Rev K4L 1802 Membership Card Kit


[rev K2 CPU] [rev L front panel]

Page last updated Aug 24 2022.This is the support page for the Rev K4 CPU / Rev L front-panel 1802 Membership Cards. The Rev L front-panel board has been in distribution since May 1 2022; the K4 CPU since June 2021 until July 2022. Rev L is a major revision of the 1802 Membership Card Front Panel.

The Rev L Front Panel includes a two or six-digit hex display with ROM decode. The DB-25 I/O connector on previous versions was removed from the Rev L front-panel to accomodate the display. But those signals are still available on the 30-pin header. For more information on the Rev L front panel and interrupt handling to operate it, check the Rev L Web page (Rev L CPU and Rev L front panel).

For those familiar with previous 1802 Membership Cards, Rev K4 CPU with Rev K Front Panel was in distribution up to late-April 2022. See the previous Rev K4 Web page for details. See the Chronological section for links to pages and documents for versions current and prior.

This Web page contains MANY Web links with support and use information; but there's more background about design changes on previous version support pages. Links to order and for more information are below.

The photo on the left is of the bare Rev K4 CPU board, photo by Herb Johnson. The photo on the right is a bare Rev L Front Panel board.

"For those just tuning in, the Membership Card Kit is a reproduction of the original Popular Electronics COSMAC Elf computer, but shrunk to fit in an Altoids tin! It works the same, and runs the same software." - Lee Hart, developer.

Prices, ordering, contact

How to order: Order the Membership Card via links from the 1802 Membership Card home Web page. The page has links to current and previous 1802 Membership Card version pages. It also has links to 1802 history, testing, hardware, software, and more.


Product documents
A quality kit for the beginner or vintage builder
Rev K4L features and options
Initial testing and programming
Rev K4L detailed description
Engineering & Change Data
Hardware and software and notes about them
Errors, corrections, mods
Chronology of Membership Card products & support Web pages
Prices, ordering, contact

Pages edited by Herb Johnson, (c) 2022 Herb Johnson, except for content created by Lee Hart and others. To report errors on this page, contact Herb at, an email address is on that page. - Herb Johnson

Product and documents

Documentation Rev K4 CPU and Rev L front panel:
The Rev K4 CPU/ Rev L front panel manual for May 21 2022.
See the Recent History section for links to these and earlier Web pages with documents.
Here's the link to the 2019 1802 cheat sheet . Gives the 1802 instruction set, I/O connections.

Why is this a quality kit for the beginner or vintage builder?

[edge view]

Small size, ordinary components, "how to assemble" manual for hands-on building. The front panel and CPU boards stack to fit in an Altoids tin. (Rev I stack shown.) The front panel cover board (optional) fits over the Altoids lid.

Only readily-available electronic parts are used (except the 1802) and are part of the kit. Most parts are from the 1970's "ELF" era. All thru-hole parts (not surface mount), for easy hand assembly. Assembly manual guides construction, part by part, with testing and debug information.

Quality printed-circuit board, easy to see, build and repair:
- quality USA-made PC board material, 1 oz. copper, wide 15 mil traces
- IC sockets as included have screw machined pins
- key chips tested before distribution to avoid counterfits
- white, legible "silk screen" text to identify parts and pin functions
- 60 mil large pads, 40 mil holes to fit larger pins or pin-socket inserts
- large holes and pads are easier to desolder misplaced parts without damage
- gives a 70's look to a 1976 processor kit

"On occasion, customers have put parts in the wrong places. They commented [to me] that they were amazed they could remove them without damaging the PCB." - Lee Hart June 2021

1802 M/S card, features and options with Rev K4L

Run with or without a PC. For the full product, no PC, external hardware, or any onboard program, are required for use. Front-panel runs, halt, loads by toggling switches and displays by LEDs - no software needed. These are same features as the classic COSMAC ELF; plus RAM, ROM and I/O options as described here. For the CPU alone, it can be operated by a serial link which controls a ROM monitor or a ROMmed BASIC. Or you can put your own programs in ROM, or download them into RAM via a ROM monitor.

8-bit input and output ports The CPU and Front Panel boards have a common 30-pin header. It supports 8-bit data in and out; power and ground; 1802 LOAD and RUN; and serial. These lines are also used by the front panel to operate the 1802 in "load" mode. Also they act as toggle-in and LED-out ports. With a Front Panel atop the CPU board, you could add another 30-pin header to the Front Panel to access the 30-pin signals.

