DEV_06.PDF is the cheapest one, that uses DIP switches and bargraph LEDs.

    Note: Lee put these designs in the file archives of the cosmacelf Yahoo! discussion group. In Feb-Mar 2010 there's a discussion titled "Re: Membership Card - Ultra Low Power Variant". "Steve" (posting as aa3nm) wrote that he's taken the smaller version of Lee Hart's membership designs from 2006, and created a varient design and PC board. Those interested should access the cosmacelf Yahoo! site for more information. - Herb Johnson

    Oct 2006: status of Windows software?

    In June 2007 Lee told me privately that he has a PC board layout and is considering "investing" in some boards. In Oct 2007 he sent a image of the breadboard with this note on the back: "..finally got around to sending you a picture of my 1802 "membership" card. This shows the schematic, working breadboard, the mechanical model to check size/fit, and an Altoids box (which is what it fits in)." - Lee Hart

    Oct 2009 progress: prototype boards

    In October 2009, while discussing the price of 1802 processors, I encouraged Lee to produce a few "membership" boards. Here's a text file of our discussions about that, including a parts list. Concurrent with our discussions, there were discussions in in the Yahoo! cosmacelf discussion group about the ELF, and about 8-bit trainers in general:Here's Lee's discussion of that, with relevant exerpts from others. Concurrent with THAT in cosmacelf was a discussion of a serial-bus and PIC version of the ELF, Here's a text file of SOME exerpts from Lee from the serial-ELF (I call it SELF) discussion.

    Then, Lee posted as follows on October 9th 2009, in the thread "Microtutor II: a modern microcomputer trainer":

    A couple years ago, in a burst of nostalgic creativity, I designed a few ELF versions under the loose heading of "membership cards". The idea was to come up with a bare bones basic ELF design that was very inexpensive and easy to build. But sadly, I too suffer from "engineer disease", and kept dreaming up different features and versions so that no purchasable product came of it.

    The comments [in cosmacelf] have inspired me to dust off what I think is the best of these designs, and actually order boards for it. This is the DEV2 design in the cosmacelf files section. It's a 2-board set, with the ELF itself on one small PC board, and a separate front panel board with the switches, lights, and a parallel port interface for plugging into a PC.

    ELF Membership board
    - 3.5" x 2.15" (fits in an Altoids candy tin)
    - 1802 CPU (with adjustable RC clock oscillator)
    - one 28-pin memory socket (for standard 2k-32k byte RAMs or EPROMs)
    - 8-bit output port (OUT5 or OUT7)
    - 8-bit input port (IN5 or IN7)
    - expansion header with all I/O and 1802 signals
    - operates on 3v-6v at under 1ma (plus whatever the particular
    memory chip you use requires)
    ELF Front Panel board
    - 3.5" x 2.15" (plugs onto the Membership board)
    - 9 individual LEDs (D0-D7, plus Q)
    - 11 subminiature toggle switches (D0-D7, Clear/Wait/Load/Run,
    and Memory Protect -- exactly like original ELF)
    - 25-pin DB25 connector to go to PC parallel port (allows PC to
    completely control the front panel; and thus load, examine,
    and run programs, and read/write to the I/O ports).

    If this sounds suitable for what you want, let me know. I have to order at least 5-6 boards to get a reasonable price, and would like to find some helpers to test them before committing to a larger order. - Lee Hart

    This text file of our membership card discussions includes a parts list and some operating instructions.

    Oct 12: The cosmacelf list has continued to discuss itty-bitty micros and the membership board... I worked on the circuit of my Membership board some more. (I think) I've fixed the problem of keeping a program safe in RAM when the board is plugged or unplugged. I also fiddled with the layout some more, to add this and make a number of small improvements. I asked others on the cosmacelf list if anyone wants a "beta" board to play with, and have a few takers. So if all goes well, I'll order 5-6 boards on Monday. :-) - Lee Hart

    Oct 15: posted to the cosmacelf discussion group: "Hi gang, Herb Johnson is a friend of mine. He's been interested enough in the 1802 Membership card that he made a website on it. There are schematics and pictures of the breadboard, software for my 8TH (tiny FORTH), as well as comments gleaned from our discussions on the cosmacelf list. It's at [this Web page]. If you have any additions, corrections, or deletions, please contact me or Herb off-list. I ordered 5 sets of "beta test" Membership cards earlier this week with a 1-week turnaround. A couple people have expressed interest, so I'll probably send these first few out to get more "eyes" involved in debugging it. I ordered 5 sets of "beta test" Membership cards earlier this week with a 1-week turnaround. A couple people have expressed interest, so I'll probably send these first few out to get more "eyes" involved in debugging it. - Lee Hart

    Nov 1: Lee tells me he has the circuit boards and is assembling a unit, while obtaining a few more parts. The time-consuming part, he says, is drilling out the Menthos cover for the toggle switches and LED's.

    Nov 11 2009: Rev A prototype

    Lee Hart: I got the rest of the parts for the Membership card, and have the first one built. I started testing it this past weekend.

    1. The clock was running very slow.- It turned out that I had installed a 0.01uF capacitor at C1 instead of 100pf. But, the 100pf was a guess; the error gave me a chance to experiment. I settled on C1=22pf. Pot R1 give me a clock frequency adjustment range of about 14-341 KHz.

