Your Puzzle’s Done When The Electronics Says So

We can race against the clock when assembling jigsaw puzzles online but what about competing against each other in the real world? [HomeMadeGarbage] came up with the simplest of solutions with his jigsaw puzzle timer that stops only when the puzzle’s completely assembled.

Copper strip on back of puzzle
Copper strip on back of puzzle

His simple solution was to attach copper foil tape to the back of the pieces, with overlap. He did this in a serpentine pattern to ensure that all pieces had a strip of the tape. The puzzle he used comes with a special container to assemble it in. At two corners of that container, he put two more pieces of copper foil, to which he soldered wires. Those two act as a switch. Only when the puzzle is completed will those two pieces be connected through the serpentine strip on the back of the puzzle.

Next, he needed a timer. The two wires from the puzzle container go to an Arduino UNO which uses an ILI9325 touch panel TFT display for both the start, stop, and reset buttons, and to show the time elapsed. Press the touch screen when it says START and begin assembling the puzzle. When the last piece is inserted, the serpentine strip of copper tape completes the circuit and only then does the Arduino program stop the timer. As you can see from the video below, the result makes doing the puzzle lots of fun.

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Building an OBD Speed Pulse: Behold the ICE

I am a crappy software coder when it comes down to it. I didn’t pay attention when everything went object oriented and my roots were always assembly language and Real Time Operating Systems (RTOS) anyways.

So it only natural that I would reach for a true In-Circuit-Emulator (ICE) to finish of my little OBDII bus to speed pulse generator widget. ICE is a hardware device used to debug embedded systems. It communicates with the microcontroller on your board, allowing you to view what is going on by pausing execution and inspecting or changing values in the hardware registers. If you want to be great at embedded development you need to be great at using in-circuit emulation.

Not only do I get to watch my mistakes in near real time, I get to make a video about it.

Getting Data Out of a Vehicle

I’ve been working on a small board which will plug into my car and give direct access to speed reported on the Controller Area Network (CAN bus).

To back up a bit, my last video post was about my inane desire to make a small assembly that could plug into the OBDII port on my truck and create a series of pulses representing the speed of the vehicle for my GPS to function much more accurately. While there was a wire buried deep in the multiple bundles of wires connected to the vehicle’s Engine Control Module, I have decided for numerous reasons to create my own signal source.

At the heart of my project is the need to convert the OBDII port and the underlying CAN protocol to a simple variable representing the speed, and to then covert that value to a pulse stream where the frequency varied based on speed. The OBDII/CAN Protocol is handled by the STN1110 chip and converted to ASCII, and I am using an ATmega328 like found on a multitude of Arduino’ish boards for the ASCII to pulse conversion. I’m using hardware interrupts to control the signal output for rock-solid, jitter-free timing.

Walk through the process of using an In-Circuit Emulator in the video below, and join me after the break for a few more details on the process.

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Brake Light Blinker Does It with Three Fives

Sometimes you use a Raspberry Pi when you really could have gotten by with an Arudino. Sometimes you use an Arduino when maybe an ATtiny45 would have been better. And sometimes, like [Bill]’s motorcycle tail light project, you use exactly the right tool for the job: a 555 timer.

One of the keys of motorcycle safety is visibility. People are often looking for other cars and often “miss” seeing motorcyclists for this reason. Headlight and tail light modulators (circuits that flash your lights continuously) are popular for this reason. Bill decided to roll out his own rather than buy a pre-made tail light flasher so he grabbed a trusty 555 timer and started soldering. His circuit flashes the tail light a specific number of times and then leaves it on (as long as one of the brake levers is depressed) which will definitely help alert other drivers to his presence.

[Bill] mentions that he likes the 555 timer because it’s simple and bulletproof, which is exactly what you’d need on something that will be attached to a motorcycle a be responsible for alerting drivers before they slam into you from behind.

We’d tend to agree with this assessment of the 555; we’ve featured entire 555 circuit contests before. His project also has all of the tools you’ll need to build your own, including the files to have your own PCB made. If you’d like inspiration for ways to improve motorcycle safety in other ways, though, we can suggest a pretty good starting point as well.

Very Clever 555 Bassline Synth/Sequencer

If we had a dime for every 555-based noisemaker circuit we see… But this one’s got a twist.

[Tristan] does two things that elevate his sawtooth-wave noisemaker above the norm. First, he gets a clean sawtooth wave out of it so that it sounds about right. Then he manages to make it more or less playable. It’s a refined version of a classic hack.


The first trick is a matter of putting a constant current supply upstream of the timing capacitor. The usual 555-timer circuit just charges the capacitor up from the power rails through a resistor. This is fine if all you care about is timing. But because the current is proportional to the constantly dropping voltage difference, the voltage on the capacitor is an exponential function over time.

