1977 was a momentous year for the home computer industry. The Apple II, Commodore PET, and Atari VCS were all introduced. They became the founders of three revolutionary microcomputer companies that changed the world. Interestingly, the "brain" inside each of them was the same 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 Chuck Peddle designed it into the Commodore PET.
It's common to have some kind of "badge" for computer shows and hacker conventions. There are even Vintage Computer Festivals (VCFs) for fans of classic computers, held in various cities around the world. 2017 was the 40th anniversary of these amazing machines, so we thought it would be appropriate to make a badge for VCF shows using a vintage microcomputer.
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 your own programs to do 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!
(...my apologies to Sgt. Pepper's Lonely
Hearts Club Band and the Beatles...)
We ordered a bushel of boards, and a passel of parts. Now YOU 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. Order now... supplies are limited!
News flash: I'm almost out of the 7-digit 7-segment LED displays. Unless I find a new source, there are less than a dozen badge kits left (as of June 22, 2018).
April 10, 2017: Lee Hart realized that 2017 was 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 retro LED display for some "blinkin-lights". The idea of the "6502 badge" 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 LED output port bits as its serial output. Software would "bit bang" the serial data. That got the size down to something small enough to use as a nametag.
May 11, 2017: Lee worked out a circuit with just 6 chips. Daryl built and tested it successfully. So Lee laid out a PC board. Josh chimed in, and donated the EPROMs, USB-serial adapters, 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: The PCBs arrived, and of course were built 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 a few 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 was for my simulator, which had the I/O at a different address. I fixed it, and sent out new copies.
June 12, 2017: [Lee] burned an EPROM with the new code, and IT WORKS! The default "6502 badge for VCF..." message scrolls across the LED display! There's a GIF 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 about 50ma with many segments on. The nimh AAA cells I bought claim they are 1800maH; but actually measure more like 600maH (gotta love that fleabay marketing hype).
Rev.A problems: There's no hysteresis in the reset circuit, so it can oscillate on/off with a failing battery. The low-battery threshold is too high. Second; once turned on, I can't turn it off! When I open S1, the 6502 stops in 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 made O1OUT high, to disable the address decoder and turn all memory off. This became the rev.B "production" board design.
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've written 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.
Sep 9-10, 2017: Showtime! The badge was a hit at this year's VCFMW show. We sold every kit we had in the first hour! We have more boards, so I've been madly ordering parts, making up more kits, and sending them out as fast as I can. (If you're still waiting, hang in there -- it looks like we'll be caught up within the next couple weeks.)
Oct 2017: All the rev.B boards are gone. But folks from VCF Europa contacted me, and they also wanted badges. So I ordered a new rev.C batch. The VCFMW-specific text was removed, and replaced with generic VCF text. These went to VCFe in Germany and VCFe-CH in Switzerland.
Nov 2017: The rev.C boards have one new trick: The "R" jumper option lets you to use either the Rockwell R65C02 or the Western Design Center W65C02. The Rockwell part is only available surplus; but the W65C02 is available new from various distributors (for example, http://www.mouser.com W65C02S6TPG-14 for $6.95 each). I tried one, and it works! Note that the slowest W65C02 available today can run as fast as 14 MHz!
Jan 2018: It looks like the badges will be available at VCF-E in May. Jeff Galinat plans to have some for sale at the show. If you're there, look him up and say "hi" for me. :-)
Feb 2018: Oops... There's a little bug in the EhBASIC RAM sizing routine. If the "V" (version) monitor command shows a date of 5-27-17, don't press (enter) to auto-size RAM when you cold-start BASIC (with the @ command). It still works; but comes up with the wrong value and you won't be able to warm-start BASIC (with the # command) to retain a program in RAM.
Instead, type "2048 (enter)" (with a 2K RAM) to set the memory size. Auto-sizing still works if you upgrade to a 32K RAM. In this case you can either type "32768 (enter)" or just (enter).
Daryl made a new version of the ROM to fix this bug. If the monitor "V" command shows a date of 2-24-18, you can just press (enter) to auto-size RAM when starting EhBASIC with the @ command. Or, manually enter a size if you want to keep some RAM "private" for your own use.
Created 6/2/2017 by Lee Hart. Last update 6/22/2018.
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