    2. High power consumption. - Even with the clock stopped, and no 1802 or memory, supply current was high; 24uA at 3v, and an amazing 4.67ma at 5v. It turned out to be the 1N5231B 5.1v zener at D11. Look at the current in 7 samples of this diode at voltage well below its 5.1v zener voltage:

       6-11 uA at 3v
      74-164 uA at 4v
     802-1734 uA at 4.8v
    2047-4703 uA at 5.0v
        >20 mA at 5.1v (its zener voltage)

    D11 is for reversed power supply protection (shorts the supply if you connect power backwards). And, it protects C5 (0.047 farads, 5.5vdc) from overvoltage.

    I did some looking, and there are much better (but more expensive) zeners. 9 samples of a 1N4690 5.6v zener measured:

     1-3 uA at 3v
      4-9 uA at 4v
      6-12 uA at 5.0v
      9-19 uA at 5.5v
       > 20 mA at 5.6v (its zener voltage)

    Unfortunately, the 1N4690 (5.6v) is a bit too high to protect C5 (5.5vdc). I'll have to order some 5.1v versions. For eample, the 1N4625 (5.1v) is $0.60 from Mouser. For now, I'm using the 1N4690 (because I have them.) With zener D11 replaced, the supply current (with an 1802 installed and running) is:

    VCC=3v:  3 uA at 0 Hz clock frequency
            22 uA at 14 KHz
           125 uA at 268 KHz
    VCC=5v: 20 uA at 0 Hz
            80 uA at 7.5 KHz
           305 uA at 341 KHz

    3. C5 leakage - Electrolytics have high leakage currents. Supercapacitors like C5 are especially high. I measured its leakage as 2.6 uA at 3v, 19 uA at 5v. That means that almost all of the supply current (at 0 clock frequency) is from this capacitor! - Lee Hart

    Nov 11, on cosmacelf discussion group

    I went back to work on it some more this evening. It had been sitting unpowered (or so I thought) for over 24 hours. it was last powered by a 5v bench supply that was unhooked when i was done.

    But I found that it was still running, off the charge stored in the 0.047 farad capacitor! Supply voltage was down to 2.3 volts, but the oscillator was still going, and the 1802 was still executing "air" on the data bus (there is no memory chip, so instruction fetches just read random noise on the data bus). - Lee Hart

    Rev A kits

    Jan 2010: Lee Hart has completed a few "membership board" kit sets, and distributed them to a few people. I recieved mine on Jan 25th.

    Feb 2010: I assembled my own Membership Card - check this Web page for details. My Web page about construction becomes the "Rev A" support page.

    Feb 25 2010:I've recieved inquiries about Membership card kits, so I asked Lee for his plans. He says: "Yes, [the emails are] encouraging! Thanks for forwarding their emails. I've been receiving them and responding. Basically, I'm saying that it's a work in process, so not to expect a perfect product yet. I only bought 6 boards, and 3 are left. I'll sell them the bare board for $35, or $75 for a parts kit like you got."

    April 2 2010: The six kits that Lee made are all sent out.

    June 2 2010: As of June 1st, Lee has constructed one, Herb Johnson (me) has constructed one, and also P. Todd Decker, who shared many notes and comments.

    July 2010: Todd discovered a problem with the OUT latch, which is solved by replacing the 74HC373 with a 74HC374. His discussion with Lee and Herb is on the Web page about his kit. The "fix" is on an accumulative Web page on revisions and additions.

    Rev B kits

    By the summer of 2010, Lee was working on a "Rev B" version of the Membership Card, including the fix to the Rev A described above. The 1802 Membership card Rev B kit is described on this linked Web page. The Rev B run was produced and sold from Dec 2010 through July 2011. Here's Rev A Revisions and upgrades to Rev B for the Membership Card; and here's Lee Hart's notes on his "Rev B" revisions to the Membership card.

    Rev C kits

    Spring 2011: Lee makes minor layout changes to the Membership card. He adds a third board, a cover board for the Altoids case, from a silk-screened and copper PC board. This will mount on the front of the Altoid can.

    mid-July 2011:, Lee has a few Rev B bare boards and a few Rev B kits of parts left. He ordered Rev C boards and parts for kits. The 1802 Membership card Rev C Support page is on this linked Web page. The Membership Card Product Sheetis a summary document.

    Aug 9 2011: Rev C kits and boards priced and available.
    Aug 15 2011: Rev C manual and schematics, photo of the cover card, are on the Rev C Support Web page.

    Jan 2012: Lee described ways to stack two Rev C CPU boards, to double up the I/O ports, and to provide both RAM and ROM. Essentially the CPU 40-pin lines extend the CPU signals to two CPU boards. See this Tech Note for details.

    Rev D and later kits

    July 10 2012: Rev D kits and boards priced and available until Jan 2013. Here's the Rev D & E support Web page. Changes from Rev C to D include customer options to change the I/O port address, to stack two CPU cards to double ROM/RAM and double I/O ports, and to provide 8 bits of output on the DB-25 connector.

    "Rev E" 2013 was announced in Jan 2013 and is out of production as of May 2013. Minor changes in PC board layout. Here's the Rev D & E support Web page.

    "Rev F" 2013 was announced in May 2013 and is out of production as of Feb 2014.Here's the Rev F support Web page.

    "Rev G" 2014 began in mid-Feb 2014 and the Rev G support Web page is at this link Serial and RAM/ROM options added.

    Most recent status:

    The current status of the 1802 Membership card kit, with prices, is on the Membership home page. - Herb Johnson

    Contact information:
    Herb Johnson
    New Jersey, USA
    To email @ me, see
    see my home Web page.

    This page and edited content is copyright Herb Johnson (c) 2014. Contents written by Lee Hart, are copyright Lee Hart (c) 2012. Copyright of other contents beyond brief quotes, is held by those authors. Contact Herb at www.retrotechnology.com, an email address is available on that page..