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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An Introduction to Clock Dividers and Psychological Warfare

A while ago, [nsayer] was inspired by a Hackaday post to build one of the most insidious means of psychological warfare. I speak, of course, of the [Lord Vetinari] clock, a clock that ticks at random intervals, but still keeps accurate time. His build, the Crazy Clock, is a small controller board for off-the-shelf clock movements that adds the [Vetinari] feature to any clock by soldering only a few wires.

The Crazy Clock is a pretty simple device consisting of only a 32.768 kHz crystal, a microcontroller, and a few transistors to pulse the movement of a clock mechanism. While psyops is great, it recently occurred to [nsayer] that this device could be used for other build.

Since the output of the Crazy Clock doesn’t necessarily have to be connected to a clock movement, [nsayer] decided to connect a LED, generating a 60Hz flashing light for a phonograph strobe. This is easy with timer prescalers and clock dividers; the original 32.768 kHz signal is divided by 8 to produce a clock that ticks every 4.096 kHz.  Divide that again by 120, and you get 34 2/15. Yes, this is all stuff you learned in fourth grade, and if you’re smarter than a third grader you can eventually whittle a 32.768 kHz clock down to a nice, round, binary number – exactly what you need for computing time.

[nsayer] posted a 240 fps (vertical) video of his Crazy Clock blinking at 60 Hz. You can see that below.

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AVR Hardware Timer Tricked Into One-Shot

[Josh] has written up two posts that those of you who use AVRs might find handy. The first post documents a C library that implements a jitter-free one-shot timer. The second post explains how it works. We think it’s such a good idea that we’re going to spoil it for you, but go ahead and read his links and check out his code.

A one-shot is a pulse generator that runs once and only once. You trigger it, it produces the desired pulse, and that’s all she wrote. Why is this handy? Many external ICs that you’ll interface with have minimum durations for signal pulses that must be respected. You could program the AVR to toggle a pin high and then sit around and wait until it’s time to toggle the pin low again, but this wastes valuable CPU time, isn’t going to be very precise, and is susceptible to timing discrepancies if interrupt routines fire in the mean time.

You’d think that you could use the hardware timers for this, but it’s not straightforward. Normally, the timers are free-running; the counter that’s keeping track of time rolls over the top and starts over again. But we just want one pulse.

[Josh]’s very clever idea abuses the timer/counter’s TOP and MATCH values in “Fast PWM” mode. Essentially you trick the counter into never matching by setting TOP below MATCH. This means that the counter spins in its loop between zero and TOP forever, doing nothing.

To break it out of its loop and enable the one-shot, you manually set the counter to a value above TOP and let it go. As it counts up, it’ll eventually hit MATCH, turn on your pin, and then keep counting. When it rolls over the top (255 + 1 = 0 for the 8-bit AVRs), your pin will be correctly turned off again and then the counter re-enters its loop. The one-shot won’t fire until you manually set the counter higher than TOP again.

So there you have it, a one-shot depending only on the hardware timer/counter module and thus immune to jitter and consuming no CPU time at all. Our hats off to you, [Josh]. Clever hack.

A Kitchen Timer Fit for MacGyver

Here’s a project that you don’t want to bring into an airport, ship through the mail, or probably even remove from your home. [ProjectGeek] has built himself a simple kitchen timer masquerading as a bomb. The build is actually pretty simple, but the end result is something that would look at home in a Hollywood action flick.

The timer circuit is built from four simple components. An 8051 microcontroller board is used as the primary controller and timer. The code is available on GitHub. This board is attached to a another board containing four momentary push buttons. These are used to program the timer and to stop the buzzing. Another board containing four 7-segment displays is used to show the remaining time on the timer. A simple piezo buzzer is used to actually alert you when the timer has run out. All of these components are connected with colorful jumper wires.

The physical part of this build is made from easily available components. Old newspapers are rolled up to form the “explosive” sticks. These are then covered in plain brown paper ordinarily used to cover text books. The rolls are bundled together and fixed with electrical tape. The electronics can then be attached to the base with some hot glue or double-sided tape.