It’s that time of year again where the thermometer drops, the sun sets earlier, and we try to warm our hearts with the solstice festival that is common in our own respective cultures. Of course we all need a few strings of lights, but wouldn’t it be great if we had PWM controlled dimmable lights?

When he started out on his PWM-controlled, AC-powered light box, [Waterbury] immediately realized that relays were not going to be an optimal solution. The best way out of the mess he dug himself into would be via zero crossing. After getting a transformer wired up to a transistor for the detection circuit, a short bit of code was written in the wee hours of the morning and a proof of concept was had.

With the control box complete, [Waterbury] hacked up a quick VB app and piped the output of a WinAmp visualizer into the lights via serial. The Inception demo was great, but finer-grain control was needed. After seeing a Hack a Day post on a nice equalizer chip, the seven band output on IC were converted to UART.

[Waterbury] took his seven-band AC-controlled light box to a Halloween party with his synth and the results looked awesome. You can check that out after the break, but we’re really waiting to see his Christmas decorations this year.

The folks over at Toymaker Television have put together another episode. This time they’re looking at bridge rectifiers and how they’re used in AC to DC converters.

This is a simple concept which is worth taking the time to study for those unfamiliar with it. Since Alternating Current is made up of cycles of positive and negative signals it must be converted before use in Direct Current circuits; a process called rectification. This is done using a series of 1-way gates (diodes) in a layout called a bridge rectifier. That’s the diamond shape seen in the diagram above.

This episode, which is embedded after the break, takes a good long look at the concept. One of the things we like best about the presentation is that the hosts of the show talk about actual electron flow. This is always a quagmire with those new to electronics, as schematics portray flow from positive to negative, but electron theory suggests that actual electron flow is the exact opposite.

[Todd Harrison] needed a way to run a 12 volt PC fan from mains voltage. Well, we think he really just needed something to keep him occupied on a Sunday, but that’s beside the point. He shows us how he did this in a non-traditional way by using the resistive load of an incandescent light bulb, a diode, and a capacitor to convert voltage to what he needed. You can read his article, or settle in for the thirty-five minute video after the break where he explains his circuit.

The concept here is fairly simple. The diode acts as a half-wave rectifier by preventing the negative trough of the alternating current from passing into his circuit. The positive peaks of the electricity travel through the light bulb, which knocks down the voltage to a usable level. Finally, the capacitor fills the gaps where the negative current of the AC used to be, providing direct current to the fan. It’s easy to follow but the we needed some help with the math for calculating the correct lightbulb to use to get our desired output current.

Prepare to learn. [Grenadier] has put together a collection of information about AC electricity that can safely be called a super-post. In 62 parts he covers a myriad of topics, some of them safe, many of them not so much. You may want to spend time reading through everything that he has to offer, but just in case you don’t, step one is a table of contents. In it you’ll find a listing of major points including transformers of every kind imaginable; from microwave ovens, neon signs, bug zappers, x-rays, and televisions. [Grenadier] covers the type of transformers that these items use, where to find them, and how to set up your own experiments. There’s plenty of pictures and several videos where the high-powered sparks fly. We feel like there’s enough here that we can be satisfied with vicarious AC interactions while safely in front of our monitor and far away from the heart-stopping action.

[Thanks Marcus]

[Kusnick] is into using digital camera rigs for book scanning. The problem is that keeping the batteries charged is a pain, but there’s no external AC adapter jack which would allow him to use the mains. His solution was to build his own adapter to replace the batteries.

There are some fancy book scanning setups that allow you to just flip through the pages, but it’s much simpler to build a rig that uses two cameras. [Kusnick's] setup is the latter, which means he’s found two inexpensive cameras that don’t need to be mobile. The first attempt at making an adapter featured a block of acrylic with the positive and negative contacts connected to a shielded cord which he then hooked to an external supply. The camera would come on and then turn off citing that the cameras were “for use with compatible battery only”. Turns out there’s some type of verification circuit built into the proprietary batteries. But the solution to that came quite easily; remove the circuit board from the battery and insert it in the adapter to trick the camera.

[Thanks Daniel]

This collection of touch sensor information should be of interest to anyone who liked the simple touch sensor post from Thursday. That was a resistive touch sensor and is covered in detail along with AC hum sensors that trigger based on induced current from power lines around you, and capacitive touch switches like we’ve seen in past hacks. Each different concept is discussed and clearly illustrated like the slide above. [Giorgos Lazaridis] has also put together individual posts that build and demonstrate the circuits. We’ve embedded his resistive sensor demo video after the break and linked to all three example circuits.

Resistive touch sensor video:

• Resistive touch sensor circuit
• AC hum circuit
• Capacitive touch circuit

[Thanks Giorgos and Ben]

[Ladyada] is working on a tutorial series covering power supplies. If you’ve ever built an electronic project you’ve used some type of power supply but we think that most people have no idea how you get from mains power to the DC voltages that most small projects use. So if you want to learn, get started with the first installment which covers AC/DC converters based on a transformer like the one seen above.

These transformers are inside the heavy and hot wall-wart plugs that come with many electronics. We used one along with a breadboard power supply when building the pumpkin LED matrix. They use a pair of coils to step down the voltage to a much smaller level. From there it’s a matter of rectifying the AC into DC power, which she talks about in an easy to follow discussion.

We understand this type of converter quite well but we’re a bit foggy on switch-mode AC/DC converters that don’t use a transformer. They’re much better because you don’t have to build a regulator into the target project like you do with wall-warts. Can’t wait until she gets to that part of the series!

[Jeri's] back with a series of videos that outlines the step-by-step electroluminescent wire manufacturing, making EL panels from PCBs, and assembling power supplies for EL hardware. These concepts are actually quite approachable, something we don’t expect from someone who makes their own integrated circuits at home.

