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.

Automated aquarium chemical dispenser is extremely precise


[Robovergne] prides himself on the beautiful reef aquarium that he has set up in his home. These sorts of water displays require constant maintenance due to the mineral requirements of living coral. Rather than add mineral solutions manually, he decided to build a nano-doser using espresso machine pumps (Google Translation).

These vibration pumps run on mains voltage, so he had several options as far as how to control them. Using relays would likely make things pretty noisy, so he chose to use a zero crossing detection circuit to precisely control the pumps’ duty cycles and output.

His setup uses a PIC to control everything from the zero crossing circuit to the display LCD. An amount of product and the distribution time frame are entered using a handful of buttons mounted on the front of his control box, leaving the PIC to do the heavy lifting. It will calculate the proper length of time to run the pump based on several factors, including fluid viscosity and height of release.

It really is an impressive system, and while his needs are very precise, we imagine this sort of setup would be quite useful in building less complicated dispensers, such as those found in an automated bar.

Continue reading to see a few videos of his Nano-doser in action.

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