stm32

215 Articles

The STM32 Makes For A Cheap DIY USB Soundcard

May 24, 2022 by 14 Comments

Soundcards used to be giant long 8-bit ISA things that would take up a huge amount of real estate inside a desktop computer. These days, for most of us, they’re baked into the motherboard and we barely give them a second thought. [Samsonov Dima] decided to whip up a cheap little sound card of their own, however, built around the STM32.

The soundcard is based specifically on the STM32F401. readily available on the “Green Pill” devboards. A digital-to-analog converter is implemented on the board based on two PWM timers providing high-quality output. There’s also a simulated software sigma delta ADC implemented between the audio streaming in via USB and the actual PWM output, with some fancy tricks used to improve the sound output. [Samsonov] even found time to add a display with twin VU meters that shows the audio pumping through the left and right channels.

Without test gear on hand, we can’t readily quantify the performance of the sound card. However, as per the Youtube videos posted, it appears more than capable of recreating music with good fidelity and plenty of fine detail.

If you need a cheap, simple USB sound card that you can hack away on, this might be the one for you. If you need something more suitable for a vintage PC, however, consider this instead. Video after the break.

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Gaming Mouse Becomes Digital Camera

May 16, 2022 by 15 Comments

Ever since the world decided to transition from mechanical ball mice to optical mice, we have been blessed with computer pointing devices that don’t need regular cleaning and have much better performance than their ancestors. They do this by using what is essentially a tiny digital camera to monitor changes in motion. As we’ve seen before, it is possible to convert this mechanism into an actual camera, but until now we haven’t seen something like this on a high-performance mouse designed for FPS gaming.

For this project [Ankit] is disassembling the Logitech G402, a popular gaming mouse with up to 4000 dpi. Normally this is processed internally in the mouse to translate movement into cursor motion, but this mouse conveniently has a familiar STM32 processor with an SPI interface already broken out on the PCB that could be quickly connected to in order to gather image data. [Ankit] created a custom USB vendor-specific endpoint and wrote a Linux kernel module to parse the data into a custom GUI program that can display the image captured by the mouse sensor on-screen.

It’s probably best to not attempt this project if you plan to re-use the mouse, as the custom firmware appears to render the mouse useless as an actual mouse. But as a proof-of-concept project this high-performance mouse does work fairly well as a camera, albeit with a very low resolution by modern digital camera standards. It is much improved on older mouse-camera builds we’ve seen, though, thanks to the high performance sensors in gaming mice.

Bare-Metal STM32: Using The I2C Bus In Master-Transceiver Mode

May 11, 2022 by 34 Comments

As one of the most popular buses today for on- and inter-board communication within systems, there’s a good chance you’ll end up using it with an embedded system. I2C offers a variety of speeds while requiring only two wires (clock and data), which makes it significantly easier to handle than alternatives, such as SPI. Within the STM32 family of MCUs, you will find at least one I2C peripheral on each device.

As a shared, half-duplex medium, I2C uses a rather straightforward call-and-response design, where one device controls the clock, and other devices simply wait and listen until their fixed address is sent on the I2C bus. While configuring an STM32 I2C peripheral entails a few steps, it is quite painless to use afterwards, as we will see in this article. Continue reading “Bare-Metal STM32: Using The I2C Bus In Master-Transceiver Mode” →

A modern Tamagotchi PCB design and built-up prototype

Classic Tamagotchi Is Reincarnated In Modern Hardware

May 8, 2022 by 25 Comments

If you thought that Tamagotchis were a late ’90s fad that has faded from most people’s memory by now, you’d be wrong: the franchise is still alive and well today, with new models being released regularly. But even the original model from 1996, known as Tamagotchi P1, is being kept alive by a small group of enthusiasts. When ROM dumps of the original hardware began floating around the internet a couple of years ago, even those without the real thing could run these virtual pets in an emulator.

But the whole idea of the Tamagotchi hardware was that it was portable enough to carry around anywhere. If you’re among those who missed that part of the Tamagotchi experience, you’ll be pleased to know that [JC] designed OpenTama: a portable hardware platform that runs an emulated version of the original Tamagotchi P1 software. It’s about as close as it gets to those first-generation virtual pets, but with several additions that make your life easier.

The software platform is [JC]’s TamaLib which we featured last year; in effect it’s an open-source emulator that allows the Tamagotchi ROM to run on a variety of modern hardware platforms. It also contains several additional options like the ability to save and restore your progress or to select customized ROMs. The OpenTama hardware, meanwhile, is a proper 21st-century reimplementation of the original: a small, egg-sized PCB sporting an STM32 microcontroller driving an LCD or OLED display, powered by a 100 mAh battery that can be recharged through a USB-C port.

