Embedded computing

A simple and inexpensive shift register can be used to increase the digital output provision of a Raspberry Pi or microcontroller. This well-know technique is easy to apply, but has some limitations that require careful consideration.

Categories: software development, C, embedded computing, Raspberry Pi

This article is about using an I2C analogue-to-digital device for applications like reading sensor values or monitoring backup batteries. With all the technical bits left in.

Categories: Raspberry Pi, electronics, embedded computing, C

This article describes how to do simple temperature measurement with a Raspberry Pi, and I2C analog-to-digital converter, and a thermistor.

Categories: Raspberry Pi, electronics, embedded computing, C

Collecting sensor data, or low-level system status information, is a job that is often best done in C/C++. Distributing this kind of data to other system components in a way that is platform- and language-independent can be a challenge. This article suggests a way to do this use AMQP message distribution.

Categories: embedded computing, middleware

Although connecting a USB keyboard to an Arduino-type microcontroller without addition hardware can be tricky, there are no such problems with many 90s keyboards. This article is about giving new life to old keyboards, by using them as input devices for microcontroller projects.

Categories: Arduino, embedded computing, retrocomputing

Mapping keyboard keys to key codes on Linux is well-documented for the graphical desktop. But what about console applications on embedded Linux systems? There's not much documentation in this area.

Categories: Linux, C, embedded computing

Writing graphical applications for minimal and embedded Linux systems can present a challenge. One of the problems is producing nicely-rendered text without the facilities that a graphical desktop would provide. This article describes how to use the FreeType library to render text to the Linux framebuffer.

Categories: software development, C, Linux, embedded computing, Raspberry Pi

An oddity of the GCC C compiler that can lead to strange results, particularly in an embedded application

Categories: C, embedded computing

Using the official Raspian repository to assist the construction of a custom Linux for embedded applications is quick and convenient, compared to building everything from source. However, this approach has certain hazards.

Categories: Linux, Raspberry Pi, embedded computing

On websites, and in hobbyist kits for Raspberry Pi and Arduino, you'll often see I²C devices connected that have different supply voltages. This is (usually) safe and, in non-critical applications, tends to work. But why?

Categories: Raspberry Pi, electronics, embedded computing, Pico

This article describes how to generate and use compressed, anti-aliased font data, for use in a microcontroller application.

Categories: C, Linux, embedded computing, Pico

There are many kits and plans available for constructing miniature mechanical keyboards. But what do you do if you want a layout the nobody else seems to use? Build it from scratch.

Categories: Arduino, embedded computing, C

The absolute minimum information needed to start using the Linux framebuffer as a graphical display in C/C++ applications.

Categories: software development, C, Linux, embedded computing

This article continues my original framebuffer just the essentials article, by describing how to handle less straightforward framebuffer configurations.

Categories: software development, C, Linux, embedded computing

Using a single MOSFET transistor for power switching in microcontroller applications is simple and low-cost, but it often doesn't work as well as expected. Either the switched device doesn't run at full capacity, or the MOSFET gets hot. This article explains why.

Categories: Raspberry Pi, electronics, embedded computing

A series of simple, progressive examples that demonstrate the essential features of programming in ARM assembly language.

Categories: Raspberry Pi, software development, embedded computing, assembly

It's surprisingly difficult to detect switch actuations in a robust way, dealing with contact bounce and other quirks. This article describes one approach to the problem in C.

Categories: Raspberry Pi, electronics, embedded computing

The HC-SR04 proximity sensor is an inexpensive and widely-used ultrasonic device. Connecting one to an HC-SR04 to a Raspberry Pi is a common educational exercise, but getting accurate, repeatable measurement of distance in a real application is actually quite difficult. This article explains why, and what can be done to improve matters.

Categories: software development, C, embedded computing, Raspberry Pi

Many battery-backed power supplies for the Raspberry Pi, and similar systems, use the INA219 current/voltage monitor IC. This device has an I2C interface by which the Pi can determine the battery voltage and current, and estimate the charge level and run-time. This article describes how to write C code that interacts with the INA219.

Categories: software development, C, embedded computing, Raspberry Pi

In this article I explain how to construct, and program in C, an I²C interface to the popular HD44780 LCD display for the Raspberry Pi. Between the article and the accompanying source code, no technical details are concealed: I present the complete hardware design and every line of C code needed to operate it.

Categories: software development, C, embedded computing, Raspberry Pi

How to construct a custom networked storage (NAS) unit based on a Raspberry Pi and two mirrored USB hard drives -- and why you might want to.

Categories: Raspberry Pi, embedded computing

The Raspberry Pi doesn't offer much in the way of analog outputs, or even hardware controlled PWM. Software-controlled PWM is an alternative in some applications, but it needs to be used carefully, if inefficiencies are to be avoided.

