Raspberry Pi Soft Power Controller – The Circuit

Part 1 Control Rasp Pi power with an Arduino-based controller

The RetroPie project enables retro-gaming with a Raspberry Pi. All of the Pi models have enough computing power to emulate the major 8-bit and 16-bit computers of the 80s and 90s. With the Pi 3 I have even been able to play PS1 games with no problem. My current project is to put my Raspberry Pi running RetroPie into an old Super Famicom (SFC), or SNES, case. The catch? I want the original SPST power switch to work. And by work, I mean allow the Raspberry Pi to shutdown properly when the switch goes into the off position.  To accomplish this task, I am building a Raspberry Pi soft power controller.

Raspberry Pi Soft Power Block Diagram

Here’s a block diagram of the power controller. The basic blocks in a Raspberry Pi soft power controller include the LDO, a switching supply for the Pi, an AVR-based microcontroller, and the Raspberry Pi. This post will describe each of these hardware blocks.

One design objective was to draw as little current as possible when off. For my RetroPie, I will not be running on battery. However, I do not like the idea of wasting energy when something is turned “OFF.”

This overview is a multi-post write-up. This first part is on the hardware. In the next post, I will explain the AVR’s firmware. Later, I will come back to the Raspberry Pi side of the project.

Last week’s post was on Project Sharing Sites. I’m using two for this project. Hackaday.io will host the build log while GitHub has all of the design files. And by all of the file I mean the schematics, firmware, laser cutter files (soon), and Raspberry Pi code.

Hackaday.io Project Page  GitHub Repo

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7805 on a SNES Motherboard

When I made the AddOhms Tutorial on Linear Regulators, I made a comment about the 7805. I said it may be one of the most important Integrated Circuits (ICs) ever made. That’s a bold statement. The 555, 805,  or 7400 might all qualify for such a distinction. My feeling about the 7805’s importance is because it is a chip that is still popular today. It is used, or at least was used, in so many applications. And it is the heart of many 5V digital systems.

Including the Nintendo Super Famicom (and I assume the US SuperNES).

This picture is from an SFC I disassembled to repurpose the case. While taking it apart, the 7805 caught my attention because it was attached to a shield as a heat sink. Also, I find it fascinating that it is one of 3 or 4 through-hole components on the entire system. As you can see from the picture, it needs some cleaning. I might post more pictures later.

Wolfenstein 3D on Gameboy Color


Wolfenstein 3D defined the FPS genre in a way no one could have predicted. Just like the Gameboy defined portable gaming in a way no one could have predicted. Cartridge based computing and gaming offered something that disk (or disc?) based media never could: additional hardware.

The most famous example of additional hardware is the “SuperFX” chip that debuted with the SNES game Starfox. (It was in used in others in addition to a successor.) Most NES cartridges had other hardware too: mappers, sound generators, additional ram, etc. (more…)

Check out the 240p Test Suite


Learned about it in this video from the YouTube Channel My Life in Gaming. Some of their videos are a bit more technical than the general “retro review” style, which is why I started watching.

In their RGB 300 Video Series, they covered a homebrew project called “240p Test Suite.”

This project includes a number of test graphics and patterns to help in adjusting the settings of a modern TV. Even more impressive are the systems it covers:

  • Nintendo Wii
  • NSuper Famicom / SNES
  • Nintendo GameCube
  • Sega Mega Drive (Genesis)
  • Mega CD (Sega CD)
  • Sega Dreamcast
  • PC Engine (TurboGrafx-16) / PCE Duo

Check out this wiki page which lists all the tests and download it for your retro gaming platform.

CD-based systems are pretty easy to run since most of the era didn’t have copy protection. For the cartridge systems, you’ll need something like an EverDrive / SD Card reader for ROMs to make it work.

I’ve got mine on order…

Back in the 1990s, a 1.44mb floppy disk was a reasonable storage size for most documents.  For bigger documents or backing up an internal hard drive, other options were necessary. You might remember the Zip Drive, but that wasn’t the first large portable media.

The Bernoulli Box was the precursor to the Zip Drive. It used custom media that could store 10s to 100mbs on portable disks. Well, portable compared to carrying around an entire hard drive. Operating using the Bernoulli principal, the drive’s head never comes in contact with the “floppy” material inside the protective case.

Clint of Lazy Game Reviews takes a look at this cool forgotten drive technology in this video.

Using a learning algorithm known as NEAT, this Super Mario World play through is an example of a machine learning how to beat the level on its own. Using an evolutionary process, a neural network was built–or learned–to complete the level. The name of the program used to control Mario is called… Mar-I/O.

  • N: Neuro
  • E: Evolution of
  • A: Augmenting
  • T: Topologies

The initial play through is fascinating as well as the breakdown of what is going on. Well worth the 5 minutes.

[Update… Ryan in the comments provided this MarI/O version modified to factor in score.]

In the mood for some retro game music?  Check out D Wave’s YouTube Channel for a fresh take on some retro game tunes.  The PacMan melody is good.  You might also like his take on the SMB Theme.