induction – Experimental Engineering

Posted on February 2, 2016 by The Engineer — Leave a comment

Portable Hearing Induction Loop

These units are used to broadcast local audio, such as from a public address system or local microphone. They accomplish this by producing a modulated magnetic field that a hearing aid is capable of picking up.

Not many controls on this bit of equipment. A bi-colour LED for status indications, a microphone, external audio input, charging input & a power switch.

Popping the cover off reveals a small lead-acid battery, 2.1Ah at 12v. This is used when the loop is unplugged.

Here’s the main PCB, which takes care of the audio & battery charging. The inductive loop itself is just visible as the tape-covered wire bundle around the edge of the casing.

Here’s the input section of the main PCB. The microphone input is handled by a SSM2166 front-end preamplifier from Analog Devices.

This audio is then fed into a TDA2003 10W Mono Power Amplifier IC, which directly drives the induction coil as if it were a speaker. Any suitable receiving coil & amplifier can then receive the signal & change it back into audio.

Posted on March 16, 2011March 16, 2011 by The Engineer — Leave a comment

BigBen DSi Inductive Charging Dock

Here is a Inductive charger designed for the Nintendo DSi. Cheap Chinese build, but it does work!

Top has been removed from the unit here. Most prominent in the centre is a solid steel bar, simply there to give the device some weight.
Pair of Tri-colour LEDs at the front indicates charging status.
Induction coil is on the left, with the controller & oscillator PCB at the top.

Closeup of the PCB, ICs have had their markings ground off.

Induction coil. This couples power into a coil built into a special battery, supplied with the base, to charge it when the DSi is placed on the dock.

Information Label on the base.

Standard DSi charger port, connects to the charger you get with the DSi. Power switch is on the right.

Posted on February 14, 2011February 10, 2011 by The Engineer — Leave a comment

Belling Microwave

Here is a cheap no frills microwave oven, which died after a few weeks of normal use.

Cover removed, showing the internals. Front of the microwave is on the left.

Closeup of the timer unit. Cheap & nasty.

Magnetron removed from the oven. Antenna is on the top, cooling fins visible in the center. White conector at the bottom is the filament terminals.

Chokes on the magnetron’s filament connections. These prevent microwave energy from feeding back into the electronics bay through the connections.

Magnetron cooling fins, tube & magnets removed from the frame.

Bare magnetron tube.

This PCB does some rudimentary power conditioning, power resistors are in series with the live feed to the power trasformer, to prevent huge power up surge. When the transformer energizes the relay, which is in parallel with the resistors, switches them out a fraction of a second after, providing full power to the transformer.
Standard RFI choke & capacitor at the top of the board, with the input resistor.

Power transformer to supply the magnetron with high voltage.
Power output is ~2kV at ~0.5A. Pair of spade terminals are the low voltage filament winding.

HV Capacitor. This along with the diode form a voltage doubler, to provide the magnetron with ~4kV DC.

HV diode stack.

Internals of the HV fuse. Rated for ~0.75A at 5kV. The fuse element is barely visible attached to the end of the spring. Connects between the transformer & the capacitor.

Cooling fan for the magnetron. Drive is cheap shaded pole motor.

Fan motor. Basic 240v shaded pole induction type.