Categories: software development, C, embedded computing, Raspberry Pi

This article is part of a series on building a customer Linux installation for a Raspberry Pi-based appliance. It explains how to install and set up the minimum software to get audio playback working.

Categories: Raspberry Pi, Linux, embedded computing

This article is part of a series on building a custom Linux installation for a Raspberry Pi-based appliance. It explains how to make a bootable SD card with Pi firmware, a Linux kernel, and a shell. It's about as minimal as a Linux system can be.

Categories: Raspberry Pi, Linux, embedded computing

This article is part of a series on building a customer Linux installation for a Raspberry Pi-based appliance. It explains how to obtain and install fundamental utilities for use in a system with a read-only filesystem, and no package manager.

Categories: Raspberry Pi, Linux, embedded computing

Introducing a series of articles on building a custom Linux installation for the Raspberry Pi, for appliance applications.

Categories: Raspberry Pi, Linux, embedded computing

Switching loads of an amp or two with a Raspberry Pi or a microcontroller can be accomplished using a small number of inexpensive components. Suitable circuits are widely published, but the details of operation are not always described.

Categories: Raspberry Pi, electronics, embedded computing

This article is part of a series on building a customer Linux installation for a Raspberry Pi-based appliance. It explains how to set up a system which hitherto only boots to a root shell, to a network-aware installation with service management.

Categories: Raspberry Pi, Linux, embedded computing

This is a design for a robust, wooden enclosure for a Raspberry Pi, battery power supply, and touchscreen, that can be made using hand tools.

Categories: Raspberry Pi, embedded computing, electronics

It's entirely possible to run simple, X-based applications in an appliance-based Linux installation: you just have to dispense with the graphical desktop and all its baggage. This article explains how.

Categories: Raspberry Pi, Linux, embedded computing

The Maxim DS3231 I2C real-time clock is a reasonably accurate, inexpensive device, that is easy to interface to the Raspberry Pi Pico.

Categories: C, embedded computing, Pico

This article describes how to construct a desktop photo clock using a Raspberry Pi Pico and some solder-free peripherals.

Categories: embedded computing, Pico

I've been using the Raspberry Pi Pico for embedded projects for the last two years or so. What do I think of it now?

Categories: embedded computing, Pico

The MAX7219 IC is widely used to control an 8x8 matrix of LED, but they can be chained to create much larger displays. This article describes how the chaining works, and how to create a driver for the Raspberry Pi Pico.

Categories: software development, C, embedded computing, Pico

A specific application of the Pico7219 library that I described in an earlier article.

Categories: embedded computing, Pico, electronics

This is the first of (at least) two articles on loading and running arbitrary executable code into RAM on the Pico, and running it.

Categories: C, embedded computing, Pico

This is the second of (at least) two articles on loading and running arbitrary executable code into RAM on the Pico, and running it.

Categories: C, embedded computing, Pico

The Pi Pico has USB host support, and can work with a USB keyboard. Although there are some programming examples, the general approach to programming USB host operations is not well documented.

Categories: software development, C, embedded computing, Pico

This is a versatile touchscreen display module with a strikingly low cost. But is it any good?

Categories: embedded computing, Pico

The Pi Pico is an impressive microcontroller for its size and cost, but it lacks specific non-volatile memory. This article explains how to use the program flash ROM for that purpose.

Categories: software development, C, Linux, embedded computing, Pico

Although building and deploying a simple program to an Arduino board is a point-and-click operation using the Arduino IDE, implementing more complex programs requires more robust build tools. This article describes how to build on Linux using command-line tools -- a process that is nowhere near as easy as it should be. If we can build using command-line tools, we can manage a project using Makefiles and similar techniques.

Categories: Arduino, embedded computing, C

The first step towards designing and building a custom keyboard, from the very first principles, using an Arduino-type microcontroller.

Categories: Arduino, embedded computing, C

Make an auxiliary LCD display for a computer that displays data sent to it over a USB connection. Ready-made devices of this sort are widely available, but it's more fun to build your own.

Categories: software development, C, Linux, embedded computing, Arduino

The official Raspberry Pi 7-inch touchscreen is a useful and well-designed piece of equipment but, if you're using it in a custom (hardware and/or software) build, you'll notice a lack of any relevant technical information. This article tries to supply some of that information.

Categories: Raspberry Pi, electronics, embedded computing

The Raspberry Pi is widely used as part of a more complex electronic project or construction. There's a misconception that such a construction can be powered from the same cheap, nasty USB charger that is suitable to power a Pi on its own. Attempting to do this often leads to undervoltage situations. This article explains why, and what constructors can do about it.

Categories: Raspberry Pi, electronics, embedded computing

There are relatively few good reasons for writing C code without using a standard C library. However, doing so provides valuable insights into how compilers and operating systems work, and is worth doing if only for its educational value.

Categories: software development, C, embedded computing