Light bulb, diode, and capacitor step mains down to 12V DC

[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.

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Adding Ethernet control for a 5.1 speaker set

[HuB's] set of 5.1 surround sound speakers was gobbling up a bunch of electricity when in standby as evidenced by the 50 Hz hum coming from the sub-woofer and the burning hot heat sink on the power supply. He wanted to add a way to automatically control the systems and offer the new feature of disconnecting the power from the mains.

The first part was not too hard, although he used a roundabout method of prototyping. He planned to use the IR receiver on the speakers to control them. At the time, [HuB] didn’t have an oscilloscope on hand that he could use to capture the IR protocol so he ended up using Audacity (the open source audio editing suite) to capture signals connected to the input of a sound card. He used this to establish the timing and encoding that he needed for all eight buttons on the original remote control.

Next, he grabbed a board that he built using an ATmega168 and an ENC28J60 Ethernet chip. This allows you to send commands via the Internet which are then translated into the appropriate IR signals to control the speakers and a few other devices in the room. The last piece of the puzzle was to wrap an RF controlled outlet into the project with lets him cut mains power to the speakers when not in use. You can see the video demonstration embedded after the break.

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Binary clock using logic chips and mains frequency

[Osgeld] built himself a binary clock. He didn’t take the time to explain his project, but he did post beautifully hand-drawn schematics and pictures of the circuit (PDF) as he was building it. We’ve seen clock projects that use mains frequency as the clock source and that’s the route that [Osgeld] chose for his build. He started with a 9-12V AC wall wort as a power input. From there it’s just a matter of using a bridge rectifier to convert to DC, then a 7805 linear regulator to establish a steady 5V rail. A resistor and a couple of diodes allow him to pull the 60 Hz frequency off of the incoming AC, and then use a combination of 4000 and 7400 logic chips to count the pulses and keep track of the time.