LittleArduinoProjects now with fancy catalog!

I keep finding new uses for GitHub Pages - situations where in the past I would otherwise have spun up a web site on heroku or similar. But if the site can be static, and especially if you are already hosting the git repository at GitHub, Pages are perfect.

For a long time, I've maintained the LittleArduinoProjects project index as a simple table in the README. But it wasn't particularly nice or usable, so I (more...)

On "random" CI failures

I closed a bug yesterday that's been kicking around for almost a year as a sometimes fails on CI but no-one can figure out why frustration.

Sooner or later you'll hear someone suspect it must be a problem with CI. Which is ironically funny in a shoot-the-messenger kind of way!

Thankfully our "CI issue" turned into a for-real bug. In short, the code involved many classes with near 100% test coverage. It had been read (more...)

LittleArduinoProjects#204 Type K Temperature Logger

I'm working on an idea where I need to measure temperatures to around 500°C - above those typically supported with semiconductor sensors or thermistors.

This project demonstrates the basic approach using an Arduino as the "temperature logger". I'm using a K Type thermocouple that's rated up to 700°C. Since thermocouples only measure a differential temperature, I'm also using an LM35 to provide the cold-junction baseline. The temperature measurement is displayed on a 5110 LCD.

As (more...)

阿部真央 Don’t let me down

One of the best finds in the racks at Tower Records Fukuoka福岡市. It's been years since I last got to browse a record store in Japan; I'm glad they still exist, with stacks of CD players queued up to sample. And a huge relief to see the indie rock scene is just as vibrant as I remember!

LittleArduinoProjects#203 Homopolar Motor

What happens when electric fields cut across magnetic fields? A force is generated, and the homopolor motor is the classic demonstration.

As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub.


LittleArduinoProjects#202 LM3915 Audio Level Kit

The LM3915 is a useful IC for simple audio level displays. This is a cheap kit build which largely follows the reference circuits in the datasheet.

As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub.

LittleCodingKata: Hardware Excuse Generator with gRPC

gRPC is a very interesting lightweight middleware framework for language-neutral, cross-platform RPC.

When I heard about Natalie Silvanovich's Hardware Excuse Generator on Embedded.fm, I immediately recognised a better "Hello World" for testing out gRPC.

Introducing "The Explainer": my programming exercise to learn basic cross-language request/reply with gRPC.

I haven't completed the whole matrix of client-server possibilities yet, but here's a sampling...

Start up a server (e.g ruby version)
$ ./explainer.rb 
(more...)

Embedded: Specialization is for insects

embedded.fm has fast become my favourite podcast of the moment (always excepting QOTD). Great ideas shared in an inclusive and warm-fuzzy way.

Elecia's end-of-show quote always makes it worth listening right to the end. Until I heard #146's,
I'd struggled to find words to express exactly this. It's a quote from Robert A. Heinlein:

A human being should be able to change a diaper, plan an invasion, butcher a hog, conn (more...)

LittleArduinoProjects#201 Yet Another Doorbell

aka door-fart according to my better half ... 555 Timer-based oscillators are not exactly the most musical creatures.

#201 is a kit build. Ridiculously cheap on aliexpress, it even came with extra components, so a bit of a bargain impulse-buy.

The kit turned out to be a simplified version of a circuit I've built before. It lacks the power control circuit, and draws about 4mA when idle - so if you actually use it, expect (more...)

LittleArduinoProjects#200 Mini Solenoid Engine

Solenoid engines? They definitely fall into the the category of because you can.
Some people take it to a whole other level (like this V8 model).

What I have here is much more modest - a single-cylinder engine powering an impromptu-wire-art drive train. The mini-solenoid used here has a very small effective stroke - about 8mm - which necessarily constrains the gearing. I was inspired by 30GB's similar model for the layout.

As (more...)

LittleArduinoProjects#199 CD4026 Bucket-brigade LED driver

This is an extension if the ideas in #196, demonstrating how it's possible to build a "bucket-brigade" of CD4026 chips to drive an arbitrary number of 7-segment LEDs with a single data line.

It just requires the carry-out from the first CD4026 to be chained as the clock input for the second and so on.

