The easy or hard way to build a PWM dimmer


From what you would gather from Hackaday’s immense library of builds and projects over several years, the only way to do PWM is with a microcontroller, some code, a full-blown IDE, or even a real-time operating system. To some readers, we’re sure, this comes naturally and with an awesome toolchain it can be as easy as screwing in a light bulb. There is, of course, an easier way.

[Jestin] needed to vary the current on a small 12 Volt load. Instead of digging out an in system programmer, he turned to the classic 555 chip. With a single pot, it’s easy to vary the duty cycle of the 555 and connect that to a MOSFET. Put a load in there, and you have a very easy circuit that’s a fully functioning PWM dimmer.

If all you have are a few scraps in your part drawers, this is a very, very easy way to set up a dimmer switch. We’re also loving [Jestin]‘s improv aluminum tube enclosure, as seen in the video below.

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Hacking McDonald’s Minion toy to be an electric slidewhistle


This is a look at the brain surgery which [Tim] performed on a Happy Meal Toy. The McDonald’s package meal perk comes with one of several different Despicable Me 2 characters. But [Tim] wasn’t a fan of this one since you had to blow in it to make noise. He grabbed a 555 timer and added his own circuit to the toy which turns it up to 11 (seriously, turn your volume down before playing the video).

Disassembly includes removing a screw which needs a 3-sided screwdriver (protip: use a bench grinder and a cheap screw driver to make your own). There’s also some prying to get into the skull and then its time to work on the slide whistle. The blue tube is a regular slide whistle which you blow into from the back and pull on the red goo to change the pitch. [Tim] added a photoresistor to the mouthpiece and an LED on the slide. Moving the light source changes the intensity which is one of the adjustments to make 555 circuit howl.

We love the Happy Meal toy hacks because they seem so visceral. A couple years ago it was parts harvesting from Avatar toys. which in turn inspired a tripwire hack with a Penguin toy.

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A 555 player piano


From simple buzzers to an Atari Punk Console, the simple 555 timer chip is the foundation of a whole lot of interesting lo-fi synth projects perfect for beginners. [Steven] put together a great tutorial for using the 555 timer in a rudimentary synth, and even went so far as to build a simple electronic player piano able to play a song from a sheet of paper with punched holes.

The basic 555 oscillator circuit is very simple – just a few caps and resistors and powered by a few batteries. [Steven] built the simplest 555 circuit, but used a line of graphite drawn on a piece of paper for the resistor controlling the frequency. It’s basically a drawdio built on a breadboard, and easy enough to build for even the most neophyte electronic tinkerer.

Going one step further, [Stephen] drew a long thick line of pencil graphite on a piece of paper and mounted eleven wire loops attached to the circuit over his improvised resistor. After cutting a few holes in a piece of paper, he was able to create a simple player piano with his 555 synth. It worked well enough to play Greensleeves, and is the perfect project for the budding electronics hacker.

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555-timer charges lead acid batteries


[Kenneth Finnegan] took the focus of a great design and redirected it to solve his own problem. What results is this lead acid battery charger based on the 555 timer. It’s not a top-of-the-line, all the bells and whistles type of charger. But it gets the job done with a readily available IC and no need to code for a microcontroller.

The original idea came from a solar battery charger entered in the 555 timer contest. The main difference in application between that and [Kenneth's] application is the source. A solar array or wind turbine is limited on how much juice it can produce. But mains power can push a shocking (har-har) amount of current if you’re not paying attention. Herein lies the alterations to the circuit design. To control this he’s using a Laptop power supply as an intermediary and only implementing the constant current portion of the tradition 3-stage lead acid charging profile (those stages are explained in his write up).

He did a talk on the charger at his local radio club. You can see the 90-minute video after the break.

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Programming a 555 chip


[Phillip] needed a way to trigger an input every 8 hours or so. This is a snap with a microcontroller with a proper timer, but he recently heard about a very cool programmable timer chip that’s also a 555. Of course CSS555 timer chip has an obscure programming interface, but that isn’t a problem when you can program it yourself with a parallel port.

The CSS555 timer chip (PDF…) is a strange little beast. It’s pin compatible with everyone’s favorite timer IC, but also has a programming mode that allows the output to trigger on every 1 cycle, every 10 cycles, and so on up to one output every million cycles. Basically, it’s a 555 with a huge programmable capacitor that only costs two bucks.

After building a programming circuit from a 74125 hex buffer chip, [Philip] connected his programmer to the parallel port of an ancient PC. For a little retrocomputing cred, he wrote a small app in Forth that pushes commands from the parallel port to the CSS555 chip, greatly increasing the time delay of the chip’s stock configuration.

It’s a neat build, and an awesome introduction to a really cool timer chip. Of course this could be easily replicated with a $2 microcontroller, but that wouldn’t give [Philip] the satisfaction of using a 555.

Digital IR Theremin

Digital IR Theremin

This Digital IR Theremin creates tones based on the distance of an object from its IR sensor. There’s no microcontroller here, since the project is part of an Introduction to Digital Electronics course. Instead, it uses a handful of comparators, transistors, AND gates, and a 555 timer to make noise.

The comparators are connected to create window comparators. This configuration will output a digital 1 if the input is between two reference voltages, and 0 if it is not. Using this, the analog output of the IR range sensor can be converted to digital values.

The 555 timer takes care of creating the output waveform. A specific resistor is switched in to the timer’s RC circuit depending on which window comparator is active. This allows for a different tone to be played depending on the distance from the IR sensor.

The result is a square wave, which has a frequency dependant on how close an object is to the IR sensor. By selecting the right resistances for each distance, the theremin can be tuned to play a specific scale.

This is a neat project for people looking to learn digital electronics, and the write up does a great job of explaining the theory. After the break, check out a video of the theremin generating some tones.

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Pull-string most useless machine

The mechanical simplicity of this pull-string controlled most useless machine is delightful. You can see the metal gripper which is reaching up to tug on a light-fixture-style pull chain. This is how it turns itself off after you’ve pulled the string to power it up.

The device is [Alex555's] entry in the 7400 Logic competition. We do hope that he ends up posting a schematic because we’d love to see the gritty details of how it works. After the break you can watch two doors open, allowing the arm to raise up and the gripper to grab the chain. This takes just four servo motors, which are controlled by the signal from a 555 timer and some accompanying hardware.

Apparently the chain is a fake, as the servos didn’t provide enough force to actuate that type of switch. It’s not a surprise as those pull chains do require quite a tug. An optical sensor was used to trigger the movement when your hand reaches for the chain.

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