1977 was a momentous year for the home computer industry. The Apple II, Commodore PET, and Atari VCS were all introduced. These classic machines became the founders of three revolutionary microcomputer companies that changed the world. Interestingly, the "brain" inside each of them was the MOS Technology 6502 microprocessor.The 6502 was designed by Chuck Peddle of MOS Technology in 1975, at the dawn of the microcomputer revolution. It was an elegant design; simple, yet powerful. Its simplicity made it the cheapest 8-bit microprocessor on the market, endearing it to bean counters everywhere. And its power quickly captured the hearts of design engineers. By 1977, Steve Wozniak designed it into the Apple II. Nolan Bushnell had it designed into his Atari VCS video computer system. And Jack Tramiel had it designed into the Commodore PET.
It's common to have some kind of "badge" for computer shows and hacker conventions. Since this is the 40th anniversary of these incredible machines, we thought it would be appropriate to make a badge using a vintage microcomputer. So, we built a 6502 computer on a Badge for this years' Vintage Computer Festival Midwest in Chicago IL on September 9-10, 2017!
The badge is a complete working 6502 computer, with RAM, ROM, LED display, serial port, and on-board BASIC. It's built entirely with vintage technology; no modern or surface-mount parts. Connect it to a terminal or computer, load a message, and the badge scrolls it across the LED display. Or, show off your BASIC or machine language expertise by writing something truly spectacular!
It was 40 years ago today
That computers taught the kids to play
With chips to make a new kind of game
And the world has never been the same
So let me introduce to you
The micro called the 6502!
We ordered a bushel of boards, and a passel of parts. Now everyone can have a real working 6502 computer, just like the pioneers of the microcomputer industry. Prices were kept low by scrounging for surplus and mining our junkboxes for parts. Profits will be donated to support VCFMW, which has been putting on this convention free of charge for years! Order now... supplies are limited!
News flash Aug 28, 2017: The "Buy Now" buttons were incorrectly calculating shipping. It seems to be fixed now. But don't worry; any excess will be refunded to your Paypal account. Correct amounts for shipping (as of this date): USA free, international $5.25 for a bare board, $13.50 for a kit or deluxe kit. Email for shipping on multiple orders.
April 10, 2017: [Lee] realized this is the 40th anniversary of the Apple II, Commodore PET, and Atari VCS. He was planning to attend this year's Vintage Computer Fair Midwest in Chicago IL, which is put on by the Chicago area Commodore Computer Club. He started brainstorming with Josh Bensadon and Daryl Rictor about ways to celebrate this milestone.
April 21, 2017: We came up with the idea of a "badge" with a real working 6502. Daryl had a minimalist design with a 6502, 1 RAM, 1 EPROM, 1 6850 UART, and 1 TTL "glue" chip. But that wouldn't do anything visible without a computer connected; so Lee figured out a way to add a minimal LED display for some "blinkin-lights". The idea of a "nametag" was born.
April 27, 2017: We figured out a way to eliminate the UART, by using the 6502's interrupt pin as its serial input, and one of the output bits for the LEDs as its serial output. That got the size down to something small enough to use as a nametag.
May 11, 2017: Lee has a circuit worked out with just 6 chips. Daryl built and tested it successfully. So Lee laid out a PC board. Josh chimed in, and offered to donate EPROMs and other parts to keep the cost down.
May 18, 2017: We contacted VCFMW, and they loved the idea! Looks like a real "wow" project for this year's show. So Lee ordered some prototype PC boards to test.
June 8, 2017: [Lee] The PCBs arrived, and of course I built one immediately. Everything fits! If you use a screw-machined socket for the EPROM, the 0.3" RAM hides under it just fine. NOTE: Be sure to install the RAM and EPROM backwards from the other chips!When "off", the RAM is powered, and battery current is so low it's hard to measure (on the order of 5-6 microamps). When switched "on", battery current is on the order of 8-10ma. The 2MHz clock is running, and the data and address buses show the 6502 is executing code. But there was no display activity, and no response to serial inputs.
June 10, 2017: [Daryl] Oops! The ROM code I sent was for my simulator, which had the I/O at a different address. I fixed it, and sent Lee a new copy.
June 12, 2017: [Lee] burned another EPROM, and IT WORKS! The default "Welcome to VCFMW 12" message scrolls across the LED display! You can see a couple photos of the Badge in operation at the top of this page, and a few videos of it here. Hoo Hah!
Power consumption is pretty good. It draws about 25ma average; 10ma min when most LEDs are off, and 40ma or so with many segments on. The nimh AAA cells I'm using claim they are 1800maH (though I doubt it). If true, they could run the badge for a few days. :-)
Problems: First, there's no hysteresis in the reset circuit (can oscillate on/off with a failing battery), and the low-battery threshold is too high. Second, once turned on, I can't turn it off! When I open S1, the 6502 stops during reset with A14=0, A15=0, and R/W=1. This tells the RAM to read. If any data bit from the RAM is 0, it pulls GND low (via the input protection diodes in the 6502 and 74HC273), defeating the open switch.
June 28, 2017: [Lee] Fiddling with the SIP resistor values can fix the reset threshold OR add hysteresis; but not both at once. So I redesigned the Reset circuit slightly. The failure to turn off problem has an easy fix: The "off" contact of the switch grounds the clock input to the 6502. This makes O1OUT high, disabling the address decoder to turn all memory off. This will be the rev.B "production" boards.
July 4, 2017: [Daryl] Here is my "final" version of the software, with all the source code and even a 6502 emulator for your PC to run it on. It fits nicely into a 16K 27C128. You can also burn it into a 32K 27C256 if you prefer. Features:LED display:
Aug 1, 2017: We're writing a manual for the 6502 Badge to document hardware operation, the Monitor commands, and LED control software. Here is the current version. The EhBASIC manual is here.
Aug 6, 2017: The rev.B changes tested out good, and are in the PCB layout. Production PC boards were ordered, and will arrive later this month. Parts are all ordered, and coming in; so we'll have plenty of parts kits in time for VCFMW. It's all coming together nicely!
Aug 25, 2017: Time to "shoot the engineers" and make this project PUBLIC! We are now accepting orders, and Paypal "Buy Now" buttons are added on the web page. :-)
Created 6/2/2017 by Lee Hart. Last update 8/28/2017.
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