A simple transistor current source linearizes the waveform in no time. Raw sawtooth waves are “rich in harmonics” which is synth-geek code for “a bit grating”, but it will surely do well with a little filtering. The Javascript suggests that he’s already thinking in that direction, but we’re going to need video proof!

The second cool trick up [Tristan]’s sleeve is the light-dependent resistor (LDR) that determines the pitch. Yeah, we’ve all made those before — the light-dependent “Theremin”. But [Tristan] took the extra step and wrote up a Javascript application that makes his monitor brighter and darker, enabling him to get musical pitches out of the gizmo.

We’ve always wanted to implement LED-to-LDR control while writing the Logic Noise series, but never found a reliable way to make it work. It’s cool to see [Tristan]’s efforts. Maybe we’ll pull a 555 out of the junk box in his honor.

Nixie Timer is Easy to Read Across the Kitchen

Nixie clocks. Nixie power meters. Nixie thermometers, speedometers, and even Nixies for personal adornment. Is there anything that hasn’t been Nixie-fied? How about a Nixie kitchen timer? Beyond the Nixie tube, this is a great build. Check out the video below the break.

As so often happens with Nixie aficionados, [Kouichi Kuroi] started with tubes and searched for a project to use them on. A wonky kitchen timer provided the thinly veiled excuse for the build – after all, anyone can drop a couple of yen on a commercial replacement, right? The timer features four IN-12 tubes and a large numeric keypad up front on a laser-cut acrylic case. For those who quibble with the keypad’s aesthetics and the wisdom of a Nixie project in the kitchen environment, [Ko] points out that an IP65 keypad would have more than doubled the price of the build, and a little common sense goes a long way to keeping the high-voltage side from meeting anything wet. In addition to countdown capability, the timer can also act as a stopwatch and display the time of day, and the Nixie tubes provide great visibility compared to seven-segment LCD timers.

As for the aforementioned Nixie projects, here’s a clock, power meter, thermometer, speedometer and necklace that we’ve featured before. What’s next for Nixies? We don’t know, but we’re keen to see what you come up with.

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Tiny Tea Timer for Your Perfect Cuppa

If you’re serious about your tea, you know that the line between a perfect brew and over-steeped dreck is a fine one. Seconds can make a difference, and for the tinkering tea drinker, this might lead you to build a tiny timer with just the features it needs to achieve tea perfection.

The circuit that tea-loving [acidbourbon] came up with for his timer is simplicity itself. It’s just an ATtiny25, an  LED, two pushbutton switches and a piezo buzzer on one side of the PCB, with a coin battery on the flip side. The battery holder is an interesting design – a couple of rows of pin headers and a bit of springy metal. The user interface is as simple as the circuit – the buttons increment the time either one or ten minutes. The timer starts right away, the LED heartbeat counts down the seconds, and a distinctly British tune announces when it’s time for tea.

One possible improvement might be to have the LED flash the number of minutes remaining rather than just a single pulse heartbeat. That would be good feedback that you entered the right time in the first place. Other than that, it’s small enough to be handy, does just one job, and does it well – sounds like good design to us. Of course, if you want to complicate it a bit, you could always automate the tea steeping process.

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555 Teardown and Analysis

If you are even remotely interested in electronics, chances are the number ‘555’ is immediately recognizable. It is, after all, one of the most popular IC’s ever built, with billions of units sold to date. Designed way back in 1970 by Hans Camenzind, it is still widely available and frequently used for various applications. [Ken Shirriff] does a teardown and analysis of a 555 and gives us a look at the internal structure of this oldie.

A metal can package allowed him to just chop off the top and get access to the die, which was way safer and easier than to etch out the black epoxy of a DIP package. He starts by giving us a quick run down on how the chip works, showing us the two comparators, the output flip-flop and the capacitor discharge circuitry that make up most of the chip. He then puts the die under a metallurgical microscope, and starts identifying the various sections of the chip. Combining pictures of individual elements with cross-sectional diagrams, he identifies the construction of the transistors and resistors, the use of a current mirror to replace bulky resistors, and the differential pair that makes up the comparators.

He wraps it up by providing an interactive map of the die and the schematic, where you can click on various parts and the corresponding component is highlighted along with an explanation of what it does. There’s some interesting trivia about how a redesigned, improved version – the ZSCT1555 – couldn’t survive the popularity and success of the 555. He wraps it up with a useful list of notes and references. While de-capping blog posts are interesting on their own, [Ken] does a great job by giving us a detailed look at the internals.

Thanks [Vikas] for sending in this tip.