The concept here is that an alternating current traveling through phosphors will excite them and produce light. You need two conductors separated by a dielectric to get the job done. For wire, [Jeri] uses one strand of enameled magnet wire and one strand of bare wire. The enamel insulates them, protecting against a short circuit.

But that’s not all, she also tests using a circuit board as an EL panel. By repurposing the ground plane as one of the conductors, and using the solder mask as the dielectric she is able to paint on a phosphor product resulting in the glowing panel.

Finally, you’ve got to get juice to the circuit and that’s where her power supply video comes into the picture. We’ve embedded all three after the break. It’s possible that this is cooler than blinking LEDs and it’s fairly inexpensive to get started. The circuitry is forgiving, as long as you don’t zap yourself with that alternating current.

EL wire manufacturing

Making EL panels from PCBs

EL power supplies

An Arduino with 40 lines of code, a temperature resistor, and servo are all that’s truly needed to save some dough with this thermostat by [Peter Hamilton]. LEDs and a potentiometer are added as well to help set and read the desired temperature. With or without said additional parts, the hack is still ridiculously simple and we’re wondering why we didn’t have a similar setup on our blisteringly cold office AC system before seeing it.

Though, we’re going a bit further with our version, plans are in the making to add timers to turn off the system for extended hours while no one is at the office. What would you add?

[Josiah] said ‘no’ to LEDs and instead used blue-phosphor neon lamps to build this binary clock. The ATmega328 inside uses three 8-bit shift registers to control the display. Each lamp needs a high-voltage NPN transistor in order to switch on the 150V necessary for proper illumination. A simple circuit was used to pull a 60 Hz clock signal out of the incoming 16VAC power. Unfortunately it was a bit too simple and didn’t provide a clean signal. [Josiah's] workaround is something of a debounce subroutine in the firmware to prevent multiple interrupts on the falling edge.

The last project we saw from [Josiah] was the Coachella Lamp. That was a show piece of antiquated technology and this is another show piece with a minimalistic style. We also liked seeing the protoboard work on the inside. That’s a pretty jam-packed circuit board and keeping everything in the right place while you build up each trace with blobs of solder is no small feat.

Reader [Tim Upthegrove] sent in a novel take on powering and monitoring AC outlets and devices called SPRIME, or Simple Powerline Remote Interactive Monitor and Enforcer. Compared to previous hacks, such as 120v switching or Quick cheap remote outlets, that only turned an outlet on or off; SPRIME allows not only control over outlets via the internet, but also power usage of devices currently plugged in.

We really liked their idea of giving power companies access to SPRIME outlets to reduce power consumption during peak hours, but sadly we don’t see it being implemented in homes any time soon. Catch a video of SPRIME after the rift.

[Thanks Chris McClanahan and Jeff Starker for the project, and deyjavont for pointing out our silly mistakes]

[Lucassiglo21] developed this logic clock without using a crystal oscillator or a resonator. Instead, he’s letting the incoming electricity keep the time for him. The supply is AC at 50 Hz so he’s using some 4017 decade dividers to reduce that down to a 1 Hz signal. From there it keeps track of the ticks just like the last digital logic clock we saw.

If you’ve used AC line frequency as the clock source in your project we’d like to hear about it. Send us a tip and make sure your writeup includes a schematic. We’re especially interested to see if anyone has a good way of using this method with inexpensive microcontrollers.

Yikes, that power connector certainly wasn’t designed by Apple. Ugly as it may be, it’s the charging cable for a robot and acts as a sensor that allows the robot to properly align and plug into a power receptacle.

We’re going to go off on a tangent for just a second. We often think of the Rat Things from Snowcrash when considering robot power. They were nuclear powered (or something) and instead of recharging required constant cooling. Those day’s aren’t exactly around the corner but we think they’ve been realized in the lawn mowing robots that have a little nests to recharge in. Base stations work but they require the machine to return to the same place, or to have multiple charging stations.

The point is, this specialized cable makes base stations for robots obsolete. Now a robot can plug into any outlet it can get near, a great thing for robots roving large facilities. After the break you can see a video of this process. The robot arm zeros in by scanning horizontally and vertically and measuring the magnetic field put out by the AC in the wires of the outlet. Take a look, it’s a pretty neat piece of engineering.

[Rockwell] sent us an update on his traffic light hacking. Dedicated readers will remember seeing this legally attained traffic signal controlled through a parallel port from back in 2005. The new update swaps the old port for USB and adds several autonomous functions which are demonstrated in the clip after the break. The update includes a nice UI and some notifications for things like email, IMs, Reddit posts, etc.

He’s given control of the hardware over to an Arduino. Instead of building the board into the project he’s included just the parts he needs; an AVR running the Arduino bootloader, a crystal and filtering caps, and an Arduino serial to USB module for connectivity. The AC load switching is handled by three relays. The relays he links to are 12VCD rated coils. We think this should have pointed to 5VDC coils as that’s the voltage that the logic circuit are running at. Be careful with switching these AC loads, this traffic light isn’t a toy.

[Ryanjmclaughlin] came up with the idea of a Arduino shield that uses TRIACs to switch four channels of AC power. The forum thread he started delves into several interesting discussions covering what it would take to convert this for use with 240v power and of course, a debate about safety.

A reader named [Victor] sent this tip to us and mentioned that this shield might significantly reduce the number of Arduino related projects we see. That’s because mixing high voltage alternating current with delicate 5v logic circuitry can be a bad idea. We’re not saying the creator of this didn’t know what he’s doing, but if you don’t you could fry up your Arduino, or your body.