As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub.


LittleArduinoProjects#198 Hall Effect Switch

Hall-effect sensors generally support one of three modes:
  • switch - turn on in the presence of a magnetic field of a specified polarity
  • latch - turn on in the presence of a magnetic field, and stay on until exposed to the reverse polarity
  • linear sensor - output is proportional to the magnetic field strength
The components I have for testing are marked "44E/938" and are nominally compatible with the A3144 or OH3144. These are switches (more...)

LittleArduinoProjects#197 Wien Bridge Audio Tone Generator

A Wien bridge oscillator is essentially an RC Band Pass Filter with a high Q factor at the resonant frequency, and generates a nice sine wave. I wanted a simple audio-frequency test signal generator, and a Wien Bridge turned out to be perfect for the job.

As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub.


A good old LM324 does triple duty in the circuit:

LittleArduinoProjects#196 Driving a 7-segment display with CD4026 Counter

Here's yet another way to drive a 7-segment single-digit display unit - using a CD4026.

The CD4026 is a 5-stage Johnson decade counter with decoded 7-segment display outputs and display enable. With RESET and CLOCK INHIBIT low, and DISPLAY ENABLE IN high, the 7-segment display outputs progress through the 0-9 sequence on the rising edge of the CLOCK pulse.

It's an interesting alternative to a shift register for driving a 7-segment LED (as in (more...)

LittleArduinoProjects#195 Coil Resonance and Inductor Testing

I've been trying to do some RF experiments, but instead being driven mad by hand-wound coils that never seem to behave as the standard coil inductance calculations would lead us to believe.

As always, it's w2aew to the rescue with a neat deconstruction and demo of a circuit for coil or inductor measurement.

I built the circuit out, and was easily measuring down to 10µH on a breadboard, and sub-1µH once I put the circuit (more...)

LittleArduinoProjects#194 DIY ESP8266 DevBoard

With the funding of the MicroPython on the ESP8266 campaign, my interest in the ESP8266 is rekindled!

I have an ESP-01 module lying around, but I'm a bit tired of wiring it up a breadboard again. So here is a little "devboard" I whipped up on a 4x6cm protoboard and hot-glued to a business card holder.

Now it's plug'n'play - add power and plug in a USB serial adapter and I'm good to go.

As (more...)

LittleArduinoProjects#193 PoV LED Shake Stick

This AT89S52-based "shake stick" kit pops up all over the place for a few dollars. I built it and hey, it works great!

But it's not pacakged to be easily re-programmed for other messages or graphics. So started my sleuthing.. which turned into a fascinating story.

It seems the kit was originally designed and built as a uni project by Zheng Zhong Xing 兴向荣 (aka zhengzhongxing39) studying Control Technology and Instruments/Principles and Applications at a (more...)

LittleArduinoProjects#192 Sagrada Família model with LED effects

The Basílica i Temple Expiatori de la Sagrada Família has been under construction since 1882. The magnitude of the vision driving the project - both physically and creatively - is striking, especially at first hand.

Then you see the work in progress - the cranes, scaffolding, workers scurrying around the site. But that is what I think really brings it to life. This is not a frozen, finished statement of something other-worldy. It's a vibrant (more...)

LittleArduinoProjects#191 glowing LEDs on 1.5V

So for another project I wanted some "glowing" LEDs, ideally powered from a single 1.5V AA or AAA battery. That seemed like an interesting challenge, especially when the forward voltage of the LEDs I'm using is about 2.1V.

I had a feeling I could cobble together a couple of ideas (Relaxation Joule Thief and RC Oscillator) .. and lo, it works!



As always, all notes, schematics and code are in the Little Arduino Projects (more...)

LittleArduinoProjects#137 Toroidal Joule Thief

In #129 I posted about a two-transistor boost circuit. This is an even simpler circuit - very common over around the internet and known as the archetypal "joule thief". The smallest I've seen is Eric Wasatonic's micro version.

I stuffed my circuit into a AA battery holder and it works great as a night light, powered by either a single somewhat-depleted AA or AAA battery.

As always, all notes, schematics and code are in the (more...)