In previous versions of the Front Panel, these signals were also connected to a DB-25 matching a "PC parallel port". Some people operated the 1802 MC from that connector, from an old PC parallel port or from a microcontroller. Check earlier version's documents for details and ways to operate these Membership Card signals. (On the Rev L front panel, space for the DB-25 is taken by several 7-segment numeric displays.)

serial interface operation via EF3 and Q with a TTL serial interface. A two-color LED shows serial activity on Q and EF3. Serial operation requires a ROM or program to support a "software UART" and to interact with the serial user. The TTL connector is also the +5V power connector and can be compatible with some USB-to-serial adapter cables and boards. Serial and RS-232 features were discussed in more detail on the Rev I Web page's "Engineering" notes.

stable clock frequency with 4.0 MHz ceramic resonator. Previous versions included a 1.8 Mhz resonator.

Low-power standby, nonvolatile RAM: Separating the CPU board from the Front Panel, or disconnecting the power connector, will put the CPU board into a "standby state", program halted and RAM contents saved by the supercapacitor. Save time is hours to days depending. "With the supercap, I can load a testing program into RAM, test an 1802, remove power, put in the next 1802, and power up. The test program is still in RAM and runs." - Lee Hart

RAM and ROM on one CPU board The K4 CPU kit comes with a .3-inch narrow RAM chip. A ROM can be installed above the narrow RAM. You can run the CPU board only, with a USB to TTL serial adapter on connector P5, and a ROM monitor with serial terminal support. Assembly and operation is described in the K4 manual.

Add a ROM monitor or BASIC: Lee Hart offers ROM files or ROMS for ROM BASIC and / or an 1802 ROM monitor, or a "diskless" operating ROM. See these on Lee Hart's sales Web page. Other monitors or programs, from Lee Hart or others, can be run from your own ROM or from RAM, see the software notes below.

How To order

To order: Refer to the Membership Card home page for the current ordering status. An email address and Web link takes you to developer Lee Hart for ordering and contact.

Your initial tests and programs

The kit manual will have test programs and debug information; ROM monitors and BASIC ROMs are also available. Also, see this document on Testing the 1802 Membership Card with small toggle-in programs. Basic operations of the front panel are described. There's more links about testing and use, under "features" on this Web page. Other links are to testing hardware Web pages and testing software Web pages are on listed on the home Web page. - Herb Johnson

Rev K4L detailed product descriptions

The 1802 Membership card set, consists of a CPU board stacked on a Front Panel board, with an optional Cover Board atop the toggles. Or, you can run the CPU board alone. Also, you can buy a prototyping board for your own circuits. You can buy ROMs for a monitor or for BASIC; or burn your own ROMs from images provided. You can buy the boards, or a kit with boards and parts; or partial kits. And, you can buy a Cover Board, a circuit board to cover the switches and lights of the Front Panel card. These are all sized to fit an Altoids tin box. All boards (except the cover) accomodate the CPU's 30-pin expansion connector, which is also a data and control interface to and from other TTL-class devices.

[Rev K4 CPU]

[Rev K4 CPU]

1. Membership Card Rev K4 CPU board:

Rev K4 CPU assembled by Lee Hart on right; left is the layout of the K4 CPU. See the Engineering section for specific changes from previous versions.

- 1802 microprocessor (option for 1804/5/6 which have no load mode).
- .6-inch 24-pin socket for 2K to 32K byte-wide RAM or ROM, selected by P3 jumpers
- dual-use of a 27C512 ROM, select one of two programs at power-up
- also .3-inch 24-pin socket under ROM/RAM for narrow SRAM or ROM. 
- supercapacitor to maintain RAM contents with power disconnected or /ON inactive
- HI/LO jumper select on board ROM/RAM for high or low 32K address space
- board cuts to select U8 as narrow ROM not RAM 
- K4 adds 6-pin serial/power connector P5 for one-connector to USB/power dongle
- diode to /CLEAR for power-on clear
- ceramic resonator for stable clock in full kit
- the usual 1802 I/O bits (Q, EF1-EF4, INT, etc.) and OUT4 IN4 decoded and buffered
- IN/OUT4, control, serial and power brought out to a 30-pin header (pins labeled)
- size: 3.5" x 2.125"
- power: 3.6-5vdc at several mA (current depends on clock speed, RAM & ROM chips) 

[Rev L front panel]

[Rev L FP build]

2. Membership Card Rev L Front Panel:

Rev L front panel bare board component side on left, as built by Lee Hart on right. (Note: the standard Rev L kit is sold with *two* 7-segment displays. If you want all six, ask Lee Hart. See the "mods" notes for details.)

