Fixing A Cheap UPS HAT For Your Raspberry Pi With A Tiny Daemon

An uninterruptible power supply (UPS) isn’t something solely to have hooked up to your desktop PC. Your Raspberry Pi SBC might also benefit from it. Yet the available options aren’t too great, or are too expensive. This leads folk including [Joachim Baumann] to modify cheerfully cheap Chinese UPS HAT boards such as the Geekworm UPS HAT to fix its myriad of issues and missing features.

Inspired by a number of other hacks on this board which fixed things like needing to push a button on the UPS to boot the Raspberry Pi, [Joachim] set out to make a similar ATtiny-based solution that would address all issues, above all the fact that this Geekworm UPS does not detect when the connected SBC has turned off and will happily run the lithium battery pack dry. Finding a blog post by Simon who had reverse-engineered the board previously was immensely helpful. Continue reading “Fixing A Cheap UPS HAT For Your Raspberry Pi With A Tiny Daemon”

Tiny Two-Digit Thermometer Has Long Battery Life

Like most of his work, this tiny two-digit thermometer shows that [David Johnson-Davies] has a knack for projects that make efficient use of hardware. No pin is left unused between the DS18B20 temperature sensor, the surface mount seven-segment LED displays, and the ATtiny84 driving it all. With the temperature flashing every 24 seconds and the unit spending the rest of the time in a deep sleep, a good CR2032 coin cell should power the device for nearly a year. The board itself measures only about an inch square.

You may think that a display that flashes only once every 24 seconds might be difficult to actually read in practice, and you’d be right. [David] found that it was indeed impractical to watch the display, waiting an unknown amount of time to read some briefly-flashed surprise numbers. To solve this problem, the decimal points flash shortly before the temperature appears. This countdown alerts the viewer to an incoming display, at the cost of a virtually negligible increase to the current consumption.

[David]’s project write-up explains how everything functions. He also steps through the different parts of the source code to explain how everything works, including the low power mode. The GitHub repository holds all the source files, and the board can also be ordered direct from OSH Park via their handy shared projects feature.

Low power consumption adds complexity to projects, but the payoffs can easily be worth the time spent implementing them. We covered a detailed look into low power WiFi microcontrollers that is still relevant, and projects like this weather station demonstrate practical low power design work.

DIY Button Matrix Lights Up And Speaks I2C

[David Johnson-Davies] always wanted an illuminated button matrix for projects, but cost was never very friendly. That all changed when he discovered a cheap source of illuminated pushbuttons on Aliexpress, leading to this DIY 4×4 illuminated button matrix design which communicates over I2C. The button states can be read independently of setting the light pattern, and an optional interrupt signal gets pulled low whenever there is a change detected. Not bad for one PCB plus about $10-worth in components!

The device uses every single pin on an ATtiny88, and because each button gets its own pin the keypresses can be detected with pin-change interrupts. The state reporting of buttons over I2C is unambiguous, even when multiple buttons are pressed simultaneously. A simple protocol provides all the needed functionality, and all connections are brought to the board’s edge to allow for easily tiling multiple panels.

The GitHub repository contains the code and PCB files and [David] helpfully shared the board files to OSH Park and PCBWay for easy ordering. In addition, he provides two demos (Tacoyaki and Tacoyaki+) which are games related to the classic Lights Out to show off the matrix.

ATtiny Gets A Tiny Software UART

Modern microcontroller platforms spoil us with their performance and expansive spec sheets. These days it’s not uncommon to be developing for a cheap micro that has a clock rate well in excess of 100MHz, with all manner of peripherals baked in. DACs, WiFi, you name it – it’s in there, with a bunch of libraries to boot. It wasn’t always this way, and sometimes you would even find yourself lacking hardware serial support. In these cases, the bitbanged software UART is your friend, and [MarcelMG] decided to document just how it’s done.

The amateur programmer’s first recourse may be to use delays to properly time the output data stream. This has the drawback of wasting processor cycles and doesn’t let the microcontroller do much else useful. Instead, [Marcel] discusses the proper way to do things, through the use of interrupt service routines and hardware timers.

[Marcel]’s implementation is for the ATtiny24A, though it should be easily portable to other AVR8 processors. Taking up just 2 bytes of RAM and 276 bytes of program space, it’s compact – which is key on resource-limited 8-bit devices. The code is available on Github if you fancy trying it out yourself.

It’s a technique that is more than familiar to the old hands, but useful to those new to the art. It can be particularly useful if you need to get data out of a legacy platform with limited options. As times change, it’s important to pass on the techniques of yesteryear to the new generation. Of course, if things are really tight, you can even do a half-duplex UART on a single pin.

 

Get Twelve Charlieplexed PWM Outputs From An ATtiny85

Most of us are aware that charlieplexing can drive a large number of LEDs from a relatively small number of I/O pins, but [David Johnson-Davies] demonstrates adding another dimension to that method to create individually controlled PWM outputs as well. His ATtiny85 has twelve LEDs, each with individually-set brightness levels, and uses only four of the five I/O pins on the device.

Each LED can be assigned a brightness between 0 (fully off) and 63 (fully on). The PWM is done by using one of the timers in the ATtiny85 to generate a periodic interrupt, and the ISR for the interrupt takes care of setting the necessary ratios of on and off times for each charlieplexed output. The result? Twelve flicker-free LEDs with individually addressable brightness levels, using an 8-pin microcontroller and just a few passive components on a tiny breadboard. There’s even one I/O pin left on the ATtiny85, for accepting commands or reading a sensor.

[David] really wrings a lot out of the ATtiny series of microcontrollers with his compact projects, like his Tiny Function Generator (which recently got an update.) He also demonstrated that while charlieplexing is usually used with LEDs, charlieplexing can be used with switches just as easily.

Ultra Tiny PC Plays Snake

[Steve Martin] used to do a comedy act about “Let’s get small!” You have to wonder if [Paul Klinger] is a fan of that routine, as he recently completed a very small 3D printed PC that plays snake. Ok, it isn’t really a PC and it isn’t terribly practical, but it is really well executed and would make a great desk conversation piece. You can see the thing in all its diminutive glory in the video below.

The 3D printer turned out a tiny PC case, a monitor, and a joystick. The PC contains an ATtiny1614, an RGB LED, and some fiber optic to look like case lighting. The monitor is really a little OLED screen. A 5-way switch turns into the joystick.

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Tiny Amplifier With ATtiny

Small microcontrollers can pack quite a punch. With the right code optimizations and proper use of the available limited memory, even small microcontrollers can do things they were never intended to. Even within the realm of intended use, however, there are still lots of impressive uses for these tiny cheap processors like [Lukasz]’s audio amplifier which uses one of the smallest ATtiny packages around┬áin the video embedded below.

Since the ATtiny is small, the amplifier is only capable of 8-bit resolution but thanks to internal clock settings and the fast PWM mode he can get a sampling rate of 37.5 kHz. Most commercial amplifiers shoot for 42 kHz or higher, so this is actually quite close for the limited hardware. The fact that it is a class D amplifier also helps, since it relies on switching and filtering to achieve amplification. This allows the amplifier to have a greater efficiency than an analog amplifier, with less need for heat sinks or oversized components.

All of the code that [Lukasz] used is available on the project site if you’ve ever been curious about switching amplifiers. He built this more as a curiosity in order to see what kind of quality he could get out of such a small microcontroller. It sounds pretty good to us too! If you’re more into analog amplifiers, though, we have you covered there as well.

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