Schematic and BOM at https://github.com/rvl-system/rvl-boards/tree/main/serial-adapter

A Fully-Configurable DCC Dual Power Breaker - providing protection for two power districts. The design uses an Arduino Nano to allow all operational parameters to be set easily.

Requires one SN74LS158DR and one SN74LS32 (both narrow-body), one 33 ohm 1206 resistor, one 40 pin strip of turned machined pin header strip, cut into two 20 pin strips, one single-pin horizontal header for RA8 (J2), and one 40 pin socket.

Socket the PIA chip (6520) and right row of ramchips. Run a wire between all pin-1 pins on the right row of ram sockets and attach header plug (Dupont connector) for RA8 connection on module. Install 256k ramchips in sockets. Install module underneath PIA and attach RA8 wire from RAM socket pin-1. That’s it.

-Beginner-Friendly Through-Hole Resistors: Uses through-hole resistors (4.7kΩ) for easy hand-soldering and a slim profile.

-Official Hardware Guide Aligned: The trace layout is designed directly from the “DIY Wiimote Conversion (Using Clock Pin)” schematic on page 4 of the official OpenFIRE-Hardware-Guide_1.3.pdf manual.

-Optional 5-Pin JST Connector: Physical JST socket will fit inside the barrel shell (JST MX 1.25)

-Enclosure-Ready Geometry: Formatted specifically to seat right into RetroMidget’s Wiimote camera housing using standard dimensions from @slikvik55’s Lightgun3DParts repository.

-Zero Onboard Crystal Needed: Relies on OpenFIRE’s native pin-generated clock (CLK), omitting external oscillators.

-Direct 3.3V Power Line: Streamlined 3.3V power path supplied directly by a Raspberry Pi Pico.

https://github.com/mikoyv3/openfire-wiimote-cam-adapter

-Beginner-Friendly Through-Hole Resistors: Uses through-hole resistors (4.7kΩ) for easy hand-soldering and a slim profile.

-Official Hardware Guide Aligned: The trace layout is designed directly from the “DIY Wiimote Conversion (Using Clock Pin)” schematic on page 4 of the official OpenFIRE-Hardware-Guide_1.3.pdf manual.

-Optional 5-Pin JST Connector: Physical JST socket will fit inside the barrel shell (JST MX 1.25)

-Enclosure-Ready Geometry: Formatted specifically to seat right into RetroMidget’s Wiimote camera housing using standard dimensions from @slikvik55’s Lightgun3DParts repository.

-Zero Onboard Crystal Needed: Relies on OpenFIRE’s native pin-generated clock (CLK), omitting external oscillators.

-Direct 3.3V Power Line: Streamlined 3.3V power path supplied directly by a Raspberry Pi Pico.

https://github.com/mikoyv3/openfire-wiimote-cam-adapter

A board to convert the original NES controller for use with the Commodore 64.

The A Button = Fire, and the B button = UP (same as the direction pad).

Note: This is based on the NES64 board.

Level Control is Bourns 3306F

9V Battery Ripple Filter for Active Pickups

A tiny RC filter board that mounts on top of a 9V battery and removes the high-pitched whine that USB-rechargeable lithium 9V batteries inject into active guitar pickups (EMG and similar).

The Problem

USB-rechargeable “9V” lithium batteries are a Li-ion cell plus a small boost converter. At the very light load of active pickups (~160 µA for two EMGs), the converter runs in burst mode, producing a ~360 mV p-p sawtooth at roughly 8 kHz on the supply rail, right in the audible range. Under heavier load it switches continuously at ~1.2 MHz instead.

Active pickup preambs are micropower op-amp circuits biased from a half-supply divider, so supply ripple goes straight into the signal path and comes out of the amp as a steady high-pitched whine.

The Fix

A simple RC low-pass filter between the battery and the pickup power buss:

• R1, 1 kΩ: series resistor
• C1, 100 µF electrolytic: filters the ~8 kHz burst ripple
• C2, 0.1 µF ceramic: handles the ~1.2 MHz switching spikes

Corner frequency is ~1.6 Hz, giving roughly 74 dB of attenuation at 8 kHz. The ~360 mV of ripple drops to tens of µV, below the pickups' own noise floor. Voltage drop at 160 µA is only ~0.16 V.

Installation

1. Snap the board onto the top of the 9V battery.
2. Connect the board’s +V OUT to the pickups' red wires / +V buss.
3. Connect GND to the guitar’s ground bus.
4. Battery negative still goes to the output jack’s ring as usual.

Note: the preamps take a fraction of a second to settle after plugging in (RC time constant ≈ 0.1 s), so a small thump on plug-in is normal.

BOM

Notes

• Plain alkaline 9V batteries have no converter and don’t need this board.
• Works with any active pickup system that runs from a 9V battery.