Engineering check gear appears to have a really lengthy product lifecycle. Gear from previous many years continues to be in use in lots of tech firms’ labs and can be starting to work its approach into house check bench setups. That is due partly to the wonderful building of those units however many instances they nonetheless present all of the performance wanted to design and check cutting-edge circuits. One of many widespread duties a consumer might come throughout when doing design or check is the necessity to seize screenshots from these units for documentation functions.
Sreenshot taken utilizing a cellphone (📷: tomverbeure.github.io)
For older gear typically solely two strategies will exist: a consumer can dig up or buy an previous floppy drive to insert into the machine and save a picture, or the consumer can take an image with their telephones. Whereas each will suffice, they’ve their drawbacks as properly — to not point out, utilizing a floppy disk will virtually actually require a USB to floppy drive to be useful. One engineer by the title of Tom Verbeure determined to try to seize the display screen knowledge by hacking the parallel printer port on these older units.
The parallel printing port was the “USB port” of early computing units. It used a handful of management indicators and eight knowledge paths to ship info in parallel throughout cables. To hack this port, three key elements are required. This features a DB-25 connector to connect with the instrument of curiosity, a USB connection to ship the information out to a PC, and a microcontroller to deal with the information capturing and dealing with. For the microcontroller, a Raspberry Pi Pico was chosen attributable to its availability, low price, and ease of use. As well as, a stage shifter additionally needed to be included to interface the 5.0V parallel port voltage ranges to the Pico’s decrease 3.3V tolerant GPIO pins.
Schematic used for parallel port capturing software (📷: tomverbeure.github.io)
The schematic and PCB have been created utilizing KiCAD and are comparatively easy. Check pins have been additionally included within the design to assist capturing bus indicators to help with debugging and testing. Whereas the consumer mentions all the things works nice with the primary revision of the machine, a second one was made to make some optimizations. These included decreasing PCB layer rely from 4 to 2 layers, which helps cut back total price and decreasing the shape issue to avoid wasting house when in use. Each of the Gerber information for the PCB revision could be discovered right here.
PCB rendering of the primary revision (📷: tomverbeure.github.io)
Firmware is obtainable for the microcontroller programming, which consists of machine configuration and an interrupt routine to seize and ship the printer knowledge by means of the USB port. Moreover, Python code has been written to help with the information capturing occasions. Though it’s attainable to seize the uncooked knowledge utilizing the machine alone, the Python code gives a extra easy technique of doing this by routinely splitting print captures into totally different information and offering suggestions on the information being obtained.
Total, not many options exists for a handy means to seize screenshots on previous check gear. At present there are some units that exist such because the Retro Printer Raspberry Pi HAT. Nevertheless, this machine prices over $100 and the Raspberry Pi that can be wanted for it could not even be obtainable in as we speak’s market. Consequently, why not try to construct your individual? For round $30 and a day’s price of time, you could be capturing display screen pictures on previous check gear without having for USB flash drives.
