my recent reads..

Atomic Accidents: A History of Nuclear Meltdowns and Disasters; From the Ozark Mountains to Fukushima
Power Sources and Supplies: World Class Designs
Red Storm Rising
Locked On
Analog Circuits Cookbook
The Teeth Of The Tiger
Sharpe's Gold
Without Remorse
Practical Oscillator Handbook
Red Rabbit

Friday, May 20, 2016

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.


Wednesday, May 18, 2016

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.

Monday, May 02, 2016

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 
ShiFu is waiting to explain all of your problems...

And then ask it questions. Pick a language!
# Ruby client
$ ./explain.rb "Your phone is crashing because of REASON" 
Your phone is crashing because of the 
PCB not being manufactured to specification

# C# client
$ mono bin/Release/explain.exe "Your phone is crashing because of REASON"
Your phone is probably crashing because of stray harmonics

# C++ client
$ ./explain "Your phone is crashing because of REASON"
Your phone is crashing because of impedance in the coil

# node.js client
$ node ./explain.js "Your phone is crashing because of REASON"
Your phone is crashing because of a lack of shielding against 
alpha radiation (cosmic rays) in antenna

# Python client
$ python explain.py "Your phone is crashing because of REASON"
Your phone is crashing because of residual capacitance 
caused by the USB connector

All my notes and code are available in the LittleCodingKata GitHub repository.

Saturday, April 16, 2016

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 a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.

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 to be replacing batteries on a regular basis.

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

Here's the start of the "ding.." on a 'scope..

Tuesday, April 05, 2016

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



Monday, April 04, 2016

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.


Sunday, April 03, 2016

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 that turn on when facing a south magnetic polarity

The chip is rated for continuous output current of 25mA, so that is sufficient to drive an LED (as demonstrated here). For other switching applications, the output can be used to switch a transistor or pull a microcontroller output low.

Testing with some neodymium magnets, I get a strong full-on when the south pole of the magnets are within 23mm directly to the front of the chip. The output remains on until I pull back to over 40mm.

A common use for Hall-effect sensors is to detect and measure rotation. A good demonstration of this is to sequence a PoV display as demonstrated in Great Scott's latest video - HACKED!: Old Fan becomes a POV Display

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

Tuesday, March 22, 2016

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:
  • a non-inverting amplifier with a gain of ~3 provides the feedback required to sustain the oscillator
  • one unit buffers a half-supply voltage to provide a "virtual ground" for the non-inverting amplifier
  • a third unit buffers the output signal to avoid load interference with the oscillator
The LM324 doesn't have great upper and lower limits, and clipping is severe in the basic circuit. This is solved with diode stabilisation.

The result is a pretty decent sine wave at ~1.574kHz, very close to the theoretical resonant frequency of 1.592kHz.

Sunday, March 20, 2016

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 the ShiftDrive project). While a latched shift register provides random addressing and clean transitions to any digit, it requires the 7-segment display outputs to be decoded externally (like in code). On the other hand, the CD4026 takes care of the decoding, and external circuits just need to send a counter pulse.

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

Thursday, March 10, 2016

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 on a hacked up copper board with islands. Using the LC circuit resonant frequency formula, it's possible to work backwards from known frequency and capacitance to determine the inductance (wolframalpha is great for this).

So now I hope to get back into some RF without the nagging doubt of not really knowing what my coils are doing!

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

Here's a beautiful trace of a (nominally) 10µH choke with a 150pF capacitor. I measure the frequency at 4.26MHz, therefore an actual inductance of 9.3µH .. pretty close!


Even with a super-bodgy 4.5 turn coil whipped up on the spot and put in parallel with a 30pF capacitor, I'm still getting a decent oscillation at 34.09MHz for a calculated inductance of 0.73µH


And here's the board delivering the results:

Tuesday, March 08, 2016

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

Thursday, March 03, 2016

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 packaged 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 Chinese University. Reportedly "... soldering was troublesome, with lots of changes and no solid basic skills, so burned out the first board" ;-) But it seems persistence paid off, and ended up commercialising the kit and starting electronics business and taobao store where you can find this kit and many others.

As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub, including my annotation of the source code and schematic for the shake stick.


Monday, February 29, 2016

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 expression of the hope and aspirations of a whole bunch of people working together.

In other words, it is the ultimate maker project! Personally, I think it will be a sad day when someone declares it actually "finished".

Now at the extreme other end of the maker-scale is this neat little paper nano Sagrada Familia kit that I picked up in my travels.

I've "electrified" it to some extent with some LowVoltageGlowingLEDs that animate the background, just running off a 1.5V supply. Although I think I could have slowed down the LEDs even further.

A nice effect I think..



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

Sunday, February 28, 2016

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 repo on GitHub.



Here's a glimpse of the "modified oscillation". CH2 (red) is the LED cathode/transistor collector - as it rises and falls the LED slowly switches off then back on.


For protoboard-based builds I tend to layout the schematic with PAD tools (Pencil-Aided Design) ...