In 2021, the world's first microcontroller, the Intel 4004, turns 50 years old. Leading up to its memorable anniversary date, Erturk Kocalar of 8-Bit-Force introduced the RetroShield 4004 for the Arduino Mega. This shield lets you easily run real code on an actual Intel 4004 microprocessor.
We covered RetroShields in the past, specifically the MOS 6502 version. These shields use an Arduino Mega to emulate the support logic needed to turn a microprocessor chip into an 8-bit computer. (Well, 4-bit in this particular case.) RetroShields are a great way to do low-level programming on the original CPUs without wiring (and debugging) a breadboard full of 7400-series parts.
The RetroShield 4004 is similar to the previous versions. It accepts a real Intel 4004 IC, and the Arduino emulates the RAM and ROM. Kocalar did take this shield one step further by emulating the first commercial device to feature the 4004, the Busicom 141-PF desktop calculator.
As the story goes, Intel designed the 4004 microprocessor specifically for the 141-PF. One look at the calculator's chipset, Intel MCS-4 (Micro-Computer System 4-bit), seems to confirm this tale. The part numbers of the chips are 4001 (ROM), 4002 (RAM), 4003 (Shift Register), and 4004 (CPU)!
RetroShield 4004 emulates the Busicom 141-PF's RAM, ROM, keyboard, and drum printer. The code in the emulated ROM is the same instructions included in the original calculator. The Arduino provides an interface over serial, which acts as the paper tape of the hard-to-find calculator.
Since the shield needs a real Intel 4004 microprocessor, there is a bit of good news and bad news. The good news is that you can still find actual 4004 processors for sale on marketplaces like eBay. The bad news is that they carry a high price tag, even for the plastic dip packaging.
8-Bit-Force says they have something in the works. We look forward to hearing (and sharing) news of that development.
You can purchase the RetroShield 4004 from 8-Bit-Force's Tindie store for the creative price of $40.04. (It does not include an Intel 4004 microprocessor chip.) A great resource to learn more about the Intel 4004 is www.4004.com.