GOSHtastic - Game shows, Options, Software, & Hardware!

Modified 9/16/2014 Those of you who have programmed an Arduino through the Arduino or AVR Studio IDE may have noticed the utility that is really doing the work: AVRDUDE (AVR Downloader/UploaDEr).  This is a powerful program that can facilitate programming new sketches on top of a bootloader, load a brand new bootloader or chip image, capture the current firmware programmed on the chip, and set fuse bits (which can render your chip unusable without special tools if you're not careful). You mean I could have been doing this the whole time? The LEDgoes USB Communicator supports both programming over serial (bootloader must be present) or via ICSP bitbang (very slow).  The ICSP operation is identical to Adafruit's FTDI Friend product.  The serial programming is identical to the Arduino, except that in my case, I'd like to be able to program two ATmega chips at the same time without switching cables.  What's the best way to do this? My original train of thought ...

For the LEDgoes manufacturing & assembly stage, it would be desirable to simply secure each board to a programming jig, and the jig would be able to program both chips without hassle or confusion.  This means that we will need to insert a switching mechanism somewhere in between the ISP (in-system programmer) headers and the actual programming pins on the board so only one board at a time gets programmed.  I am quite familiar with digital logic, but don't have a knack for understanding other types of circuitry, so it struck me as a possibility to use some 74-logic to route the signals sent from the ISP to one chip at a time. The 7400 series of transistor-transistor logic (TTL) gates date back to the mid-1960s, shortly after the invention of the transistor itself.  Some chips in this series provide basic Boolean operations, others are counters or shift registers, and still others are flip-flops and latches (memory).  Over the last 50 years, this series has been ...