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.

Hackaday Prize Semifinalist: A Device For Autism and Pomodoros

[jens.andree] found that many people on the autism spectrum have problems perceiving time. This makes the simplest tasks at home or at school harder. To help solve this problem, he’s created the Timstock Slim for this year’s Hackaday Prize. It’s a timer with four buttons to count down 5, 10, 15, or 20 minutes, with a neat LED bar graph showing the remaining time.

The Timstock Slim is an extremely simple device – it’s just an ATTiny84, a few shift registers, some LEDs, resistors, buttons, and a coin cell battery clip. It also does exactly what it says on the tin; it counts out a few minutes at a time, while providing visual feedback in the form of a bunch of LEDs.

Interestingly, this device may be useful to more than just those with autism; the pomodoro technique of time management uses a similar device – a kitchen timer – to keep its adherents on track. With no modifications at all, [jens’] Timstock could be used for a slightly modified pomodoro technique, geared towards 5, 10, 15, or 20 minute increments.

The 2015 Hackaday Prize is sponsored by:

Cute Countdown Timer Reminds you of Impending Doom

As things get busy, whether it be an upcoming product launch, a pregnancy, or even the release of your favorite game (or movie!) sometimes it’s nice to have a little countdown timer. Not an app on your phone, but a tangible, physical timer to set on your desk. Which is why SevenSeg is such a cute idea.

[Mohit] wanted to design something that was simple, but aesthetically pleasing — he’d seen free-form electronic projects before and wanted to give it a shot. What he came up with is pretty elegant! A seven segment display is connected via 1/32″ brass rods to the controller, a Particle Photon — which is kind of like a Teensy with WiFi for the internet of things. After putting a few resistors in line with the display, and a bit of frustrating bending of wire later, and SevenSeg was complete.

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Nice Looking Countdown Timer for the Home Game Show Enthusiast

Every couple of weeks, [Roo’s] place of employment, TMW Unlimited, has a contest. This contest takes place in the form of a game show and the contestants have 30 seconds to pitch their current project to the group. A panel of judges vote on the best pitches. Winners receive cupcakes and drinks. Originally, stopwatches were used to keep track of the elapsed time, however, a stopwatch is not very game showy. [Roo] set out to make a countdown timer to add some authenticity to the bi-weekly event.

The main enclosure is a plastic fence post. Fifteen holes and 15 large LEDs are covered up by large plastic translucent spheres. End caps were designed and 3D printed to not only make the rig look good but also to serve as a speaker mount. Inside resides an Arduino that does the counting and turns off the row of lights, one every 2 seconds, as the countdown continues. A speaker not only ticks and tocks its way down with the lights, it also buzzes when time is up. Starting and resetting the timer is as easy as pushing a single button mounted on the case.

If you’ve already built a game show timer, you may want to check out this DIY game buzzer system!

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