Despite the obvious use of a lot of wire, this project is actually a wireless charging system. [Jared] built it as a way to explore the concepts behind transferring power inductively. Alternating current on one of the white coils induces current on the other. This is then rectified, and regulated for use as a 5V charger. In this case it powers his iPod, but any USB device should work with the setup.
The transmitter uses the power supply from an old laptop as a source. Some filtering and a couple of MOSFETS are responsible for generating the AC current on the transmitting coil. The receiving coil feeds the bridge rectifier. In the writeup that voltage is fed to a 7805 regulator to provide a stable 5V output. However, in the video demo after the break [Jared] shows off the boost converter that he uses on his improved circuit. This way if the voltage drops due to poor alignment of the coils it will still be able to provide a steady output.
We’ve seen the same coil concept used to add wireless charging to cellphones too.
Continue reading “Wireless iPod charger built from scratch”
[Karl] needed a programmable real-time clock for one of his projects. He considered adding an RTC chip, LCD screen, and some buttons for use with a microcontroller. That’s not necessarily hard, but it takes time and can be considered a project in itself. Instead, he headed to the hardware store to look for a cheap solution. He was able to get this AC outlet timer for a song. It’s got everything he needs; twenty programmable on/off events, a calendar to track time and day of week, and a user interface made up of a low-power LCD and four buttons. He cracked open the case and patched into the electronics for use with any project.
You can see the solder-tab battery in the middle of the board (green coin-cell). That actually runs the timer circuitry and display. It’s topped off when the unit is plugged into mains, but [Karl] ended up replacing it with a much higher capacity AA rechargeable battery. The device works just like a thermostat, using very little power and driving a relay at the appropriate time. Batteries in thermostats seem to last forever and we can expect the same performance from this device. [Karl] rerouted the trigger signal from the relay to his own 2N2222 transistor. This way the device can switch loads running at voltages other than its own 1.2V operating level.
Stock timers are great. They’re mass-produced which makes them cheap, and you can do some interesting stuff with them. We really enjoyed see this other mechanical version hacked for hydroponic use.
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.
Continue reading “Dimming AC lights the hard way”
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. Continue reading “Experimenting with bridge rectifers for AC to DC power conversion”
[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.
Continue reading “Light bulb, diode, and capacitor step mains down to 12V DC”
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.
[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.