- plugs onto the 1802 Membership Card 30-pin connector
- read/write to memory and I/O ports, and clear/wait/load/run programs with no PC, external hardware, or on-board program
- LEDs and toggle switches provide Elf front panel interface as follows:
-- 8 data output LEDs (memory reads and OUT4)
-- 8 data input switches (memory writes and INP4)
-- EF4 input pushbutton to load front-panel switch data
-- EF3 input LED to display serial input
-- Q output LED to display serial output
-- 6-pin serial/power connector P4 for use with USB-serial adapters
-- NEW 7-segment display:
---- hardware mode displays memory or OUT4 as two hex digits (two digits standard w/kit)
---- software mode displays six-character ASCII messages with appropriate software
-- NEW hardware timer for interrupts to display six hex/ASCII messages
---- See these engineering notes for discussion
-- All power, control, and I/O brought out to a labeled 30-pin header
- size: 3.5" x 2.125"
- low power consumption: 0.25mA standby, plus about 1mA for each LED on
- interchangeable with all previous 1802MC CPU and Front Panels cards

6-pin serial/power connector
- RX/TX GND and +5 volts compatible with some USB-to-serial adapters
- adds "idle" signal, could be connected to serial (TTL level) RTS line or a toggle switch.
- one pin is removed, to key the cable connector so to avoid a reversed connection.

[cover card] [cover card]

3. Membership Card Rev L Cover Board:

[Actual photo of board for hex-display when available. Version for DB-25 front-panel is shown.] The Membership Card Cover Board is a *green* PC board to cover the Altoids lid and mounts on the Front Panel board. The board has holes for the switches, LEDs, power/serial connector, and the hex display (or the earlier front-panel DB-25 connector). There's silkscreened white labels and a tinned copper shield on the back. Cut a large rough rectangular hole in the Altoids box, and solder or epoxy this board to the top to provide a neat finished front panel.


4. Membership Card Protoboard:

The Membership Card Protoboard is a PC board for prototyping and development. It mounts on the CPU board instead of, or potentially underneath, the Front Panel board. It's sold seperately from the 1802 M/S Card kit or board set. See this Protoboard Web page for more details.

5. Membership Card ROMs:

Lee Hart provides ROM images for monitors, BASIC and other programs. From mid-2021 Lee offers a ROM and RAM kit. Details and documents will be on Lee Hart's ordering Web page, get there by links from the 1802 Membership Card home Web page. Currently the ROMs available as images and/or as prepared ROMS include:
MCSMP20 series of ROM monitors with BASIC3;
Chuck Yakym's MCSMP Super Monitor plus BASIC3;
Mike Riley's Elf/OS diskless ROM with many programs.

How to Order

Go to my Membership Card home page for a Web link, to developer Lee Hart for ordering and contact.

Engineering & Change Data for Rev L Front Panel

The Rev L Front Panel is a major redesign from Rev K and previous revisions. Notes were developed by Lee Hart and edited & discussed with Herb Johnson. Described briefly below is the hex digit display. A manual is in development. - Herb

two/six-digit display, by Lee Hart, May 2022: The rev.L Front Panel adds places for six 7-segment LED digits. Two digits are provided with the basic kit.

A 27C16 EPROM is programmed to display a byte from memory or the OUT4 port as two hexadecimal digits. No software is required (just like the original Elf computers with their HP or TI hex-to-7seg displays).

To use six 7-segment digits, a scan clock and counter are provided. The scan clock generates an interrupt every 2.5 msec if transistor Q6 is added. The interrupt informs an 1802 interrupt handler to output data for the next digit. When the 6th digit is reached, EF2 goes low to inform the interrupt handler to start over at the 1st digit. The EPROM has both hex- and ASCII- character sets, which can be selected with a HEX/TXT jumper.

Here's further discussion about the Rev L hex-display. See a note below about "interrupt disable, use EF1" for testing a display handler.

The LEDs are red common-anode Lumex LDS-A3506RD displays (available from Mouser and other suppliers). They operate at 1ma each, so power consumption is 1/10th that of the vintage Elf displays. Lumex sells these in other colors.

Errors, corrections, mods

Various non-critical components in the kit, may have different values from the current or previous manual. Typically these are like pull-up resistors, or the super-capacitor, or some I/O logic chips. Look at the Engineering Changes for design changes. In this section I try to document errors and solutions, or useful changes after/during construction which are optional. Previous revisions each have their Web pages with manuals and other changes. - Herb Johnson

two-digits in standard kit "I didn't want to increase the price of the kit; so it comes with 2 digits so I could keep the price down. The digits are about $1.50 each. Extra digits are available from me or various distributors." - Lee Hart June 29 2022.

