Replica 1 Briel

The beginnings
In 2003 Vince Briel, working with Tom Owad, got the idea to design an Apple 1 replica. He looked at the Apple 1 circuit and took the easy parts: the 6502 and 6821, RAM, ROM.
The dificult part is the video circuit with hard to get parts and replaced that with a ATMega processor. He also added a PS/1 keybaord input and combined that with the parallel keyboard input circuit. The result was a functional replica of the Apple 1 on real hardware.
Vince then started Biel computers elling Replica 1 kits and assembled boards. Many revisions followed, hundreds were sold. The latest incarnation, the Plus, is still for sale, not by Vince who stopped in 2015, but by ReactiveMicro. The Brielcomputers support website and forums are still online.
My experience with the Replica 1 begin with the Replica 1 SE in 2007, the same period Vince made the Micro-KIM

What you can find here:

Some photos of prototypes of the Replica 1:

Vince Briel looking proud of the working prototype!

Apple 1 Replica Creation Back to the Garage
Tom Owad’s book on the Apple 1, the Replica, electronics and much more.

You can read the book online at Applefritter or buy a cheap PDF version.

On the companion Cd you will find an early PCB design by Tom working with Vince. Here the circuit diagram.

Apple 1 Replica design by Vince, drawn by Tom Owad

Micro-KIM RAM, EPROM and Expansion boards

Optional add-ons to make the Micro-KIM a real KIM-1, with the second 6530/32 and a 32K RAM card to give enough RAM to run real programs like KB9 Basic.

The expansion connector is made for this. With the expansion board up to four cards can be added.

A 40 pins male connector. Pin 1 is labeled on the board and is near the edge at the upper-left corner
of the connector.

Here he description of the expansion connector. Also see the Circuit diagram.

1 and 40 two pins for ground to give proper grounding to optional expansion boards.
2 VCC, this is a 5V signal which powers the circuit
3-14, 31-38 CPU address lines A0-A15 used to address memory or devices
11 R/W read/write signal. Low when writing, high when reading memory
12-15, 26-29 CPU data bus. Used to transfer data to/from RAM/EPROM or devices
16 Sync. This signal goes high during when an instruction is being fetched for the CPU
17 NMI. Non-Maskable Interrupt signal to the CPU. Active low to generate
18 DEN, Onboard memory decode Enable line.
Control the enabling of the onboard memory
19 IO3 is the pre-decoded signal for the 2nd optional 6532.
Attach to CS1 pin 38 on 6532
20 PHI1 Phase 1 clock signal. 180 degrees from phase 2
21 IRQ Interrupt request signal. Active low generates an IRQ.
22 PB7 is I/O port pin PB7 from 6532 required to complete cassette interface
23 SST Single step signal used to control CPU with single step
24 TAPE this signal is used to complete the cassette interface.
25 RDY used to stop the CPU in single step circuit
30 PHI2 phase 2 main clock signal to the 6502
39 RESET 6502 RESET line, when pulled low will reset the 6502


Circuit diagram of memory expansion

Second EPROM
The Micro-KIM is already prepared for a second 6532. The ROM for it is in place, the address decoding is also available. This card brings the second 6532 with the free I/O and timers to connector.

The revision I have needs a wire to connect the missing ground line to the 74LS04 (tip from azog, Silent Q).

Expansion motherboard

With two expansion boards, both quite essential as shown above and one expansion connector, is not enough.
So the expansion board brings the expansion connector to four connectors, just one on one connected.
As you can see on the Cassette interface for the Micro-KIM page this makes for interesting additions.
The expansion board can be placed in two ways. The first way iverhanging the Micro-KIM for a compact solution. Or hanging outside, which makes attaching wires to expansion boards less risky. Always take care of the right orientation of the expansion boards, notice the ‘1’ on the baords and the exapnsion connector on the Micro-KIM.


Cassette interface for the Micro-KIM

(information and design by Norbert).

Cassette interface for the Micro-KIM.

With small changes Norbert took the circuit described in the 3rd book of Elektor Junior computer. The +12 V problem he solved taking a LT1073 dc/dc converter to generate this voltage. Everything is working fine: Micro-KIM is connected to the soundcard of the computer to store and reload programs.

