Light Dimmer Shows How to Steal Power from AC Line

We see a lot of traffic on the tips line with projects that cover old ground but do so in an instructive way, giving us insight into the basics of electronics. Sure, commercial versions of this IR-controlled light dimmer have been available for decades. But seeing how one works might just help you design your Next Big Thing.

Like many electronic controls, the previous version of this hack required a connection to a neutral in addition to the hot. This version of the circuit relies on passing a small current through the light bulb the dimmer controls to avoid that extra connection. This design limits application to resistive loads like incandescent bulbs. But it’s still a cool circuit, and [Muris] goes into great detail explaining how it works.

We think the neatest bit is the power supply that actually shorts itself out to turn on the load. A PIC controls a triac connected across the supply by monitoring power line zero-crossing. The PIC controls dimming by delaying the time the triac fires, which trims the peaks off of the AC waveform. The PIC is powered by a large capacitor while the triac is conducting, preventing it from resetting until the circuit can start stealing power again. Pretty clever stuff, and a nice PCB design to boot.

Given the pace of technological and cultural change, it might be that [Muris]’ dimmer is already largely obsolete since it won’t work with CFLs or LEDs. But we can see other applications for non-switched mode transformerless power supplies. And then again, we reported on [Muris]’s original dimmer back in 2009, so the basic design has staying power.

Making a solid-state relay with I2C interface

As [Mic] often got requests to make high-power switching boards, he recently finally gave in and designed the one shown above based around a solid-state relay. Some of our readers that already play with mains power know that switching should normally occur when the voltage crosses zero volts. The ‘TRIAC BLOC’ is able to do so, which also allows mains frequency measurement. [Mic] then tuned to the internal oscillator of his ATtiny microcontroller with this 50Hz by adjusting its OSCCAL register value, so the switching command can be sent at the ideal moment. Zero crossing detection is implemented by feeding the mains into an AC optocoupler. [Mic] discovered that the optocoupler diodes are not identical, so he had to adjust his firmware to account for the time differences.

All the resources are available on github, we would be interested to hear your detailed analysis of the circuit implemented with the passives R3/C1/L1/R8/C3.

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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Dimming LED bulbs designed to replace halogen lamps

dimming-led-halogen-replacementsHalogen bulbs put out a lot of focused light but they do it at the expense of burning up a lot of Watts and generating a lot of heat. The cost for an LED replacement like the one seen disassembled above has come down quite a bit. This drove [Jonathan Foote] to purchase several units and he just couldn’t resist tearing them apart to try out a couple of hacks.

The one we find most interesting is a PWM based dimming hack he pulled off with an Arduino board and a FET. The bulbs are designed to be dimmable through the 12V supply that feeds the light fixture. But the relationship of dimmer position to light level is not linear and [Jonathan] figured he could do better. His solution is to add a FET in parallel with the LEDs. When activated it basically shunts the current around the diodes, resulting in a dimming. The video below shows this in action. We wonder if the flashing is a camera artifact or if you pick that up with your eye as well?

You may also be interested to read his post on Gelling the LED bulbs. Gels are colored filters for lights (or camera lenses). He cuts his preferred color down to size and inserts it between the LEDs and the lenses.

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Months of failure lead up to this EL panel dimmer that pulses to the music


Way back in March [Ch00f] took on a for-hire project to make a suit that lights up to the music. He decided to build something based around a pulsating EL panel. He’s put a lot of time and tried of a few different techniques, but he finally has a working EL panel dimmer.

This is a saga we’ve kept our eye on. The fall seems to have been good to him, after a failure using TRIACS he managed to adjust the brightness of some EL wire by messing with the current going to the driver’s oscillator. Standing on the shoulders of that success he designed the board seen above by getting serious about audio signal processing. There’s a microphone on the board which picks up sound which is then processed into a signal responsible for the brightness of the EL panel.

There’s a demo video after the break, but you’ll want to dig into his article to get all the gritty details.

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Raspberry Pi used to automate a dimmable light bulb


[Stephen] took the safe route when getting his Raspberry Pi to dim an AC light bulb. He didn’t roll his own outlet box with a mains-rated relay inside, going with a mechanical connection instead of electrical. By attaching a servo motor to the dimmer knob the RPi can adjust the light level without risk of electric shock.

He is using the ServoBlaster package to drive the servo motor with the Raspberry Pi GPIO pins. That’s all fine and good by itself, but he went the extra mile and designed a few different levels of functionality around the pairing. The motivation behind the hack was to build a sunrise clock that had a lot of power when it comes to luminosity. But he also plied the RPi’s networking features to serve up a web-based control. It has a slider to set the light level, as well as breath (like a slow fade) and flash features.

The servo is a bit noisy when moving quickly, but the sunrise alarm takes 30 minutes so the gears don’t really make any noise at all. Check it out in the clip after the break.

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Building your own LED-based home lighting

We see LEDs used in all kinds of projects but rarely does someone build a home lighting system from scratch with them. [Paulo Oliveira] decided to give the idea a try, included a fading power supply for the LEDs which he built himself. Here you can see the installation at full brightness, but his controller also offers a single lower setting.

We saw [Sprite_TM] use an RGB LED strip to light up his living room. [Paulo] went with individual LED modules instead, all the same color. They are Cree XM-L power LEDs so some thought needs to be put into heat dissipation. All six are mounted along an aluminum strip which serves as the heat sink. They’re wired in series and powered by an old laptop power supply. A PIC 12F683 uses PWM to dim the string via a MOSFET.

The control system for the two brightness levels uses the wall switch. When turned on, the LEDs fade in to full brightness. If you turn the switch off and back on before they are all the way on, the dimmed setting takes over. This was complicated by the capacitance of the PSU but [Paulo] solved that by adding a power resistor.