TRANSFORMER LESS POWER SUPPLY

You can build a robust, small and cheap transformer-less power supply 230 V AC to 5 V DC or 12 V DC practically up to 10 mA using a capacitor resistor zener diodes and normal diodes. The only problem with this kind of power supply is that its not isolated. You will get electric shock if you touch any connections from 5 V side. Refer this document to design yours. Microchip transformer less power supply application note.

TRIAC SWITCH USING A OPTOCOUPLER

The following demo video shows switching ON or OFF a bulb using triac. If you connect this module to a bluetooth module GPIO or a microcontroller GPIO you can control switching of any appliance. Phase switching to control fan speed or bulb intensity is also possible. The circuit uses a optocoupler, triac and few resistors. For circuit diagram refer to this link

REPULSIVE MAGNETIC LEVITATION

Its fascinating to see an object floating in mid air without any direct physical contact. Me, Ruchik, Nagasai and Hemant wanted to build a system that can levitate a Neodymium magnet repulsively in air. One way to do it is using attractive magnetic levitation and other is using repulsive magnetic levitation. Attractive magnetic levitation is easy to achieve but repulsive magnetic levitation is hard to achieve because of the complexity involved in feedback loop. A robust PD feedback control loop is necessary for stable magnetic levitation. In this setup above, the position of the magnet is sensed using hall-effect sensor. This position feedback is used to correct for errors. The hall-effect value is amplified differentiated and applied to the electromagnetic coils to achieve stability. In the setup shown we have used 4 coils, 4 independent PD loops and 4 hall effect sensors. 

ATTRACTIVE MAGNETIC LEVITATION

A principle of operation of a magnetic levitation system is quite simple. If you sense that the magnet is moving down because of gravity pull it up by the attractive force of electromagnet. If you sense that the magnet is moving up because of the force of electromagnet reduce the attractive force of electromagnet so that it moves down. Now you keep doing it continuously so minutely and fast that human eye perceive that the magnet  is floating in mid air. Actually the magnet is moving up and down very fast at very small displacement. If you continue to attract the magnet using the electromagnet it will continue to move up and finally stick to electromagnet. So as soon as you sense that the magnet is moving up you reduce the current in electromagnet so that its attractive force decreases. Now as the magnet starts to drop down you increase the current  in the coil so that its attractive force increases and you pull it back.

REPULSIVE MAGNETIC LEVITATION TRIALS

Trying repulsive magnetic repulsion with Nagasai, Ruchik and Hemant. Looks like magic.