N39 is needed because there is not a port present or reachable on the Micro-KIM board, so it takes 1/4 74LS01. With a pullup resistor of 3k9 connect the unused inputs to +5V, so the whole thing will not oscillate.
For the +12 V generation a LT1073 CN8-5 was used. The diagram is shown on page 12 of (5V to 15V Step-Up Converter). It is important to use exactly the values of the resistors (metal oxid series) shown there. The LT1073 CN8-5 is presently still available for 4,20? at . They also have got the LT1073 CN8, but it did not work in this context. The no-load voltage measured at the output of the LT1073 is much higher (arround +40V) than the desired +12V. But with load it reduces to about +11.8 V and remains constant there. A 12V/1W zener diode protects the 12V output of the LT1073.

Build an Elektor Junior

Page on building now an Elektor Junior.
Two designs complete with PCB design (Bram Prosman), reports of a complete build ( Philippe Roehr, Philippe Roca).


Junior revival Bram Prosman

In 2018 Bram Prosman started with his Junior Computer Revival.

His story and the source of documents and image on his website, check there for updated files

I copied over here his 2.0, 2.1 and 2.2 designs of the basic Junior.

Memory map Junior Computer
1980 04 72 Junior Monitor
Junior Computer Monitor Listing

Junior Computer Monitor Original TASM source
TASM_32 for Windows 10, 64 bit

Version 2.0
Built and tested. Note the design flaws in Version 2.0, read this first!

Junior Computer Schematics V2.00
Junior Computer PCB BOTTOM V2.00
Junior Computer PCB BOTTOM V2.00 Gerbers

DISCLAIMER – Please note Bram has not tested yet the V2_1 and V2_2 PCB’s!

Version 2.1 and 2.2
Built and tested. Note the design flaws in Version 2.0, read this first!
Version 2.x added support for smaller push buttons instead of the rare and expensive original used Digitasten.

Junior Computer Schematics V2.1
Junior Computer PCB V2.1
Junior Computer PCB V2.1 Kicad design files
Junior Computer PCB Gerbers V2.1
Junior Computer Schematics V2.2
Junior Computer PCB V2.2
Junior Computer PCB V2.2 Kicad design files
Junior Computer PCB Gerbers V2.2

DIY Build a Junior

The design of the Elektor Junior is well documented in the Elektor articles, books and other articles like the KIM Kenner. In many languages, the archive here is as complete as possible, but you could see some pieces of information in only one language section. The hardware components for the most part are not exotic, especially for the time of publication.
The software in the form of (sources of) the ROMs and applications such as Microsoft Basic and even Operating systems like OS65DV3 is also easy to find.

So with all this information available it is no surprise to see modern versions of the Junior. Some try to stay as close to the original design, others just take the ideas and implement it in a more modern an d convenient way.

Some obstacles in building a Junior are:

  • the original PCB’s are only available as low quality magazine articles quality. And even then be careful, the original article mixed up front an back!
  • the EPROM for the Junior monitor is a 2708 UV EPROM. A very old hard to get part, hard to program and requiring power supplies like -5V and +12V besides to usual +5V.
  • the expansion card used a 82S33 PROM for the address decoding. Also an obsolete part and hard to program.

What designers can do:

  • design the PCB’s again. Kicad e.g.
  • replace the 2708 with an EPROM like the 2716 or bigger or an EEPROM like the 28C16 or bigger
  • use a GAL or discrete logic for the 82S33 on the expansion board
  • use a modern SRAM IC and increase RAM memory a lot
  • modify the address decoding to fit the modern ROM and RAM
  • obtain parts like the 6502, 6532 and 6522
  • replace the hard to get 1 MHz crystal with a can oscillator
  • simplify the power to +5V

Here are some examples of builds:


Lab-Volt manual scan

Thanks to John at the scan of this book is available, now stored on due to size.
See also the Lab-Volt page

The description of the trainer is in the book
Microprocessor Concepts and Applications
Publisher: Lab-Volt
Download here for

KB9 and OS65Dv3.3 Junior software

Philippe Roehr on KB9 and OS65DV3.3

With thanks to Philippe Roehr from France I present on this page how he got KIM Basic 9 and Ohio Scientific OS65D to work on the Junior

Junior build

Philippe has build a Junior system with at least a main board, an expansion board, 16K Dynamic RAM board expanded to 64K and a floppy controller.