General: start up in ROM. Like other 1802 Membership Cards, you can jumper select the U2 ROM address to either "LO" 0000H or "HI" 8000H. If your ROM is at 8000H, you must toggle in a "jump 8000" instruction into low memory: C0 80 00 and then reset. If your ROM is at 0000H, on reset the ROM will start. "Read the fine manual" for details.

Display interrupt disable

First production of the Rev L front-panel has the display timer wired to /INT through Q6. But without interrupt handling software, those interrupts will crash software. Lee initially documented not installing Q6, to disable the timer interrupt. An alternative was to break the PC trace to /INT, and install a wire for convenient testing. Later production of the FP includs a jumper P9 to break the interrupt. Here's some means to install a wire for testing with /INT or /EF1.

Early May 2022: interrupt disable, use EF1 to test Initially there's no interrupt handler software available for the Front Panel to operate six digits. "It's my suggestion: disconnect Q6 from the interrupt line, connect it to EF1. Software could be written and debugged to respond to EF1. Then other software could be written to support interrupt handling. Then the two can be combined and Q6 connected to /INT." - Herb Johnson

June 11 2022: Rev L interrupt line disable jumper: "[On the Rev L front panel board] I added a jumper P9 between the /INT pin and the collector of Q6. Leave the jumper open, and no interrupts from the scan clock Q6. Short it, and you get the scan clock interrupts. There wasn't room to add an option to connect [the Q6 line] to /EF1, but that's a simple wire." - Lee Hart

If your Rev L front panel has no P9 jumper: Cut the trace from Q6 to /INT, near Q6 for convenience. You can bridge the cut, when there's interrupt-managing software installed. If you want to test/develop software, add a wire. Drill a very small hole near the /INT pin, to route the wire to the top of the FP. Solder a long wire at Q6 at the interrupt line. Use glue or wax to anchor the wire under the PC board. Then attach the wire on the top of the board, to /EF1 or /INT or neither as desired. - Herb Johnson

Other mods and changes

May 16 2022: installing 7-seg displays: "I put mine right against the PCB, but that makes it well below the Cover Card -- you have to view it straight on to see the full digits. Watch out when soldering them. The pads are really close together, so it's easy to cause shorts. On the next [bord production], I may stagger the holes, and have the builder bend every other pin left/right to gain space and raise their height above the board." June 11 2022: I also staggered the pins of the 7seg displays so they aren't as hard to solder. This will elevate them above the PCB as well."

I recommend spacing them a bit above the board. The leads are long enough that you could put a spacer between them and the PCB and then solder them. I suggest using a strip of cardboard." - Lee Hart

May 15 2022: transistor change: "I used up my [inventory of] FJN3303 pre-biased transistors. I will be using FJN3305 in the future. It's equivalent; it just has 4.7K/10K instead of 22K/22K base resistors. " - Lee Hart

May 4 2022: red lens For a red display cover for the Cover Card, Paul Schmidt wrote in cosmacelf "Lee, PRD Plastics has some small red lexan windows, Digikey stocks them ..." Lee Hart replied: "Aha; thanks Paul! It looks like Digikey #PRD180R-ND [PDR 6201030, Red Lens for 1.8" Bezel] would work. It's red, 1.87" x 0.87". The DB25 holes [on the front-panel card] are 1.85" apart, and so just catch the width. The height is just right to cover the obsolete "PC SERIAL/PARALLEL PORT" text. About $2 each, or half that for 100."

Apr 4 2022: Build up the rev.L Front Panel board:

1. Space the 7seg LEDs up off the board to the same height as the switches. If you install a Cover Card, the opening for the old DB25 matches the 7seg LEDs, but you can't view them (except straight on) unless you space them up off the board.

2. I think I'll change the 7seg LED series resistors to [220 ohms from 100 ohms], as right now they are brighter than the individual LEDs.

3. Don't install Q6 (which generates 1802 interrupts from the Scan clock). It's not needed until we install a program that actually writes something useful to the 7seg LEDs. - Lee

Apr 2022: Access to 8-bit I/O ports, without DB-25

[Previous versions of the 1802 Front Panel had a DB-25 connector to the CPU's input and output I/O ports, 1802 signals, serial signals. But] all the signals that were on the DB25 are still on the 30-pin header.. The Front Panel [PC board] has two rows of holes. So you can install a 30-pin male header on the Front Panel to provide access to them." - Lee Hart, April 2022

Hardware and software and notes about them

This Web site has dozens of Web pages about hardware, software, operation and upgrades and debugging of the Membership Card. Please, please look at the Home Page of the 1802 Membership Card for links to those notes. Collections of hardware note Web links and software note Web links are on these linked pages.

