An “ill” logical PWM control


[James] recently finished up a gigantic seven segment display for Nottingham Hackerspace, and although it looks great, the display isn’t the interesting part. The PWM dimmer control implemented in logic is the true head-turner. That’s right: this is done without a programmable controller.

Unsatisfied with the lack of difficulty he faced when slapping together the rest of the electronics, [James] was determined to complicate the auto-dimmer by foregoing all sensible routes. He started by building an 8-bit timer made from a 555 timer fed into a 12-bit 4040 counter. He then used an 8-bit ADC IC to read a photoresistor. The outputs from both the ADC and from the scratch-built 8-bit timer plug into an 8-bit comparator; If the values match, the comparator outputs LOW for a single clock period.

Though this set the groundwork for PWM control, [James] had to add a couple of additional logic gates into the mix to nail everything down. You can find a diagram and the details behind flip-flopping out a duty cycle on his project blog. Clever builds like this one are a rarity when a few lines of code and a microcontroller can give you numerous shortcuts. [James] doesn’t recommend that you over-engineer your PWM controller, but we’re glad he did.  Meanwhile, Moore’s Law marches on; check out what people are doing with Low-Energy Bluetooth these days.

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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Light programming for a clock


So at first glance we were thinking there wasn’t much special about this clock. It’s based on an Arduino and displays the time using a character LCD screen. But then we realized that there’s no battery-backed RTC and no buttons. How the heck do you set the time on this thing? [Mossblaser] is using a light programmer to set the time using a computer screen.

We’ve tried nearly the same data transfer technique before, using a white and black flashing computer screen to push Manchester encoding to a light dependent resistor. We were met with limited success, but you can see that [Mossblaser’s] rig is much more reliable and we think there’s a few reasons behind this. First, he’s only sending five bits per seconds, a very slow speed when it comes to digital transmissions. This helps to make up for slow LCD screen refresh. Also, the LDR is surrounded by material on the back of the case that will help to block out ambient light. And finally, he’s using a smaller part of the screen instead of flashing the whole thing. This may result in more accurate timing. You’ve got to admit, this is pretty slick!

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Sun-powered Stirling engine with automatic tracking

Check out this solar-powered Stirling engine (translated). The build is part of a high school class and they packed in some really nice features. The first is the parabolic mirror which focuses the sun’s rays on the chamber of the engine. The heat is what makes it go, and the video after the breaks shows it doing just that.

But the concept behind the mirror makes for an interesting challenge. The light energy is focused at a narrow point. When the sun moves in the sky that point will no longer be at an efficient position to power the engine. This issue is solved by a pair of stepper motors which can reposition the dish. It’s done automatically by an Arduino Uno which makes readings from four LDR (photoresistors) in that cardboard tube mounted at the top of the dish. If the light intensity is the same for all four, then the tube is pointed at the sun. If not, the motors are tweaked to get the best angle possible.

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Preheat alarm added to a basic kitchen oven

[Justin] didn’t want to keep checking if the ‘oven heating’ indicator light had gone off before popping his unbaked edibles into the oven. Many models offer a buzzer to let you know when the chosen temp is reached, but for folks who own a basic oven model there’s just a light that tells when the heating element is getting juice. Not to worry, he plied his circuit design skills and built a buzzer to alert him when the oven’s ready.

It only took a few components to accomplish the task. [Justin] uses a pair of NPN transistors triggered by a photoresistor. One transistor is responsible for switching on the buzzer, the other transistor is driven by the photoresistor and controls the base of its companion transistor (see the schematic for a better understanding).

He designed and etched a small PCB to host all the parts. As you can see above, it mounts over the indicator light and is powered by a 9V battery. There’s an on/off switch to the right so the buzzer doesn’t keep triggering while cooking, and a potentiometer allows him to fine-tune the photoresistor sensitivity.

Microcontroller comm with a computer monitor

Prolific Hack a Day author [Mike S] has been playing in his lab again and he’s come up with a neat way to talk to microcontrollers with an LCD monitor. The basic idea behind [Mike]’s work isn’t much different from the weird and/or cool Timex Datalink watch from the 1990s.

Despite the fancy dev board, the hardware is very simple – a photoresistor is pointed at a computer monitor and reads bits using Manchester encoding. The computer flashes a series of black and white screens thanks to a simple Javascript/HTML page, and data is (mostly) transmitted to the micro. [Mike] says he has about a failed message about 60% of the time, and he’s not quite sure where the problem is. He’s looking into another kind of Manchester encoding that uses samples instead of edges, so we hope everything works out for him.

This build is very similar – and was inspired by – an earlier post about microcontroller communication with flashing lights. Still, [Mike]’s build reminds us of the strangely futuristic Ironman watch we had in ’97. Check out [Mike]’s demo of his computer/micro comm link after the break and his code on github.

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Automatic flashlight tag damage sensor

You’re out at night and playing a boisterous game of flashlight tag. But how can you tell if you’ve been mortally wounded by your opponents light beam? [Kenyer] solved this problem by building a flashlight tag damage sensor which is worn by each participant. It adds a bit of the high-tech equipment used with laser tag while keeping a low-tech price tag.

The sensor relies on a light dependent resistor to register hits when a flashlight beam passes through the round window. It will only register one hit in a three-second time period. At the end of the game, the total number of hits recorded can be flashed back using an on-board LED to see who is the victor. You can see a demo of this functionality in the clip after the break.

[Kenyer] started with a breadboard prototype using an Arduino as the driver. Obviously the cost of an Arduino for every player is a bit ridiculous. He scaled down the project, running the Arduino code on an ATtiny microcontroller. Continue reading “Automatic flashlight tag damage sensor”