Teoria y

Project: Microcontroller Based Ferromagnetic Material Detector

This design has been divided in to 7 hierarchical blocks, to make it easier to understand. The heart of the design is a DS80C310, a high-speed pin-to-pin compatible replacement for industry standard 8031 microcontroller. This device has enough computation power and address space to satisfy all of the requirements for the project. This example demonstrates how large designs are broken into manageable pieces, some of which can be simulated, while the entire design can be sent to Ultiboard for PCB layout.

The idea behind this project is to use 6kHz resonant tank as a transmitting antenna. Inductor coil L1 (several turns of wire) in parallel to C1 creates a 6kHz resonant tank.

The pump circuit drives the IGB transistor with train of 6 kHz pulses of 25% Duty Cycle. Current inside the tank changes its direction every half period generating an alternate magnetic field around the antenna. Ferromagnetic materials being exposed to this field exhibit a unique behaviour. So-called magnetic domains inside the ferromagnetic materials are forced to line-up with each other and the material magnetizes. By applying a magnetic field of an opposite direction causes the ferromagnetic material to demagnetize and then magnetize with different polarity.

In the process of demagnetization, domains release small amount of energy and create odd harmonics disturbances of electromagnetic field around the antenna. These disturbances are picked up by the receiving antenna and fed into an analog circuitry. Band amplifier circuitry attenuates all unwanted frequencies including 6kHz and amplifies frequencies between 100kHz and 300kHz. Gain is set to about 60dB.

The resulted signal can vary, widely due to the distance between ferromagnetic material and the transmitting/receiving antenna, which requires additional signal conditioning circuitry. The additional circuitry consists of an AGC amplifier, its supporting