FTDI USB to TTL: Here's operation of the Rev J M/S card with BASIC 3 and an FTDI-chipped USB serial adapter. Some details and history of BASIC 3 and USB serial adapters are below.

June 2021: Diskless Elf/OS ROM available Diskless Elf/OS ROM by Mike Riley gives you a taste of everything! It has Tiny BASIC, FORTH, Lisp, VTL2, a monitor, simulator, a mini-editor/assembler, and XMODEM upload/download. See links to the 1802 Membership Card sales page to get the binary ROM image and find more details.

2018: Lee Hart and Chuck Yakym provide a BASIC, Tiny BASIC, and ROM monitor, as binary images you can download to burn into a PROM. See Lee's 1802 M/S card sales page, look under under "BASIC for the 1802". Choose the "Rev J" version for your rev J CPU board. Details are in the ZIP files and on his site. There may be in-development versions on the cosmacelf Yahoo Web site in the "files" section, "Basic 3" folder by Chuck "the-eagle". again, choose "Rev J".

June 2017: Many people use a USB to serial adapter to operate the 1802 Membership Card serial port. Over time, it's been discovered that these adapters introduce hardware buffering of characters sent and recieved. This buffering interferes with timing delays caused by 1802 software, and delays deliberately added by "terminal" programs on the PC in use. Here's a Tech Note which is from discussion of these issues, taken from the cosmacelf Yahoo discussion group. - Herb Johnson

June 2017: Many people want to use a USB to serial adapter to operate the 1802 Membership Card serial & power port. Check the Rev I Engineering notes for some considerations about the power/serial connector.

These USB devices require "software drivers", which aren't always easy to install and use. Different USB "chips" give different results. Over time, it's been discovered that these USB-chip adapters, introduce hardware and software buffering of characters sent and recieved. This buffering interferes with timing delays caused by 1802 software, and delays deliberately added by "terminal" programs on the PC in use. Here's a Tech Note which is from discussion of these issues, taken from the cosmacelf Yahoo discussion group. - Herb Johnson

To order: Refer to the Membership Card home page for the current ordering status. Web links there take you to developer Lee Hart's Web site for ordering and contact.

Recent History of 1802 Membership Card production.

The 1802 Membership card has had many design changes: to improve operation, provide more user options, or to correct problems. Review previous version's support Web pages for discussions of those changes, or for guidance about use of the current version. Consider buying a new-version CPU or front-panel card versus modifying your version. There's often links to notes about such "mods" on the previous support pages.

May 2022: redesign to produce and distribute Rev L Front Panel. Rev K4 CPU is still in distribution. see the Rev K4 Web page for details on the previous K Front Panel.

Dec 17 2021: improvement to the Rev K4 CPU kit include a 4.0Mhz ceramic resonator, machine-pin low-profile sockets.

June 14 2021: Rev K4 CPU is in distribution with Rev K front panel. Several small circuit changes made, see the K4 Web page Engineering section. see the Rev K4 Web page for details.

June 2021: Diskless Elf/OS ROM available Diskless Elf/OS ROM by Mike Riley gives you a taste of everything! It has Tiny BASIC, FORTH, Lisp, VTL2, a monitor, simulator, a mini-editor/assembler, and XMODEM upload/download. See links to the 1802 Membership Card sales page to get the binary ROM image and find more details.

Sept 2020: Rev K3 CPU was in distribution until June 14 2021. Sold with Rev J front panel until Jan 2021; or with K front panel later. Rev K3 CPU changes U7 from 74HC374 to 74HC273. The Rev K front panel adds labels on its 30-pin connector. See the Rev K3 Web pages for details.

For earlier version of the 1802 Membership Card, Check the 1802 M/S Card home page, for links to ALL previous version Web pages. Further details of production and change history are on a history of production Web page.

40 years ago as of 2018, Lee produced an 1802 single board computer called BASYS. Look at the BASYS manual for hardware interface suggestions for the Membership Card.

How to Order

Refer to the Membership Card home page for the current ordering status. A Web link takes you to developer Lee Hart's Web site for ordering and contact.

This page and edited content is copyright Herb Johnson (c) 2022. Contact Herb at, an email address is available on that page..