It started with the Junior itself, followed by the expansion card, The monitor software PM and TM were tested.

Floppy controller, RAM card behind.

Junior KB9 Basic

Philippe started with the KB9 binary from the KIM-1 pages.
Philippe then applied the process outlined in the Elektor articles to adjust Basic to the Junior character I/O routines and also improved the speed by adjusting the now unnecessary code that took care of the ROR bug in early 6502’s.

Philippe transferred the binary to the Junior with Ed’s utility KIMTape, producing a KIM-1 audio wave file. The Junior accepts this format, a bit slow but only needed once. After seeing all was well, Philippe wrote the now optimized Junior KB9 Basic to audio wave file, and made a hex dump on the terminal. I picked up the dump, a captured text file form a a terminal emulator, and wrote a conversion program to produce a binary.

All the files here: archive with audio wave file, dump on terminal, binary and conversion software.


After building the Junior, having PM and TM monitor working well, KB9 Basic operational, the next step Philippe took was getting the operating OS65Dv3.3 operational.
He took the steps described by Elektor in the articles with some modern additions.

A Junior able to run OS65DV3.3 needs an expansion card,  a RAM card (his is 64K) and the Elektor floppy controller, which is identical to the OSI one (6850 + 6820 ICs)

Instead of a real floppy drive Philip used the hardware Gotek floppy emulator with the Flashfloppy firmware. And used the manuals images of, and the OSIHFE utility described in the OSI Web forum posts.

Elektor made a bootstrap eprom (ESS515 download here, source in Paperware 2) able to
* load OS65D (V3.1 or 3.3 as far as I know) from floppy
* give basic I/O capability (RS232 and floppy)
* manage hex display and keyboard
* modify OS65 for the hex display after the very first load to fully adapt them to the system ( about 10 bytes to modify)

Here the OS65DV3.3 disk image in native and Flashfloppy format ready to use.

During the second part of december 2020 Philippe added a real floppy controller and added the Ascii Video Terminal (new version of hackaday). With improved moter control of the floppy drive!

VDU board with OS65D

PMV for OS65D source checked by Philippe Roehr



The KIM Uno, designed and produced and sold by Oscar Vermeulen, is a very simple “open-source hardware” project that started out as a replica of the classic 1976 KIM-1 computer. Later, Apple-1 compatibility and a 6502 programmable calculator mode were added, plus a built-in ‘early 6502 software gems’ collection.
It costs about $10 in commonly available parts (board & parts without case or power supply), but provides a faithful KIM-1 ‘experience’. An Arduino Pro Mini mounted on the back contains all the logic and memory.

I have two versions: the ‘original’ and the later redesigned version, Software-wise the same, with on the top of the PCB room for power connector (GND, +5V or a 9V battery) and a slide switch. , I use them with an USB cable (the blue one of this page) for power and the serial interface provided.

The software already works on the blue pill STM32 or an ESP32, with manual cabling to the keyboard/display and I expect a new version of the PCB for the ESP32.

The software for the serial interface (you really need a good serial terminal emulator, like Minicom or Tera Term) can be used on any Arduino Uno. After power on  it delivers a simulation of the LED display or the real KIM TTY teletype interface (a bit broken in the current version).

All well described on the pages of Oscar and well worth the money for a ‘6502 SBC’ experience or a Cosmac 1802 with a small LCD.

The default serial output: an animated KIM display

Pressing control keys to perform ST and RS key

Press TAB to get into KIM TTY mode. Make sure to select on your terminal Local Echo and CAPS Lock. Read the KIM-1 User manual how the monitor operates.

The Apple 1 mode, fully functional.

Microchess adapted to serial

The Wozniak/Baum disassembler