• Case study for ESP-32_CoCo in a Patola PB-087 enclosure

    7 days ago • 0 comments

    I got interested in the ESP32_CP400 project and did a study to see if a version using through-hole components would fit inside a Patola PB-087 enclosure, which measures 96 mm deep, 72 mm wide, and 30 mm high at its thickest part.

    Here is the enclosure:

    For this study, I followed the original project. Although it doesn't include the full schematic, it features board images showing a few more 3.5mm jacks: two for the cassette recorder, one for audio, and one for an RS232 interface. I managed to fit three jacks, but it should be possible to add a fourth one, either by changing the jack type or by removing the power switch to make room for the audio jack next to the VGA connector.

    Original project board:

    Case study:

  • Yamaha YPVS controller schematics

    05/18/2026 at 21:36 • 0 comments

    This schematic diagram was reverse engineered around 2004 from the original modules my brother asked me to fix. I even posted it on some forums, which unfortunately were killed off by WhatsApp groups.

    At the time one of the major challenges was to figure out the internal configuration of the resistor networks which are non-standard types.

    The module is composed by an 8051ish microcontroller, an H-bridge, an ADC, a clipping circuit and a hardware watchdog circuit.


  • CP400 standard ROM cartridge (rev.eng)

    03/20/2026 at 00:30 • 0 comments

    Recreation of a standard ROM cartridge for the CP400 Color Computer,  a TRS-Color compatible manufactured by Prologica .  (Github link)

    The schematics and the board were reverse engineered from the pictures and article from Rafael Ferrari (thanks!) 

    I like to superpose the bottom and top pcb images to figure out the connections using Libre Office Draw. Other programs can be used as long as they provide to adjust the transparency of the images.

    I was intrigued by the bodge wires used on the original cartridge but after analyzing the schematics I could see no reason why the jumpers on the board were not used.

    The circuit uses a BJT with a speed-up capacitor on its base to form an inverter for the address line A13 that is used to select either chip is active. That was a very common trick in the 1980s to save on glue logic chips. While such components were not present on the board, it was easy to figure this out given the application.