Repairing and Adding Bluetooth Control to an Induction Cooker

When his 6 years old induction cooker recently broke, [Johannes] decided to open it in an attempt to give it another life. Not only did he succeed, but he also added Bluetooth connectivity to the cooker. The repair part was actually pretty straight forward, as in most cases the IGBTs and rectifiers are the first components to break due to stress imposed on them. Following advice from a Swedish forum, [Johannes] just had to measure the resistance of these components to discover that the broken ones were behaving like open circuits.

He then started to reverse engineer the boards present in the cooker, more particularly the link between the ‘keyboards’ and the main microcontroller (an ATMEGA32L) in charge of commanding the power boards. With a Bus Pirate, [Johannes] had a look at the UART protocol that was used but it seems it was a bit too complex. He then opted for an IOIO and a few transistors to emulate key presses, allowing him to use his phone to control the cooker (via USB or BT). While he was at it, he even added a temperature sensor.

A TTL timer project of yore

[Viktor] just pulled out another one of his decades-old projects. This time around it’s a timer he built using 7400 logic chips. It was a great way for him to learn about electronics, and ended up serving as his alarm clock every morning.

Two pieces of copper clad board were cut to the same size. One of them was etched to act as the circuit board. The other was outfitted as a face plate. The same type of transfer sheets used to mask the traces of the circuit were also used to apply labels to the face plate. It was then coated with acrylic spray to protect it and stave off corrosion. The clock keeps time based on a half-wave rectified signal. The source is from a transformer which steps mains voltage down to a safe level for the 7805 regulator that supplies the clock’s power bus.

We’re glad [Viktor] has been showing off these old projects. We’ve also enjoyed seeing a TV sleep timer he built. If you’ve got something neat for yester-year why not dust it off, post the details, and send us a tip about it?

Wireless iPod charger built from scratch

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.

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Hackaday Links: December 11, 2011

Drilling square holes

We’re still a bit baffled by the physics of this, but apparently it’s possible to drill a square hole with a round bit. This video shows square holes being milled using a cutter which is offset from the center of the bit. [Thanks Jordan]

LED Motorcycle headlight driven by mains

[William] found a way to use a big capacitor and bridge rectifier to run this H4 LED headlight bulb in a mains sconce lamp.

Electronic slide whistle

Here’s an electronic instrument that [Dorian] made. It uses a linear potentiometer and a button and works much like a slide whistle would.

Robot rocks out to Daft Punk

[Adrian] didn’t just make a robot arm out of CD cases and a mints tin. He built the arm, then made a music video featuring it.

More light-pipe sensor experiments

[Uwe] has been working on an input sensor using a flexible light tube. It is a similar idea to these optical flex sensors, but [Uwe] tried several variations like filling the tube with alcohol.

Experimenting with bridge rectifers for AC to DC power conversion

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”

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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Ridiculous exerciser becomes useful as a charger

[Scott Nietfeld] built a charger from a Dyna-flex wrist exerciser. We hadn’t heard of a these gyroscopic devices before but once we saw the promo video (embedded after the break) we realized that this is the kind of thing that infomercials were made to sell. [Scott] knew the internals spun to fairly high RPM and figured that adding a few magnets on the inside and coils on the outside would turn this thing into a generator. Four rare-earth magnets fit the bill, with two external coils feeding a rectifier and linear regulator. Below you can see his demonstration video where he takes the orb apart, then spins it up, generating 250 mA at about 7.5 volts to drive the regulator and charge a cellphone. Not bad!

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