Author: Robin Kearey

269 Articles

CRISS CP/M Provides Modern Hardware For A Classic OS

August 30, 2021 by 30 Comments

Today you might choose run Windows, Linux, MacOS or some other OS on your computer. Back in the 1980s however, you generally had little choice: a certain home computer came with a certain OS, and that was it. If yours was based on a Z80 processor, chances are it ran CP/M. While differences in hardware often made direct data exchange difficult, CP/M provided at least a basic level of software compatibility between various Z80-based computers. Although eventually supplanted by MS-DOS (which initially aimed to be compatible with CP/M), enthusiasts kept the classic OS running on old hardware throughout the 90s and even beyond.

[Igor] decided to make a 21st-century CP/M machine by designing the CRISS, a single-board computer based mainly on AVR microcontrollers. The CPU is a 20 MHz ATMEGA1284P, which imitates a 4 MHz Z80 through machine-code emulation. A pair of ATMEGA328s run the peripheral controller and a VGA output, so the CRISS can be used with modern monitors. True to its heritage however, the image is monochrome green-on-black, looking instantly familiar to users of Kaypros, Osbornes and other contemporary CP/M machines.

Software is loaded through an SD card that holds floppy images. The CRISS can directly run programs written for the Kaypro II and Robotron 1715 computers, although other platforms can be supported as well with a software upgrade. [Igor] shows it running programs ranging from the Turbo Pascal compiler to games like Xonix and Tetris.

Housed in a neat little case, the CRISS can communicate with standard PS/2 keyboards and serial printers. Even an Ethernet port is provided for those willing to experiment with network connectivity (a rare feature in the 1980s).

We love seeing modern retro builds like this; similar projects we’ve covered before include the compact ZZ80MB and the huge Z20X. Others have used different ways of running CP/M on modern hardware, such as booting it directly on a Raspberry Pi or emulating an Altair on an ESP32.

Universal Bio-Electrical Signal Amplifier Makes Reading Body Signals Easy

August 26, 2021 by 18 Comments

The electrical signals emitted by the human body tell us a lot about what’s going on inside. But getting those signals inside your microcontroller is not straightforward: the voltages are too small for most ADCs, and the ever-present 50 or 60 Hz mains frequency makes it hard to discern subtle changes. Over at Upside Down Labs, [Deepak Kathri] developed a universal biosensor interface called the BioAmp EXG Pill to make all this a lot easier.

Its name refers to the fact that it can be used for several different bio-electrical sensing applications: ECG, EMG, EOG and EEG, which deal with signals coming from the heart, muscles, eyes and brain, respectively. To enable such flexibility, the board has connectors for two or three electrodes, as well as solder pads to mount resistors and capacitors to adjust the gain and bandwidth. An instrumentation amplifier increases the strength of the desired signal while rejecting noise and interference.

The form factor allows easy connection to electrodes on one side and a data acquisition system on the other. Measuring just 25.4 mm long and 10 mm wide, it should be easy to integrate into any type of biosensing gizmo you can come up with. [Deepak] has made several demo setups, showing him using the Pill with an Arduino to measure his heart rate, detect eye blinks, and even control a robot arm using his own arm muscles!

The EXG Pill is an evolution of an earlier EMG-only project. We’ve seen several great ECG and EEG projects before, but is the first time we’ve seen one amplifier that can do them all.

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Game Boy Advance SP Case Mod Adds Battery Capacity And Modern Interfaces

August 24, 2021 by 5 Comments

While there’s nothing quite like running retro games on their original hardware, using older consoles in today’s day and age can be a hassle due to incompatibilities with modern chargers and headphones. [tito] and [kyle] worked together to update Nintendo’s Game Boy Advance SP with a whole bunch of new features, tightly packed inside a 3D-printed replacement backshell. (Video, embedded below.)

The original 600 mAh battery has been replaced with a 1600 mAh pack for several hours of additional screen time. A Qi standard wireless power module as well as a USB-C connector allows charging the battery without carrying the original mains adapter. A Bluetooth module enables the use of wireless headphones, and a 3.5 mm jack enables classic earbuds as well, a feature lost when the SP replaced the original GBA.

The new backshell fits exactly on the original console, making it about 10 mm thicker. Although this makes it slightly less portable, it is apparently more comfortable to hold for those with big hands. The new functionality is implemented using off-the-shelf circuit boards, connected together with flying wires that are soldered to the required points on the GBA’s circuit board. The original connectors and switches remain in place and functional, and the entire operation can be undone if you want to return the device to its original state.

Others have added USB charging to the original GBA, or even stretched that handheld to become twice as wide. But adding significant new functionality previously required replacing the handheld’s entire contents.

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