OpenTama is not limited to the TamaLib software, either: as an open-source general-purpose platform, it can also be used as a learning tool for embedded programming, so if you’ve always wanted to program your own virtual pet, or are simply looking to build a fancy egg timer, OpenTama’s GitHub page is the way to go. We’ve seen quite a few neat Tamagotchi-like projects recently: this 3D-printed one comes with a nice retro LCD screen, while this one’s giant size ensures you don’t forget to feed it.

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Linux Fu: The Infinite Serial Port

May 3, 2022 by 23 Comments

Ok, the title is a bit misleading. Like most things in life, it really isn’t infinite. But I’m going to show you how you can use a very interesting Linux feature to turn one serial port from a microcontroller into a bunch of virtual ports. In theory, you could create over 200 ports, but the reality is you will probably want to stick with fewer.

The feature in question is what’s known as pseudoterminal or sometimes a pty or pts. These special files were made to feed data to programs that expect to accept data from a terminal. The files provide two faces. To the client, it looks like any other terminal device. To the creator, though, it is just another file. What you write to that file goes to the fake terminal and you can read anything that is sent from the program connected to the terminal. You use these all the time, probably, without realizing it since running a shell under X Windows, for example, doesn’t attach to a real terminal, after all.

You could, of course, do the same trick with a composite USB device, assuming you have one. Also assuming you can find a working driver and get it working. However, many microcontrollers have a serial port — even one with a USB converter built-in — but fewer have full-blown USB hardware. Even the ones that do are often at odds with strange drivers on the PC side. Serial ports work and work well even on the simplest microcontrollers.

The Plan

The plan is simple enough. A Linux program listens to a real serial port and watches for special character sequences in the data stream. Those sequences will allow you to switch data so that the data stream will go to a particular terminal. Data coming back from the terminals will go to the real serial port after sending a sequence that identifies its source.

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Arming With An OS

April 13, 2022 by 28 Comments

We see tons of projects with the infamous “Blue Pill” STM32 boards. They are cheap and plentiful and have a lot of great features, or at least they were before the chip shortage. I recently picked up a “Black Pill”, which is very similar but has an even more powerful processor. For a few bucks, you get an ARM CPU that can run at 100 MHz (but with USB, probably 96 MHz). There’s 512 kB of flash and 128 kB of RAM. There’s a USB type C port, and even a button and an LED onboard. The thing fits on a breadboard and you can program it with a cheap STLink dongle which costs about $10.

The Black Pill module on a breadboard.

Of course, you then have to consider the software. The STM32Cube stuff is a lot to set up and learn but it does let you do just about anything you can imagine. Then there is the STM32Duino plug-in that lets you use it as a beefy Arduino. That works and is easy enough to set up. However, there’s also Mbed. The only problem is that Mbed doesn’t work right out of the box. Turns out, though, it isn’t that hard to set up. I’ll show you how easy it is to get things going and, next time, I’ll show you a practical example of a USB peripheral that uses the mBed RTOS features.

First Steps

Obviously, you are going to need a Black Pill. There are at least two choices but for as cheap as they are there is little reason not to get the STM32F411 version that has more memory. The DIP form factor will fit in whatever breadboard you happen to have and a USB C cable will power the board so unless you are driving a lot of external circuitry, you probably don’t need an external supply.

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The BluePill board used for this hack, wired to the DYMO RFID reader, after all the wires for this hack have been soldered onto the BluePill board.

#FreeDMO Gets Rid Of DYMO Label Printer DRM

March 30, 2022 by 49 Comments

DYMO 550 series printer marketing blurb says “The DYMO® LabelWriter® 550 Turbo label printer comes with unique Automatic Label Recognition™”, which, once translated from marketing-ese, means “this printer has DRM in its goshdarn thermal stickers”. Yes, DRM in the stickers that you typically buy in generic rolls. [FREEPDK] didn’t like that, either, and documents a #FreeDMO device to rid us of yet another consumer freedom limitation, the true hacker way.

The generic BluePill board and two resistors are all you need, and a few extra cables make the install clean and reversible – you could definitely solder to the DYMO printer’s PCBs if you needed, too. Essentially, you intercept the RFID reader connections, where the BluePill acts as an I2C peripheral and a controller at the same time, forwarding the data from an RFID reader and modifying it – but it can also absolutely emulate a predetermined label and skip the reader altogether. If you can benefit from this project’s discoveries, you should also take a bit of your time and, with help of your Android NFC-enabled phone, share your cartridge data in a separate repository to make thwarting future DRM improvements easier for all of us. Continue reading “#FreeDMO Gets Rid Of DYMO Label Printer DRM” →