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Raspberry Pi Soft Power Controller – The Circuit

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. Hackster.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.

Hackster.io Project Page   GitHub Repo
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Blog

Share projects on one of these 4 platforms

share projects

Sharing is the maker community’s foundation. When you share projects with others, you contribute to the community. In the past, you might just post your project on a personal website. Today there are many options to share projects.

This weekend I “finished” my reflow oven controller, Open Vapors. Believe it or not, five years ago there were not a bajillion similar projects. In fact, I based my design on the only completely open source project I found. It is a reflow oven controller Arduino shield from Rocket Scream.

After completing my controller, I was excited to share the project. Then I started to think about where to post the files. Obviously, here at baldengineer.com is one option. But I wondered. Is there a better place where others could benefit from my work?

This post is a few notes on the platforms used to share projects. At first, these might seem like they all serve the same purpose. From a high level that is true. However, there are small differences that you should consider when you share projects with the open source hardware community.

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Arduino

Detect short and long button press using millis

detect short long button press using millis

To detect a short and long button press using millis can give your project more functionality without adding more buttons. In this line-by-line example, I show how to react to a user pressing a button for a short period (100ms) or a long period (over 500ms). My example changes the blink rate of an LED on short presses. A long button press turns off the LED.

In the code, I make use of a struct so that a single variable can be used to track multiple parameters. The benefit of this method is that adding multiple buttons is easy. You could create an array of these tyepdef’d variables.

Download At GitHub
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Blog

7805 is at the heart of a Super Famicom / Super NES

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.

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Blog

Best Sorting Resistors Method 

sorting resistors method

When you buy a grab bag of components, you might need to tackle sorting resistors. Here’s how I sorted some bags of random resistor assortments last week.

Objectives

Then method I use for sorting resistors achieves these objectives:

  1. Fewer Bins. It doesn’t take long to create a large matrix of resistor values. My resistor sorting method is relatively compact.
  2. Quick to find. When I’m building up a circuit, I don’t want to spend time sorting through a pile. Once I know the value I need, I find a single package and then look for a single color band.
  3. Works with 4-band and 5-band resistors. Let me be upfront: I *hate* 5-band resistor color codes. While the 5th ring is supposed to be slightly offset, or wider, or a different type of color; it doesn’t matter. It’s nearly impossible to tell read a 5-band resistor color code when they are in a pile. However, using my method for sorting resistors, it doesn’t matter if I’m looking at a 4-band or 5-band resistor. I can immediately identify the resistor value.

Based on #3 alone, you might be wondering what is the fantastic method (and how much will it cost to get it!) Here’s the basics of my method for sorting resistors. (For FREE!)

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